AbstractBackgroundAcinetobacter Baumannii Research Articles

2145. Antagonistic Activity of Lacticseibacillus rhamnosus R3 Against Carbapenem-Resistant Acinetobacter baumannii Strain: A Promising Therapeutic Alternative

Abstract Background Acinetobacter baumannii (AB) is a recognized nosocomial pathogen of critical importance Most circulating AB strains are carbapenem-resistant (CRAB), which severely complicates therapeutics with available antibiotics. Probiotic lactic acid bacteria constitute a promising therapeutic alternative. Previously, we determined that Lacticaseibacillus rhamnosus R3 (LR-R3) exerts a strong inhibitory capacity on the model strain A118 (susceptible to antibiotics). In this analysis, the antimicrobial activity of LR-R3 against type CRAB hypervirulent strain AB5075 was evaluated. Figure 1 A) Transwell migration assay. AB5075 viability after 24h exposure to LR-R3 CFCM. B) CFCM activity obtained from 96h culture of LR-R3 on CRAB strains. Methods The inhibitory activity of cell pellet and its cell-free supernatants (CFCM) were determined, respectively, by the soft-agar overlay method, CFCM activity, and transwell migration assay. Also, killing assays and scanning microscopy imaging were performed under co-culture conditions. Lastly, AB5075 transcriptional response when exposed to LR-R3 was assessed by RT-qPCR. Results The lactic acid bacteria LR-R3 demonstrated a strong inhibitory capacity on AB5075 strain (inhibition halo diameter, DHI >20 mm), with loss of cell viability at 4h of co-culture conditions. The CFCM of LR-R3 also showed similar antimicrobial activity on AB5075 (Fig 1A) and against others CRAB strains (Fig 1B), suggesting that the inhibitory effect observed is due to the presence of a compound or metabolite produced and secreted by the lactobacillus. Microscopy images showed increase formation of outer membrane vesicles (OMVs) and the presence of nanotubes. In addition, significant changes in the expression levels of the studied genes were observed in AB5075 in co-culture with LR-R3: increase in the expression of genes involved in biofilm (csuAB, csuB, ompA); and decrease in the expression of genes involved in the synthesis and utilization of iron (bauA, exbD, bfnA, basE, pirA), and genes related to fatty acid and lipid metabolism (paaA, paaB). Conclusion The results obtained allowed the identification of Lcb. rhamnosus R3 as a probiotic strain with antagonistic activity on the nosocomial pathogen A. baumannii. In addition, it was shown that LR-R3 alters iron and fatty acid metabolism, by virtue of this interaction. This work constitutes the basis for future studies necessary to elucidate the mechanism involved. Disclosures Robert A. bonomo, MD, Entasis, Merck, VenatoRx, Wockhardt: Grant/Research Support

500. Impact of an iron chelator on in vitro and in vivo growth of A. baumannii

Abstract Background Acinetobacter baumannii (AB) has become multidrug-resistant in recent years and currently there is no consensus on the optimal treatment for these infections. To combat this urgent threat, novel treatment options are needed to minimize spread and lower mortality rates. Nutrient metals (e.g., iron) are essential to the metabolic functions of AB. If the bioavailability of essential nutrients is restricted, this can cause a bacterial stress response and alter their ability to multiply. Methods The objective of the study was to examine the impact of iron chelation on the growth of AB in vitro and in vivo. MDR AB bloodstream isolates (n=4) were recovered from unique patients between 2011 and 2018. Clonal diversity was ascertained by Fourier Transform Infrared Spectroscopy. In vitro bacterial densities were measured longitudinally over 20-hours to determine the growth profile. Isolates were started at a baseline concentration of approximately 5.5 log CFU/mL in tryptic soy broth. Variable amounts of an iron chelating agent (deferiprone, 0.2-2mM) were added to create a concentration gradient. Galleria mellonella larvae (100-150mg) were inoculated with approximately 5 log CFU of an isolate, with and without deferiprone (10mM). Quantitative culture was used to ascertain the bacterial burden of aggregate larvae (n=10) immediately and 4h post infection. Additional infected larvae (n=20 in each group) were incubated at 35°C and monitored hourly for 24h. Results Time to mortality was compared using Kaplan-Meier survival analysis and log-rank test. Increasing concentrations of the chelating agent caused a transient and concentration-dependent hindrance of in vitro bacterial growth, compared to the no-treatment group. Bacterial burden immediately post-infection of the control and treatment group were comparable at 6.4 log CFU/g. After 4 hours the bacterial burden was much higher in the control group than the treatment group, 8.7 and 6.7 log CFU/g respectively. A trend of delayed mortality was shown in the iron chelator group (median survival 6.5 vs 10 hours, p=0.15). Conclusion These results support that micro-nutrient limitation has the potential to be a novel approach for treating high-risk infections due to MDR AB. Future studies are warranted to further define its optimal place in therapy. Disclosures All Authors: No reported disclosures.

