Drug-resistant Acinetobacter Baumannii Research Articles

Analysis of Efflux Pump System and Other Drug Resistance Related Gene Mutations in Tigecycline-Resistant Acinetobacter baumannii.

The isolation of tigecycline-resistant Acinetobacter baumannii in recent years has brought great difficulties to clinical prevention and treatment. To explore the effect of efflux pump system and other resistance related gene mutations on tigecycline resistance in Acinetobacter baumannii. Fluorescence quantitative PCR was used to detect the expression levels of major efflux pump genes (adeB, adeJ, and adeG) in extensive drug-resistant Acinetobacter baumannii. The minimum inhibitory concentration (MIC) of tigecycline was detected by the broth microdilution testing and efflux pump inhibition experiment to assess the role of efflux pump in tigecycline resistance of Acinetobacter baumannii. Efflux pump regulatory genes (adeR and adeS) and tigecycline resistance related genes (rpsJ, trm, and plsC) were amplified by PCR and sequenced. By sequence alignment, tigecycline sensitive and tigecycline-insensitive Acinetobacter baumannii were compared with standard strains to analyze the presence of mutations in these genes. The relative expression of adeB in the tigecycline-insensitive Acinetobacter baumannii was significantly higher than that in the tigecycline sensitive Acinetobacter baumannii (114.70 (89.53-157.43) vs 86.12 (27.23-129.34), P = 0.025). When efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP) was added, the percentage of tigecycline-insensitive Acinetobacter baumannii with tigecycline MIC decreased was significantly higher than that of tigecycline-sensitive Acinetobacter baumannii (10/13 (76.9%) vs 26/59 (44.1%)), P = 0.032); the relative expression of adeB in the MIC decreased group was significantly higher than that in the MIC unchanged group (110.29 (63.62-147.15) vs 50.06 (26.10-122.59), P = 0.02); The relative expression levels of efflux pumps adeG and adeJ did not increase significantly, and there was no significant difference between these groups. One adeR point mutation (Gly232Ala) and eight adeS point mutations (Ala97Thr, Leu105Phe, Leu172Pro, Arg195Gln, Gln203Leu, Tyr303Phe, Lys315Asn, Gly319Ser) were newly detected. Consistent mutations in trm and plsC genes were detected in both tigecycline-insensitive and tigecycline-sensitive Acinetobacter baumannii, but no mutation in rpsJ gene was detected in them. Tigecycline-insensitive Acinetobacter baumannii efflux pump adeABC overexpression was an important mechanism for tigecycline resistance, and the mutations of efflux pump regulator genes (adeR and adeS) are responsible for adeABC overexpression. The effect of trm, plsC, and rpsJ gene mutations on the development of tigecycline resistance in Acinetobacter baumannii remains controversial.

Assessment of the synergistic effect of seven antimicrobial combinations on extensively drug-resistant Acinetobacter baumannii strains

Background: To solve the difficulty in determining the appropriate treatment regimen for patients infected with extensively drug-resistant Acinetobacter baumannii (XDRAB), it is necessary to develop various strategies to increase the therapeutic effect of antimicrobial agents. The purpose of this study was to select the treatment combination showing the greatest antimicrobial effect among seven candidate antimicrobial substances. Methods: Seven strains of XDRAB were used in this study. The composition of the treatment consisted of colistin as the base and one of the seven antimicrobial substances, doripenem, minocycline, tigecycline, linezolid, fusidic acid, vancomycin, or alyteserin E4K peptide. The interaction between the drugs in each combination was evaluated by measuring the synergy rates using time-kill analysis. Results: The synergy rates of the seven combinations tested in the time-kill assay in this study were as follows, in descending order from the combination with the highest synergy rate: colistin + minocycline (57.1%), colistin + alyteserin E4K (50.0%), colistin + tigecycline (42.9%), colistin + vancomycin (28.6%), colistin + doripenem (14.3%), colistin + fusidic acid (14.3%), and colistin + linzolid (0%). None of the combinations showed antagonism. The three combinations showing bactericidal activity and the rates of their bactericidal activity were colistin + alyteserin E4K combination (33.3%), colistin + minocycline (14.3%), and colistin + vancomycin (14.3%). Conclusion: The colistin + minocycline and colistin + alyteserin E4K treatment combinations, which showed high synergy rates, can be considered as promising candidates for future in vivo experiments evaluating combination therapies.