616. Pharmacodynamics (PD) of the lipopeptide QPX9003 Against Acinetobacter baumannii and Pseudomonas aeruginosa in the Neutropenic Mouse Thigh Infection Model

Abstract Background Acinetobacter baumannii and Pseudomonas aeruginosa are important pathogens in hospital-acquired infections and can be resistant to multiple classes of antibiotics. QPX9003 is a novel synthetic lipopeptide that is highly active in vitro against MDR Acinetobacter sp. and P. aeruginosa. The purpose of these studies was to determine the pharmacodynamic parameter that best described the bacterial killing of QPX9003 in vivo. PK-PD of QPX9003 against A. baumannii PK-PD of QPX9003 against P. aeruginosa Methods Seven A. baumannii and six P. aeruginosa isolates were used in these studies. Swiss-Webster mice were rendered neutropenic by 150 mg/kg IP injections of cyclophosphamide 4 and 1 days prior to infection. The bacterial inoculum was prepared from an overnight culture adjusted to 108 CFU/mL then further diluted for inoculation into the thighs. Various dose and dose regimens of QPX9003 were administered by the IP route starting 2 hours post infection and continuing for 24 hours. Untreated control groups were sacrificed at the start of treatment. Treated and untreated control groups were sacrificed 24 hours after the start of treatment, thighs harvested, homogenized and plated to determine colony counts. PK was conducted in neutropenic, infected mice at doses ranging from 3 to 50 mg/kg administered by the IP route. The relationship between PK-PD parameters and the reduction in the log number of CFU per thigh between time zero and 24 h after the start of treatment were analyzed by using the sigmoid maximum reduction (Emax) PD model. Results The activity of QPX9003 was best described by the 24h free AUC/MIC ratio, with stasis and 1 log kill targets of 47.1 and 67.1 for A. baumannii and 96.1 and 117 for P. aeruginosa, respectively. Conclusion The PD of QPX9003 was best described by the 24h free AUC/MIC ratio. Based on the QPX9003 MIC90 for P. aeruginosa (0.25 mg/L) and A. baumannii (1 mg/L), 24h free AUCs between 30 and 67 mg*h/L will produce 1-log of bacterial killing for ∼90% of P. aeruginosa and A. baumannii strains, respectively. QPX9003 is a potentially useful treatment for infections due to P. aeruginosa and A. baumannii, including MDR isolates, that is advancing in clinical studies. Disclosures Ziad Tarazi, Qpex Biopharma: Employee Niki Roos, n/a, Qpex Biopharma: Employee Ted Page, n/a, Qpex Biopharma: Employee David Griffith, n/a, Qpex Biopharma: Employee.

1651. In vitro synergy test and clinical outcome of antibiotics combination regimens for carbapenem-resistant Acinetobacter baumannii

Abstract Background Acinetobacter baumannii is one of the leading etiologic agents of serious hospital-acquired infections. A. baumannii is characterized by a high rate of carbapenem resistance, which often leads to treatment failure and poor outcome. Combination regimens of antibiotics are often used, but their clinical benefit and optimal target are yet unclear. Methods We selected carbapenem-resistant A. baumannii (CRA) isolates from the patients who received antimicrobial treatment for bloodstream infection (2012–2018) or pneumonia (2019–2020) and survived for ≥5 days. In vitro synergy was tested using checkerboard method and time-kill assay for colistin (COL) and tigecycline (TGC) with the following antibiotics: meropenem (MRO), ampicillin/sulbactam (A/S), minocycline (MIN), ciprofloxacin (CIP), and with each other. Clinical information was collected to compare the patient outcome between those who were treated with combination regimens with in vitro synergy and those who were not. Results A total of 72 isolates were selected. When combined with colistin, MRO showed the highest rate of synergy (20.8%), followed by A/S (16.7%), and MIN (13.9%). No antibiotics showed synergy with TGC in >10% of the tested isolates. Most isolates with positive checkerboard test also tested positive with time-kill assay for COL (97.6%), but not for TGC (20.0%). Among 57 patients with monobacterial infection caused by the tested CRA isolates, nine (15.8%) received combination regimens with in vitro synergy. All patients received colistin, and carbapenem was the companion antibiotic in all patients in the synergistic combination group. There was no significant difference in all-cause 30-day mortality (55.6% vs 33.3%, p=0.266), treatment response, and microbiologic response. Multivariable analysis also demonstrated no significant difference in mortality by synergistic combination regimen (adjusted odds ratio, 4.59; 95% confidence interval, 0.73–33.88). Conclusion Checkerboard method showed an excellent concordance with time-kill assay for COL-based combinations, but not with TGC-based regimens. However, combination regimens with a proven in vitro synergy were not associated with better outcomes. Disclosures All Authors: No reported disclosures.

609. In vivo efficacy of human simulated exposures of cefiderocol (FDC) in combination with ceftazidime/avibactam (CZA) or meropenem (MEM) using in a 72 hour murine thigh infection model

Abstract Background Acinetobacter baumannii continues to challenge clinicians as multi-drug resistance limits therapeutic options. CFDC possesses potent in vitro and in vivo activity however combination therapy has been recommended for A. baumannii due to its propensity for multiple resistance mechanisms. The present study utilized clinically relevant exposures of CFDC (2 g IV q8h 3 h infusion) in combination with CZA (2.5 g IV q8h 2 h infusion) or MEM (2 g IV q8h 3h infusion) to evaluate the bactericidal activity and resistance prevention. Methods 15 clinical A. baumannii with the following FDC MICs were assessed: 2 mg/L, n = 3; 8 mg/L, n = 2; ≥ 32 mg/L, n = 10). CZA MICs ranged from 16 - >64 mg/L while MEM MICs ranged from 4 - >64 mg/L. Groups of 6 mice received sham control, CFDC HSR, CFDC + CZA HSR, or CFDC + MEM HSR for 72 h. 1 thigh per mouse was harvested to elucidated bacterial burden at 0 h (baseline) and at 72 h (or when the animal succumbed to infection). Efficacy of the combinations was assessed as change in log10 CFU/thigh relative to CFDC HSR. Development of resistance was defined as > 4 fold increase in MIC relative to that from control animals. Results Untreated controls resulted in robust growth (3.48±0.67). Against isolates with CFDC MICs of 2 mg/L, 2/3 reached 1-log10 kill with CFDC HSR relative to baseline compared with 1/2 and 0/10 isolates with FDC MICs of 8 mg/L and ≥ 32 mg/L, respectively. Against all 15 isolates, CFDC + CZA HSR produced significant kill with a mean -4.77±1.93 reduction in log10 CFU/thigh relative to CFDC treated mice (15/15 ≥1-log10 kill relative to baseline). Similarly, CFDC + MEM HSR produced a mean reduction of -4.13±2.50 relative to CFDC treated mice (12/15 ≥1-log10 kill relative to baseline). Elevated MICs in CFDC treated animals occurred in 3/3 isolates with baseline MICs of 2 mg/L. Of these isolates, 1 developed elevated MICs with CFDC + CZA HSR compared with no isolates with CFDC + MEM HSR. Figure 1. Change in log10 CFU/thigh relative to 0 h control after treatment with cefiderocol HSR, cefiderocol + ceftazidime/avibactam HSR, or cefiderocol + meropenem HSR in the 72 h murine thigh infection model. Cefiderocol MICs are displayed in parentheses. Conclusion The present study using clinical exposures of CFDC, CZA, and MEM suggest the enhanced microbiologic activity of these combinations relative to CFDC alone. Combinations also prevented the development of elevated MICs against 2/3 and 3/3 susceptible isolates with CFDC + CZA and CFDC + MEM, respectively. These data support the clinical evaluation of such combinations against A. baumannii with high CFDC MICs. Disclosures Christian M. Gill, PharmD, Shionogi: Grant/Research Support Miki Takemura, n/a, Shionogi: Employee Christopher M. Longshaw, PhD, Shionogi: Employee Yoshinori Yamano, PhD, Shionogi: Employee Roger Echols, MD, Shionogi: Advisor/Consultant Roger Echols, MD, Shionogi: Advisor/Consultant Roger Echols, MD, Shionogi: Advisor/Consultant David P. Nicolau, PharmD, Shionogi: Grant/Research Support.

655. Combination Eravacycline Therapy for Carbapenem-Resistant Acinetobacter baumannii Pneumonia

Abstract Background Acinetobacter baumannii typically causes infections in debilitated, hospitalized patients and is difficult to treat due to multiple virulence factors and the presence of intrinsic and acquired antibiotic resistance mechanisms leading to frequent isolation of multi-drug resistant (MDR) phenotypes. Due to problematic pharmacokinetics and/or dose-limiting toxicities of salvage agents, combination therapy with aminoglycosides, ampicillin/sulbactam, polymyxins, minocycline, or tigecycline, is often used. Eravacycline has demonstrated greater in-vitro potency against A. baumannii compared to other tetracycline derivatives making it potentially the more appealing option. However, its utility is hindered by a lack of data supporting pharmacodynamic targets and adequate dosing strategies for CRAB. The goal of this case series was to describe our experience with the use of combination eravacycline therapy for the treatment of CRAB pneumonia. Methods This case series included all patients ≥ 18 years of age, diagnosed with SARS-CoV-2, ≥ 1 sputum culture positive for CRAB and a clinical diagnosis of new bacterial pneumonia, who received at least one dose of eravacycline between April 1st and October 1st, 2020. The primary outcome was clinical resolution of CRAB pneumonia. Secondary outcomes evaluated microbiological resolution, need for extended durations of therapy, and frequency of re-starting CRAB therapy within 48 hours of completion. Results In total, 25 patients were included in this case series. The median duration of combination therapy was 10 days. Most patients (96%) received eravacycline + ampicillin/sulbactam, with 7 of those patients also receiving inhaled colistin (Table 2). In total, 17 (68%) patients achieved clinical resolution of CRAB pneumonia. Post-treatment sputum cultures were collected in 18 patients, of which 13 (72%) achieved microbiological resolution. One patient received > 14 days of therapy and no patients re-initiated therapy within 48 hours of eravacycline completion. Table 1:Baseline CharacteristicsTable 2:Study Outcomes Conclusion In this small case series, eravacycline showed favorable clinical outcomes in patients with CRAB pneumonia. In light of limited treatment options, this agent can be considered for CRAB pneumonia salvage therapy. Disclosures All Authors: No reported disclosures.

Increased Capsule Thickness and Hypermotility Are Traits of Carbapenem-Resistant Acinetobacter baumannii ST3 Strains Causing Fulminant Infection.

BackgroundAcinetobacter baumannii is a successful nosocomial pathogen, causing severe, life-threatening infections in hospitalized patients, including pneumonia and bloodstream infections. The spread of carbapenem-resistant Acinetobacter baumannii (CRAB) strains is a major health threat worldwide. The successful spread of CRAB is mostly due to its highly plastic genome. Although some virulence factors associated with CRAB have been uncovered, many mechanisms contributing to its success are not fully understood.MethodsHere we describe strains of CRAB that were isolated from fulminant cases in 2 hospitals in Israel. These isolates show a rare hypermucoid (HM) phenotype and were investigated using phenotypic assays, comparative genomics, and an in vivo Galleria mellonella model. ResultsThe 3 isolates belonged to the ST3 international clonal type and were closely related to each other, as shown by Fourier-transform infrared spectroscopy and phylogenetic analyses. These isolates possessed thickened capsules and a dense filamentous extracellular polysaccharides matrix as shown by transmission electron microscopy (TEM), and overexpressed the capsule polysaccharide synthesis pathway-related wzc gene. ConclusionsThe HM isolates possessed a unique combination of virulence genes involved in iron metabolism, protein secretion, adherence, and membrane glycosylation. HM strains were more virulent than control strains in 2 G. mellonella infection models. In conclusion, our findings demonstrated several virulence factors, all present in 3 CRAB isolates with rare hypermucoid phenotypes.