1192. Containment of Sustained Transmission of Drug-resistant Acinetobacter baumannii by Pulsed-Xenon Ultraviolet Disinfection of the Patient Room in the Intensive Care Unit

Abstract Background No-touch environmental disinfection has been highlighted in the last decade to control transmission of multidrug-resistant Gram-positive organisms including MRSA and VRE, but its effectiveness to control gram-negative bacteria has not been well examined. Also, its effectiveness outside the US healthcare setting is seldom reported. Methods This study was conducted in the intensive care unit (ICU) of Yamagata University Hospital, a 637-bed tertiary referral hospital. Sporadic acquisition of two drug-resistant Acinetobacter baumannii (2DRA) began in late 2013. Despite various infection control practices including hand hygiene promotion and intensified manual terminal cleaning, transmission of this pathogen continued. In February 2018, pulsed-xenon ultraviolet (PX-UV) disinfection was added. The study periods were defined as follows: the baseline period (August 2016 to January 2018, intensified manual cleaning) and the intervention period (February 2018 to December 2021, addition of PX-UV). Throughout the study periods, all patients were regularly screened for 2DRA to detect acquisition of those pathogens in the ICU. Results The incidence of newly acquired 2DRA significantly declined over time (4.45 per 1,000 patient days in the baseline period to 1.20 in the intervention period, relative risk (RR): 0.27, 95% confidence interval: 0.12-0.61). Notably, horizontal transmission of 2DRA was completely contained, not only in the ICU but also throughout the hospital (Figure). Newly acquired 2DRA events (all wards, monthly) Conclusion Adding PX-UV after through manual terminal cleaning is effective in controlling acquisition of 2DRA in the ICU patients and led to termination of transmission of 2DRA in our hospital. The effectiveness of PX-UV in controlling gram-negative MDROs in the non-US healthcare settings is suggested. Disclosures All Authors: No reported disclosures.

Triple combination of SPR741, clarithromycin, and erythromycin against Acinetobacter baumannii and its tolerant phenotype.

Extensively drug-resistant (XDR) Acinetobacter baumannii poses a severe threat to public health due to its ability to form biofilms and persister cells, which contributes to critical drug resistance and refractory device-associated infections. A novel strategy to alleviate such an emergency is to identify promising compounds that restore the antimicrobial susceptibility of existing antibiotics against refractory infections. Here, we found a significant synergy among three combinations of SPR741, clarithromycin and erythromycin with a potent antimicrobial activity against XDR A. baumannii (SPR741/CLA/E at 8/10/10 μg ml-1 for XDR AB1069 and at 10/16/10 μg ml-1 for XDR AB1208, respectively). Moreover, the triple combination therapy exhibits a significant antipersister and antibiofilm effect against XDR strains. Mechanistic studies demonstrate that SPR741 may promote intracellular accumulation of macrolides by permeabilizing the outer membrane as well as disrupting membrane potential and further enhance the quorum sensing inhibition activity of the macrolides against XDR A. baumannii and its biofilms. In addition, the triple combination of SPR741 with clarithromycin and erythromycin was not easy to induce resistance in A. baumannii and had effective antimicrobial activity with low toxicity in vivo. Collectively, these results reveal the potential of SPR741 in combination with clarithromycin and erythromycin as a clinical therapy for refractory infections caused by XDR A. baumannii.

Repurposed dihydroorotate dehydrogenase inhibitors with efficacy against drug-resistant Acinetobacter baumannii

New antimicrobials are needed for the treatment of extensively drug-resistant Acinetobacter baumannii. The de novo pyrimidine biosynthetic enzyme dihydroorotate dehydrogenase (DHODH) is a validated drug target for malaria and human autoimmune diseases. We provide genetic evidence that A.baumannii DHODH (AbDHODH) is essential for bacterial survival in rodent infection models. We chemically validate the target by repurposing a unique library of ~450 triazolopyrimidine/imidazopyrimidine analogs developed for our malaria DHODH program to identify 21 compounds with submicromolar activity on AbDHODH. The most potent (DSM186, DHODH IC50 28 nM) had a minimal inhibitory concentration of ≤1 µg/ml against geographically diverse A.baumannii strains, including meropenem-resistant isolates. A structurally related analog (DSM161) with a long in vivo half-life conferred significant protection in the neutropenic mouse thigh infection model. Encouragingly, the development of resistance to these compounds was not identified in vitro or in vivo. Lastly, the X-ray structure of AbDHODH bound to DSM186 was solved to 1.4 Å resolution. These data support the potential of AbDHODH as a drug target for the development of antimicrobials for the treatment of A.baumannii and potentially other high-risk bacterial infections.