Molecular typing, biofilm production, and detection of carbapenemase genes in multidrug-resistant Acinetobacter baumannii isolated from different infection sites using ERIC-PCR in Hamadan, west of Iran

BackgroundAcinetobacter baumannii is an opportunistic pathogen that can cause several kinds of nosocomial infections. Increasing antibiotic resistance as well as identifying genetic diversity and factors associated with pathogenicity and prevalence of this bacterium is important. The aim of this study was the investigation of molecular typing, biofilm production, and detection of carbapenemase genes in multidrug-resistant Acinetobacter baumannii isolated from different infection sites using ERIC-PCR in Iran.MethodsForty isolates of A. baumannii were obtained from various wards of the central hospital, in the west of Iran. Phenotypic identification and genetic diversity, biofilm production assay, and detection of Carbapenemase genes carried out.ResultsTracheal samples 26 (61.9 %) are the most frequent isolates, and 95 % of isolates were identified as MDR. 32.5 % of all A. baumannii strains were capable to form a strong biofilm. It was founded that antimicrobial resistance patterns had a significant relationship with strong biofilm formation (P = 0.001). Most frequencies of the studied genes were in the order of VIM (81 %), SPM (45.2 %), and IMP (35.7 %) genes. The VIM gene was the most frequent in all isolates which were significant (P = 0.006). 14 different ERIC-types were observed including 7 common types and 7 unique or single types. F type is the largest common type consisting of nine isolates and B, D, and E types contain two isolates separately.ConclusionsERIC-PCR technique was used to genetically classify A. baumannii isolates as one of the most common microorganisms in nosocomial infections.

Analysis of virulence phenotypes and antibiotic resistance in clinical strains of Acinetobacter baumannii isolated in Nashville, Tennessee

BackgroundAcinetobacter baumannii is a gram-negative bacterium which causes opportunistic infections in immunocompromised hosts. Genome plasticity has given rise to a wide range of strain variation with respect to antimicrobial resistance profiles and expression of virulence factors which lead to altered phenotypes associated with pathogenesis. The purpose of this study was to analyze clinical strains of A. baumannii for phenotypic variation that might correlate with virulence phenotypes, antimicrobial resistance patterns, or strain isolation source. We hypothesized that individual strain virulence phenotypes might be associated with anatomical site of isolation or alterations in susceptibility to antimicrobial interventions.MethodologyA cohort of 17 clinical isolates of A. baumannii isolated from diverse anatomical sites were evaluated to ascertain phenotypic patterns including biofilm formation, hemolysis, motility, and antimicrobial resistance. Antibiotic susceptibility/resistance to ampicillin-sulbactam, amikacin, ceftriaxone, ceftazidime, cefotaxime, ciprofloxacin, cefepime, gentamicin, levofloxacin, meropenem, piperacillin, trimethoprim-sulfamethoxazole, ticarcillin- K clavulanate, tetracyclin, and tobramycin was determined.ResultsAntibiotic resistance was prevalent in many strains including resistance to ampicillin-sulbactam, amikacin, ceftriaxone, ceftazidime, cefotaxime, ciprofloxacin, cefepime, gentamicin, levofloxacin, meropenem, piperacillin, trimethoprim-sulfamethoxazole, ticarcillin- K clavulanate, tetracyclin, and tobramycin. All strains tested induced hemolysis on agar plate detection assays. Wound-isolated strains of A. baumannii exhibited higher motility than strains isolated from blood, urine or Foley catheter, or sputum/bronchial wash. A. baumannii strains isolated from patient blood samples formed significantly more biofilm than isolates from wounds, sputum or bronchial wash samples. An inverse relationship between motility and biofilm formation was observed in the cohort of 17 clinical isolates of A. baumannii tested in this study. Motility was also inversely correlated with induction of hemolysis. An inverse correlation was observed between hemolysis and resistance to ticarcillin-k clavulanate, meropenem, and piperacillin. An inverse correlation was also observed between motility and resistance to ampicillin-sulbactam, ceftriaxone, ceftoxamine, ceftazidime, ciprofloxacin, or levofloxacin.ConclusionsStrain dependent variations in biofilm and motility are associated with anatomical site of isolation. Biofilm and hemolysis production both have an inverse association with motility in the cohort of strains utilized in this study, and motility and hemolysis were inversely correlated with resistance to numerous antibiotics.

813. The Reduction of the acquisition rate of carbapenem resistant Acinetobacter baumannii after room privatization in the intensive care unit

Background Acinetobacter baumannii is one of the major pathogens of hospital-acquired infection recently and hospital outbreaks have been reported worldwide. On September 2017, New intensive care unit(ICU) with only single rooms, remodeling from old ICU with multibed bay rooms, was opened in an acute-care tertiary hospital in Seoul, Korea. We investigated the effect of room privatization in the ICU on the acquisition of carbapenem-resistant Acinetobacter baumannii(CRAB).MethodsWe retrospectively reviewed medical records of patients who admitted to the medical ICU in a tertiary care university-affiliated 1,800-bed hospital from 1 January 2015 to 1 January 2019. Patients admitted to the medical ICU before the remodeling of the ICU were designated as the control group, and those who admitted to the medical ICU after the remodeling were designated as the intervention group. Then we compared the acquisition rate of CRAB between the control and intervention groups. Patients colonized with CRAB or patients with CRAB identified in screening tests were excluded from the study population. The multivariable Cox regression model was performed using variables with p-values of less than 0.1 in the univariate analysis.ResultsA total of 1,105 cases admitted to the ICU during the study period were analyzed. CRAB was isolated from 110 cases in the control group(n=687), and 16 cases in the intervention group(n=418). In univariate analysis, room privatization, prior exposure to antibiotics (carbapenem, vancomycin, fluoroquinolone), mechanical ventilation, central venous catheter, tracheostomy, the presence of feeding tube(Levin tube or percutaneous gastrostomy) and the length of ICU stay were significant risk factors for the acquisition of CRAB (p< 0.05). In the multivariable Cox regression model, the presence of feeding tube(Hazard ratio(HR) 4.815, 95% Confidence interval(CI) 1.94-11.96, p=0.001) and room privatization(HR 0.024, 95% CI 0.127-0.396, p=0.000) were independent risk factors.Table 1. Univariate analysis of Carbapenem-resistant Acinetobacter baumannii Table 2. Multivariable Cox regression model of the acquisition of Carbapenem-resistant Acinetobacter baumannii ConclusionIn the present study, room privatization of the ICU was correlated with the reduction of CRAB acquisition independently. Remodeling of the ICU to the single room would be an efficient strategy for preventing the spreading of multidrug-resistant organisms and hospital-acquired infection.Disclosures All Authors: No reported disclosures

1610. Epidemiology and Treatment Heterogeneity in Acinetobacter baumanii Infections

Background Acinetobacter baumannii is known as a highly resistant organism causing serious infections in intensive care populations. However, the epidemiology of infections caused by Acinetobacter baumannii and approaches to treatment are not well described in a national healthcare system.MethodsOur retrospective cohort study included patients with positive Acinetobacter baumannii cultures collected from any source during hospitalizations at Veterans Affairs (VA) medical centers nationally from January 2010 to April 2019. We evaluated patient characteristics and utilized exposure mapping to identify treatment patterns, including treatment heterogeneity. Heterogeneity was defined as patterns of antibiotic treatment (drug and duration) not shared by any other patient.ResultsOur study included 7,551 admissions with positive Acinetobacter baumannii cultures. The mean age was 66.7 years (±12.1) and 97.4% were male. Most patients were admitted from other healthcare facilities (59.2%) and 20.8% were in intensive care during the admission. Most patients had their culture collected on the day after admission and the median time to culture completion was 4 days (interquartile range 3-5). Acinetobacter baumannii cultures were most commonly obtained from urine (33.6%), followed by skin and soft tissue (25.3%), lung (21.8%), blood (9.2%), and bone/joint (5.0%). The median length of hospital stay was 11 days, with inpatient mortality and 30-day mortality rates of 11.6% and 12.5%, respectively.Treatment heterogeneity was high, with 88.5% of admissions having different antibiotic treatment patterns (drug and duration), with a median time to first change of 1 day and median of 3 changes. Only 2% of the admissions were treated with polymyxins and 3.0% with colistin. Carbapenems were used in 18.9% of the admissions and extended-spectrum cephalosporins in 31.7% of the admissions.ConclusionIn VA hospitals, Acinetobacter baumannii infections are observed in both critical and non-critical patient populations, mostly among patients with healthcare exposures. Acinetobacter baumannii infections were found to have various sources of infection, mostly from urine and skin and soft tissue, and approaches to treatment were highly varied.Disclosures Aisling Caffrey, PhD, Merck (Research Grant or Support)Pfizer (Research Grant or Support)Shionogi (Research Grant or Support) Haley J. Appaneal, PharmD, Shionogi, Inc. (Research Grant or Support) Kerry LaPlante, PharmD, Merck (Advisor or Review Panel member, Research Grant or Support)Ocean Spray Cranberries, Inc. (Research Grant or Support)Pfizer Pharmaceuticals (Research Grant or Support)Shionogi, Inc. (Research Grant or Support)

Characterization of carbapenem-resistant hypervirulent Acinetobacter baumannii strains isolated from hospitalized patients in the mid-south region of China

BackgroundAcinetobacter baumannii has traditionally been considered an opportunistic pathogen with low virulence. In this study, we characterized the carbapenem-resistant hypervirulent A. baumannii (CR-hvAB) stains isolated from our hospital in mid-south region of China.ResultsBlood samples collected between January 2017 and May 2019 were used for virulence experiments and biofilm assays of individual carbapenem-resistant A. baumannii (CR-AB) strains, performed using a Galleria mellonella infection model and crystal violet staining method, respectively. CR-AB isolates that induced high mortality in the G. mellonella infection model were subjected to genotyping, susceptibility testing, and clinical data analysis, and the genetic characterization of these isolates was performed by whole-genome sequencing (WGS). Among the 109 CR-AB clinical strains, the survival rate of G. mellonella larvae infected with 7 (6.4%) CR-AB isolates (number of strains with mortality of 0, 10 and 20% was 4, 1, and 2, respectively), was significantly lower than that of A. baumannii ATCC 19606 (100.0%) and the remaining CR-AB isolates (> 80.0%). Consistent with these results, patients infected with these seven isolates had an average 7-day mortality rate of 42.9%, suggesting that the isolates were CR-hvAB. These seven isolates belonged to four sequence types (STs): ST457, ST195, ST369, and ST2088 (a new ST), and mainly ST457 (n = 4). The results of the biofilm study showed that eight strains had powerful biofilm ability (strong [n = 1] and moderate [n = 7] biofilm producers) including these seven CR-hvAB isolates.ConclusionsCR-hvAB isolates that induced a high mortality rate were cloned in our hospital, most of which belonged to ST457; thus, monitoring of these strains, particularly ST457, should be strengthened in the future. Meanwhile, A. baumannii, which was isolated from blood specimens and found to powerful biofilm-forming ability, is a probable hvAB isolate.