Colistin Monotherapy versus Combination Therapy for Carbapenem-Resistant Organisms

BackgroundPneumonia and bloodstream infections (BSI) due to extensively drug-resistant (XDR) Acinetobacter baumannii, XDR Pseudomonas aeruginosa, and carbapenem-resistant Enterobacterales (CRE) are associated with high mortality rates, and therapeutic options remain limited. This trial assessed whether combination therapy with colistin and meropenem was superior to colistin monotherapy for the treatment of these infections.MethodsThe OVERCOME (Colistin Monotherapy versus Combination Therapy) trial was an international, randomized, double-blind, placebo-controlled trial. We randomly assigned participants to receive colistin (5 mg/kg once followed by 1.67 mg/kg every 8 hours) in combination with either meropenem (1000 mg every 8 hours) or matching placebo for the treatment of pneumonia and/or BSI caused by XDR A. baumannii, XDR P. aeruginosa, or CRE. The primary outcome was 28-day mortality, and secondary outcomes included clinical failure and microbiologic cure.ResultsBetween 2012 and 2020, a total of 464 participants were randomly assigned to treatment, and 423 eligible patients comprised the modified intention-to-treat population. A. baumannii was the predominant trial pathogen (78%) and pneumonia the most common index infection (70%). Most patients were in the intensive care unit at the time of enrollment (69%). There was no difference in mortality (43 vs. 37%; P=0.17), clinical failure (65 vs. 58%; difference, 6.8 percentage points; 95% confidence interval [CI], −3.1 to 16.6), microbiologic cure (65 vs. 60%; difference, 4.8 percentage points; 95% CI, −5.6 to 15.2), or adverse events (acute kidney injury, 52 vs. 49% [P=0.55]; hypersensitivity reaction, 1 vs. 3% [P=0.22]; and neurotoxicity, 5 vs. 2% [P=0.29]) between patients receiving monotherapy and combination therapy, respectively.ConclusionsCombination therapy with colistin and meropenem was not superior to colistin monotherapy for the treatment of pneumonia or BSI caused by these pathogens. (Funded by the National Institute of Allergy and Infectious Diseases, Division of Microbiology and Infectious Diseases protocol 10-0065; ClinicalTrials.gov number, NCT01597973.)

Synergetic dual antibiotics-loaded chitosan/poly (vinyl alcohol) nanofibers with sustained antibacterial delivery for treatment of XDR bacteria-infected wounds

Resistance of bacterial pathogens to conventional antibiotics has remained a significant challenge in managing post-wound infections, especially in developing countries. Here, a nanofibrous chitosan/poly (vinyl alcohol) (CS/PVA) mat was designed for controlled delivery of three different concentrations of two antibiotics (colistin/meropenem ratio of 32/64 μg/ml (AB1), 64/128 μg/ml (AB2), and 128/256 (AB3) μg/ml) with synergistic antibacterial activity against ATCC and extensively drug-resistant (XDR) Acinetobacter baumannii clinical isolates. The scaffolds showed a uniform fibrous structure with no bead formation with a sustained release of the antibiotics for one week. The elongation at break, wettability, porosity, and average fiber diameter decreased with increased antibiotics concentrations. Young's modulus and tensile strength showed a significant increase after adding antibiotics. All the constructs showed excellent in vitro cytocompatibility for fibroblasts and biocompatibility in an animal model. The antibacterial assays confirmed the dose-dependent antibacterial activity of the CS/PVA. The scaffolds loaded with AB2 and AB3 showed biocidal properties against ATCC, while only CS/PVA/AB3 had antibacterial activity against XDR clinical isolates. This study suggests the CS/PVA/AB3 nanofibrous scaffold contained 128/256 μg/ml colistin/meropenem as an excellent antibacterial wound dressing for protection of skin wounds from XDR clinical isolates and now promises to proceed with pre-clinical investigations.

Growth kinetics of multiple Acinetobacter baumannii resistotype after meropenem-based antibiotic combination exposure.

Background: Carbapenems are the treatment of choice for multidrug-resistant (MDR) and extensively drug-resistant (XDR) Acinetobacter baumannii infections, but the emergence of carbapenem-resistant A. baumannii (CRAB) has rendered it ineffective in the vast majority of cases. Combination therapy has grown in popularity over the last decade; this study aims to analyze A.baumannii growth kinetics after exposure to meropenem and ampicillin-sulbactam compared with meropenem and amikacin antibiotic combinations in clinically relevant concentrations. Methods: This experimental laboratory study was conducted on the A. baumannii ATCC 19606 isolate and three clinical isolates that were intermediate or resistant to tested antibiotics. Meropenem and ampicillin-sulbactam, as well as meropenem and amikacin, were tested at four different concentrations against isolates. Turbidity measurements were taken at predetermined time points of 0, 1, 2, 4, 6, 8, and 24 hours following exposure; bacterial concentration was enumerated using the agar plate method, with the results plotted in a time-kill curve. Results: A bactericidal effect was achieved in isolates that were intermediate to ampicillin-sulbactam and resistant to meropenem after the administration of meropenem and ampicillin-sulbactam combination with a concentration of 4 µg/ml and 16/8 µg/ml, respectively. The combination of meropenem and ampicillin-sulbactam demonstrated bacteriostatic activity against isolates that were resistant to both antibiotics. Isolates treated with resistant antibiotics showed an increased growth rate compared to the growth control. Conclusion: The combination of meropenem and ampicillin-sulbactam could be a promising combination therapy in treating CRAB infections. The mechanism and degree of antibiotic resistance in the isolates affect the efficacy of antibiotic combinations; further research is needed to corroborate the findings of this study.

Comment on Huang et al. Colistin Monotherapy versus Colistin plus Meropenem Combination Therapy for the Treatment of Multidrug-Resistant Acinetobacter baumannii Infection: A Meta-Analysis. J. Clin. Med. 2022, 11, 3239

In the recently published meta-analysis titled "Colistin Monotherapy versus Colistin plus Meropenem Combination Therapy for the Treatment of Multidrug-Resistant Acinetobacter baumannii Infection: A Meta-Analysis", Huang et al. compared the efficacy and safety of treatment with colistin monotherapy versus colistin plus meropenem combination therapy in patients with drug-resistant Acinetobacter baumannii infection [...].

Alkaline tea tree oil nanoemulsion nebulizers for the treatment of pneumonia induced by drug-resistant Acinetobacter baumannii

The infectious pneumonia induced by drug-resistant Acinetobacter baumannii (DRAB), a hospital-acquired bacterial infection, has a high morbidity and mortality rate. A natural essential oil, tea tree oil (TTO), has a high bactericidal effect without the potential of drug resistance; however, its volatility, hydrophobicity and poor stability limit its applications. Here, TTO nanoemulsions (nanoTTOs) were prepared with the spontaneous-emulsification method. The size of nanoTTOs was 293.2 nm, and the zeta potential was −15.0 mV. They became nebulizers when they were transformed to fine aerosols with a vibrating screen nebulizer. The aerosols had a mass median aerodynamic diameter size of 2.53 μm and a fine particle fraction (1–5 μm) of 86.65%, suitable for pulmonary delivery. The minimum bactericidal concentration (MBC) of nanoTTOs against DRAB was 10.40 mg/mL; while the alkaline nanoTTOs doped with 1.0% NaHCO3 had the MBC of 6.50 mg/mL. Pulmonary delivery of the alkaline nanoTTOs showed obvious therapeutic effects on the DRAB pneumonic mice by downregulating the pro-inflammatory cytokines (IL-1β and IL-6), preventing the bacterial proliferation, and reducing the lung injury, better than ordinary nanoTTOs. Alkaline nanoTTOs are a promising nebulizer formulation for the treatment of bacterial pneumonia, especially drug-resistant bacterial pneumonia.

Molecular Characterization and Antibiogram of Acinetobacter baumannii Clinical Isolates Recovered from the Patients with Ventilator-Associated Pneumonia.