Integrative analysis of outer membrane vesicles proteomics and whole-cell transcriptome analysis of eravacycline induced Acinetobacter baumannii strains

BackgroundAcinetobacter baumannii is a multidrug-resistant (MDR) hazardous bacterium with very high antimicrobial resistance profiles. Outer membrane vesicles (OMVs) help directly and/or indirectly towards antibiotic resistance in these organisms. The present study aims to look on the proteomic profile of OMV as well as on the bacterial transcriptome upon exposure and induction with eravacycline, a new synthetic fluorocycline. RNA sequencing analysis of whole-cell and LC-MS/MS proteomic profiling of OMV proteome abundance were done to identify the differential expression among the eravacycline-induced A. baumannii ATCC 19606 and A. baumannii clinical strain JU0126.ResultsThe differentially expressed genes from the RNA sequencing were analysed using R package and bioinformatics software and tools. Genes encoding drug efflux and membrane transport were upregulated among the DEGs from both ATCC 19606 and JU0126 strains. As evident with the induction of eravacycline resistance, ribosomal proteins were upregulated in both the strains in the transcriptome profiles and also resistance pumps, such as MFS, RND, MATE and ABC transporters. High expression of stress and survival proteins were predominant in the OMVs proteome with ribosomal proteins, chaperons, OMPs OmpA, Omp38 upregulated in ATCC 19606 strain and ribosomal proteins, toluene tolerance protein, siderophore receptor and peptidases in the JU0126 strain. The induction of resistance to eravacycline was supported by the presence of upregulation of ribosomal proteins, resistance-conferring factors and stress proteins in both the strains of A. baumannii ATCC 19606 and JU0126, with the whole-cell gene transcriptome towards both resistance and stress genes while the OMVs proteome enriched more with survival proteins.ConclusionThe induction of resistance to eravacycline in the strains were evident with the increased expression of ribosomal and transcription related genes/proteins. Apart from this resistance-conferring efflux pumps, outer membrane proteins and stress-related proteins were also an essential part of the upregulated DEGs. However, the expression profiles of OMVs proteome in the study was independent with respect to the whole-cell RNA expression profiles with low to no correlation. This indicates the possible role of OMVs to be more of back-up additional protection to the existing bacterial cell defence during the antibacterial stress.

Rapid and accurate detection of carbapenem-resistance gene by isothermal amplification in Acinetobacter baumannii.

Background Acinetobacter baumannii (A. baumannii) is one of the pivotal pathogens responsible for nosocomial infections, especially in patients with low immune response, and infection with carbapenem-resistant A. baumannii has been increasing in recent years. Rapid and accurate detection of carbapenem-resistance genes in A. baumannii could be of immense help to clinical staff.MethodsIn this study, a 15-μL reaction system for recombinase polymerase amplification (RPA) was developed and tested. We collected 30 clinical isolates of A. baumannii from the Burn Institute of Southwest Hospital of Third Military Medical University (Army Medical University) for 6 months and tested antibiotic susceptibility using the VITEK 2 system. A. baumannii was detected based on the blaOXA-51 gene by PCR, qPCR and 15 μL-RPA, respectively. Sensitivity and specificity were evaluated. In addition, PCR and 15 μL-RPA data for detecting the carbapenem-resistance gene blaOXA-23 were comparatively assessed.ResultsThe detection limit of the blaOXA-51 gene by 15 μL RPA was 2.86 CFU/ml, with sensitivity comparable to PCR and qPCR. No positive amplification signals were detected in non-Acinetobacter isolates, indicating high specificity. However, only 18 minutes were needed for the 15 μL RPA assay. Furthermore, an antibiotic susceptibility test showed that up to 90% of A. baumannii strains were resistant to meropenem and imipenem; 15 μL RPA data for detecting blaOXA-23 showed that only 10% (n = 3) of A. baumannii isolates did not show positive amplification signals, and the other 90% of (n = 27) isolates were positive, corroborating PCR results.ConclusionWe demonstrated that the new 15 μL RPA assay for detecting blaOXA-23 in A. baumannii is faster and simpler than qPCR and PCR. It is a promising alternative molecular diagnostic tool for rapid and effective detection of A. baumannii and drug-resistance genes in the field and point-of-care testing.

The sensor kinase BfmS controls production of outer membrane vesicles in Acinetobacter baumannii

BackgroundAcinetobacter baumannii is an important opportunistic pathogen responsible for various nosocomial infections. The BfmRS two-component system plays a role in pathogenesis and antimicrobial resistance of A. baumannii via regulation of bacterial envelope structures. This study investigated the role of the sensor kinase, BfmS, in localization of outer membrane protein A (OmpA) in the outer membrane and production of outer membrane vesicles (OMVs) using wild-type A. baumannii ATCC 17978, ΔbfmS mutant, and bfmS-complemented strains.ResultsThe ΔbfmS mutant showed hypermucoid phenotype in the culture plates, growth retardation under static culture conditions, and reduced susceptibility to aztreonam and colistin compared to the wild-type strain. The ΔbfmS mutant produced less OmpA in the outer membrane but released more OmpA via OMVs than the wild-type strain, even though expression of ompA and its protein production were not different between the two strains. The ΔbfmS mutant produced 2.35 times more OMV particles and 4.46 times more OMV proteins than the wild-type stain. The ΔbfmS mutant OMVs were more cytotoxic towards A549 cells than wild-type strain OMVs.ConclusionsThe present study demonstrates that BfmS controls production of OMVs in A. baumannii. Moreover, BfmS negatively regulates antimicrobial resistance of A. baumannii and OMV-mediated host cell cytotoxicity. Our results indicate that BfmS negatively controls the pathogenic traits of A. baumannii via cell envelope structures and OMV production.