A 2-year prospective study carried out on ventilator-associated pneumonia (VAP) patients in the intensive care unit at a tertiary care hospital, Hail, Kingdom of Saudi Arabia (KSA), revealed a high prevalence of extremely drug-resistant (XDR) Acinetobacter baumannii. About a 9% increase in the incidence rate of A. baumannii occurred in the VAP patients between 2019 and 2020 (21.4% to 30.7%). In 2019, the isolates were positive for IMP-1 and VIM-2 (31.1% and 25.7%, respectively) as detected by PCR. In comparison, a higher proportion of isolates produced NDM-1 in 2020. Here, we observed a high proportion of resistant ICU isolates towards the most common antibiotics in use. Colistin sensitivity dropped to 91.4% in the year 2020 as compared to 2019 (100%). Thus, the finding of this study has a highly significant clinical implementation in the clinical management strategies for VAP patients. Furthermore, strict implementation of antibiotic stewardship policies, regular surveillance programs for antimicrobial resistance monitoring, and screening for genes encoding drug resistance phenotypes have become imperative.

Preferential Selection of Low-Frequency, Lipopolysaccharide-Modified, Colistin-Resistant Mutants with a Combination of Antimicrobials in Acinetobacter baumannii.

ABSTRACTColistin, which targets lipopolysaccharide (LPS), is used as a last-resort drug against severe infections caused by drug-resistant Acinetobacter baumannii. However, A. baumannii possesses two colistin-resistance mechanisms. LPS modification caused by mutations in pmrAB genes is often observed in clinical isolates of multidrug-resistant Gram-negative pathogens. In addition to LPS modification, A. baumannii has a unique colistin resistance mechanism, a complete loss of LPS due to mutations in the lpxACD genes, which are involved in LPS biosynthesis. This study aimed to elucidate the detailed mechanism of the emergence of colistin-resistant A. baumannii using strains with the same genetic background. Various colistin-resistant strains were generated experimentally using colistin alone and in combination with other antimicrobials, such as meropenem and ciprofloxacin, and the mutation spectrum was analyzed. In vitro selection of A. baumannii in the presence of colistin led to the emergence of strains harboring mutations in lpxACD genes, resulting in LPS-deficient colistin-resistant strains. However, combination of colistin with other antimicrobials led to the selection of pmrAB mutant strains, resulting in strains with modified LPS (LPS-modified strains). Further, the LPS-deficient strains showed decreased fitness and increased susceptibility to many antibiotics and disinfectants. As LPS-deficient strains have a higher biological cost than LPS-modified strains, our findings suggested that pmrAB mutants are more likely to be isolated in clinical settings. We provide novel insights into the mechanisms of resistance to colistin and provide substantial solutions along with precautions for facilitating current research and treatment of colistin-resistant A. baumannii infections.IMPORTANCE Acinetobacter baumannii has developed resistance to various antimicrobial drugs, and its drug-resistant strains cause nosocomial infections. Controlling these infections has become a global clinical challenge. Carbapenem antibiotics are the frontline treatment drugs for infectious diseases caused by A. baumannii. For patients with infections caused by carbapenem-resistant A. baumannii, colistin-based therapy is often the only treatment option. However, A. baumannii readily acquires resistance to colistin. Many patients infected with colistin-resistant A. baumannii undergo colistin treatment before isolation of the colistin-resistant strain, and it is hypothesized that colistin resistance predominantly emerges under selective pressure during colistin therapy. Although the concomitant use of colistin and carbapenems has been reported to have a synergistic effect in vitro against carbapenem-resistant A. baumannii strains, our observations strongly suggest the need for attention to the emergence of strains with a modified lipopolysaccharide during treatment.

Evaluating the Efficacy of Eravacycline and Omadacycline against Extensively Drug-Resistant Acinetobacter baumannii Patient Isolates

For decades, the spread of multidrug-resistant (MDR) Acinetobacter baumannii has been rampant in critically ill, hospitalized patients. Traditional antibiotic therapies against this pathogen have been failing, leading to rising concerns over management options for patients. Two new antibiotics, eravacycline and omadacycline, were introduced to the market and have shown promising results in the treatment of Gram-negative infections. Since these drugs are newly available, there is limited in vitro data about their effectiveness against MDR A. baumannii or even susceptible strains. Here, we examined the effectiveness of 22 standard-of-care antibiotics, eravacycline, and omadacycline against susceptible and extensively drug-resistant (XDR) A. baumannii patient isolates from Cooper University Hospital. Furthermore, we examined selected combinations of eravacycline or omadacycline with other antibiotics against an XDR strain. We demonstrated that this collection of strains is largely resistant to monotherapies of carbapenems, fluoroquinolones, folate pathway antagonists, cephalosporins, and most tetracyclines. While clinical breakpoint data are not available for eravacycline or omadacycline, based on minimum inhibitory concentrations, eravacycline was highly effective against these strains. The aminoglycoside amikacin alone and in combination with eravacycline or omadacycline yielded the most promising results. Our comprehensive characterization offers direction in the treatment of this deadly infection in hospitalized patients.