A multimodal intervention program to control a long-term Acinetobacter baumannii endemic in a tertiary care hospital

BackgroundAcinetobacter baumannii causes frequently nosocomial infections worldwide. Its ability to survive on dry surfaces facilitates its spread and the persistence of endemic situations, especially in the intensive care units (ICUs).The objective of this paper is to describe a multicomponent intervention program designed to control a hyperendemic persistence of multidrug-resistant A. baumannii (MDR-Ab) and to characterize its impact.MethodsDesign: Quasi-experimental intervention study based on open cohorts.Setting: Public tertiary referral centre. Period: January 2009–August 2017.Intervention: multifaceted program based on environmental decontamination, hand hygiene, antimicrobial stewardship, contact precautions, active surveillance, weekly reports and regular meetings.Analysis: joinpoint regression and interrupted time-series analysis.ResultsThe intervention was successfully implemented. Through the study period, the compliance with contact precautions changed from 0 to 100% and with hand hygiene, from 41.8 to 82.3%. Between 2012 and 2016, the antibiotic consumption decreased from 165.35 in to 150.44 daily-defined doses/1000 patients-days in the ICU. The incidence density of MDR-Ab in the ICU was 10.9 cases/1000 patients-days at the beginning of the intervention. After this moment, the evolution of the incidence density of MDR-Ab was: between months 0 and 6°, it remained stable; between months 7° and 10°: there was an intense decrease, with an average monthly percentage change (AMPC) = − 30.05%; from 11° month until the end, the decrease was lighter but continuous (AMPC:-2.77%), achieving an incidence density of 0 cases/1000 patients-days on the 18° month, without any new case for 12 months. From the 30° month until the end of the study period, several little outbreaks of MDR-Ab were detected, all of them rapidly controlled. The strains of MDR-Ab isolated during these outbreaks were not clonally related with the previously endemic one, which supports its eradication from the environmental reservoirs.ConclusionThe multicomponent intervention performed by a multidisciplinary team was effective to eradicate the endemic MDR-Ab.

581. The Epidemiology of Imipenem-Resistant Acinetobacter baumannii Bacteremia in a Pediatric Intensive Care Unit and Carbapenem Use

Background Acinetobacter baumannii (AB) infections cause high mortality and morbidity in intensive care unit patients. There are limited data on the epidemiology of imipenem-resistant A. baumannii (IRAB) amongst pediatric ICU patients.MethodsA retrospective chart review was performed in patients with AB bacteremia in a pediatric intensive care unit at a tertiary teaching hospital from January 2000 to December 2016. Antimicrobial susceptibility tests, multilocus sequence typing (MLST) and PCR for antimicrobial resistance genes were performed for stored isolates. In addition, antibiotic prescription days of therapy (DOT per 1,000 patient-days) of the pediatric department from January 2001 to December 2016 was analyzed.ResultsBacteremia episodes occurred in 27 patients. Male patients were 11 (41%) and the median age at the onset of bacteremia was 5.2 years (range, 0–18.6 years). There was a clear shift in antibiogram of AB during the study period. From 2000 to 2003, all isolates were imipenem-sensitive (ISAB, N = 6). From 2005 to 2008, both IRAB (N = 5) and ISAB (N = 4) were isolated. However, since 2009, all the AB isolates were IRAB (N = 12). In 33% (9/27) of patients, first AB was isolated from tracheal aspirate and patients developed bacteremia later (median duration from AB positive tracheal culture to AB positive blood culture, 8 days [range 5–124]). The overall mortality of patients with AB bacteremia was 59.3% (16/27) within 28 days. There was no statistical difference in mortality between ISAB and IRAB groups (50% vs. 71%; P = 0.42). From MLST analysis of 10 available isolates, sequence type 138 was predominant (N = 7). All 10 isolates were positive for OXA-23-like and OXA-51-like carbapenemase. In 2001, carbapenem DOT per 1,000 patient-days was 15.3 and later strikingly raised to 82.5 in 2009 when all the isolates were imipenem resistant. After this IRAB outbreak in PICU, proactive infection control and antimicrobial stewardship were reinforced among multidisciplinary teams in PICU. IRAB outbreak was terminated and carbapenem DOT per 1,000 patient-days was decreased to 51.7 in 2016.ConclusionIRAB bacteremia causes serious threat in high-risk pediatric patients in PICU. Proactive infection control measures and antimicrobial stewardship are crucial to manage serious IRAB infection in PICU.Disclosures All authors: No reported disclosures.

1219. Disinfection of Surfaces Contaminated with Carbapenemase Producing Acinetobacter baumannii Using Ozone Under Complex Room Conditions

Background Acinetobacter baumannii is an emerging multiresistant Gram-negative rod, which has caused multiple hospital outbreaks. A. baumannii can display a high ability to survive on inanimate surfaces. Therefore, cleaning and disinfection is an important part in the prevention of A. baumannii transmission. No-touch room decontamination is performed with increasing frequency to reach more standardization in hospital cleaning. In this study, we investigated the efficacy of an automated room decontamination using ozone (Sterisafe™ pro) against A. baumannii under complex room conditions.MethodsA Carbapenemase-producing A. baumannii outbreak strain was analyzed with respect to its ability to survive on dry surfaces. The Sterisafe™ pro instrument was used in a patient room with an attached bathroom. The A. baumannii strain was dried on three different carriers (ceramic tiles, stainless steel, solid core furniture board) and placed at eight different positions in the rooms. A standard disinfection cycle (80 ppm ozone; 90 % RH; 60 minutes) was conducted in three independent experiments.ResultsThe A. baumannii strain displayed a long-term survival on surfaces under dry conditions sufficient for further disinfection experiments. Interestingly, the mean reduction rates of A. baumannii dried on three surfaces displayed significant differences. Reduction rates greater than 5 log were reached on all stainless steel and ceramic carriers even under the complex room conditions using the standard disinfection cycle of the Sterisafe™ pro instrument. In contrast, on furniture board individual carriers displayed reduction rates of even less than 4 log. The mean reduction rate was still 5 log for A. baumannii on furniture board.Conclusion A. baumannii dried on different surfaces display a differential susceptibility against automated ozone disinfection. However, the SterisafeTM pro instrument displayed a sufficient reduction of A. baumannii for all tested surfaces even under complex room conditions. The individual behavior of A. baumannii on different materials indicate the necessity for the validation of automated room decontamination systems under varying conditions.Disclosures All authors: No reported disclosures.

1542. The Evaluation of the In Vitro Synergy of Colistin in Combination with Meropenem and Tigecycline against 50 Multi-Drug-resistant Acinetobacter baumannii strains

Background Acinetobacter baumannii possess inherent and acquired antibiotic resistance mechanisms that have rendered most antibiotics, including carbapenems, inactive. Colistin (COL) has risen as salvage therapy against these organisms due to its retained activity against A. baumannii. However, COL monotherapy is often met with suboptimal outcomes. Recently, combination therapy with COL and meropenem (MEM) or tigecycline (TGC) has been shown to be effective in eradicating multi-drug-resistant A. baumannii infections. The objective of this study was to further evaluate the efficacy of COL in combination with MEM or TGC against 50 multi-drug-resistant A. baumannii strains.MethodsFifty carbapenem-resistant A. baumannii strains were evaluated using combination minimum inhibitory concentration (MIC) testing and time-kill analysis (TKA). Single-drug MIC testing was performed for each strain by broth microdilution. Combination MIC testing was performed for COL+MEM and COL+TGC. Each strain was evaluated via 24-hour TKA to assess the synergistic capabilities of COL+MEM, and COL+TGC. Synergy was defined as a ≥ 2-log reduction CFU/mL in either combination from the most active single agent, while bactericidal activity was defined as a ≥ 3-log reduction CFU/mL of either combination from the initial inoculum.ResultsAll 50 strains were resistant to MEM and TGC with MICs ≥ 64 µg/mL and ≥ 4 µg/mL respectively; while 3 strains were resistant to COL, MICs ≥ 2 µg/mL. MEM and TGC MIC values were reduced as much as 128-fold (median 2-fold) and 32-fold (median 2-fold),, respectively, in the presence of subinhibitory COL. COL MIC values were reduced as much as 512-fold (median 4-fold) from baseline in the presence of subinhibitory MEM, and as high as 16-fold (median 2-fold) in the presence of TGC. In TKAs, COL+MEM was synergistic in 45/50 (90%) strains and bactericidal against 43/50 (86%) strains. COL+TGC TKAs revealed synergy in 32/50 (64%) strains, and bactericidal activity against 28/50 (56%) strains.ConclusionThe combinations of COL+MEM and COL+TGC demonstrate promise in combating highly resistant A. baumannii. Further research is mandated to explore other combinations that are capable of eradicating multi-drug-resistant A. baumannii.Disclosures All authors: No reported disclosures.

Investigation of multidrug-resistant ST2 Acinetobacter baumannii isolated from Saint George hospital in Lebanon

BackgroundAcinetobacter baumannii is an opportunistic pathogen causing various nosocomial infections. The spread of multidrug-resistant A. baumannii is a major public health problem. The aim of this study was to investigate the molecular epidemiology and the genetic support of multidrug-resistant A. baumannii isolates collected from Saint-Georges Hospital in Lebanon.MethodsBetween January and August 2016, 31 A. baumannii isolates were collected from sputum samples of patients infected with ventilator-associated pneumonia (VAP) and treated with colistin-carbapenem combination therapy. Antibiotic susceptibility testing was performed using the disk diffusion method. Carbapenemases, extended spectrum β-lactamases encoding genes and mcr-1/2 genes were investigated by RT-PCR and standard PCR. The epidemiological relatedness of the strains was studied using MLST analysis.ResultsMost of the isolates exhibited multidrug-resistant phenotypes. All the isolates were carbapenem-resistant and among them, 30 carried the class D carbapenemase blaoxa-23 gene while one isolate carried blaoxa-72 gene. MLST results revealed three sequence types, namely ST2, ST699, and ST627. Isolates having ST2 were the most prevalent clone (29/31, 93.5%).ConclusionsThis study shows a nosocomial spread of multidrug-resistant A. baumannii ST2 having blaOXA-23 gene in Saint-George in Lebanon. Monitoring and control measures need to be adopted to avoid the spread of A. baumannii to patients.