Extensively drug-resistant Acinetobacter baumannii co-producing VIM-2 and OXA-23 in intensive care units: Results of a one-day point prevalence in a Tunisian hospital

ObjectiveThe main objective of this study was to identify carbapenem resistance mechanisms among clinical, commensal and environmental carbapenem-resistant Acinetobacter baumannii (CRAB) strains isolated in 5 Tunisian intensive care units (ICUs). Materials and MethodsCRAB isolates were recovered from different sources: clinical specimens, rectal and environmental swabs. Bacterial identification was carried out using conventional methods and susceptibility testing according to EUCAST recommendations. Evaluation of phenotypic carbapenemase production of was performed using seven different methods, and molecular detection of carbapenemase-coding genes (blaOXA23, blaOXA24, blaOXA58, blaNDM, blaGES, blaOXA48, blaIMP, blaVIM and blaKPC) was done by PCR. The genetic relationships between CRAB isolates were analyzed by pulsed-field gel electrophoresis. ResultsAll in all, 46 CRAB isolates were identified in clinical specimens (n = 26/26), rectal swabs (n = 17/36) and environmental swabs (n = 3/63). Most of them (n = 41/46) were clonally related and found in the different ICUs. All of the CARB isolates harbored blaOXA-51-like and blaOXA-23 genes, while blaVIM-2 gene was detected in 42 isolates (91.3 %). Phenotypic carbapenemase activity was found in all 46 strains, using the CIM-Tris test with 100 % sensitivity for OXA-23 and VIM-carbapenemase detection, thereby justifying its routine use. ConclusionThe emergence and diffusion of clonal CRAB strains inducing high mortality rates in ICUs is a major public health concern. Enhanced infection control practices and mandatory staff education are needed to control the spread of these multidrug-resistant bacteria.

In Vitro and In Vivo Antimicrobial Activity of the Novel Peptide OMN6 against Multidrug-Resistant Acinetobacter baumannii.

The rapid worldwide spread of antimicrobial resistance highlights the significant need for the development of innovative treatments to fight multidrug-resistant bacteria. This study describes the potent antimicrobial activity of the novel peptide OMN6 against a wide array of drug-resistant Acinetobacter baumannii clinical isolates. OMN6 prevented the growth of all tested isolates, regardless of any pre-existing resistance mechanisms. Moreover, in vitro serial-passaging studies demonstrated that no resistance developed against OMN6. Importantly, OMN6 was highly efficacious in treating animal models of lung and blood infections caused by multidrug-resistant A. baumannii. Taken together, these results point to OMN6 as a novel antimicrobial agent with the potential to treat life-threatening infections caused by multidrug-resistant A. baumannii avoiding resistance.

Draft genome sequences of extensively drug resistant and pandrug resistant Acinetobacter baumannii strains isolated from hospital wastewater in South Africa

Acinetobacter baumannii is a significant opportunistic pathogen causing nosocomial infections. Infections caused by A. baumannii are often difficult to treat because this bacterium is often multidrug-resistant and shows high environmental adaptability. Here, we report on the analysis of three A. baumannii strains isolated from hospital effluents in South Africa. Strains were isolated on Leeds Acinetobacter agar and were identified using VITEK®2 platform. Antibiotic susceptibility testing was performed using the Kirby-Bauer Disk diffusion method. Whole-genome sequencing was performed. The assembled contigs were annotated. Multilocus sequence type, antimicrobial resistance, and virulence genes were identified. The strains showed two multilocus sequence types, ST231 (FA34) and ST1552 (PL448, FG116). Based on their antibiotic susceptibility profiles, PL448 and FG116 were classified as extensively drug-resistant and FA34 as pandrug-resistant. FA34 harbored mutations in LpxA, LpxC, and PmrB, conferring resistance to colistin, but not mcr genes. All three strains encoded virulence genes for immune evasion (capsule, lipopolysaccharide [LPS]), iron uptake, and biofilm formation. FA34 was related to human strains from South Africa; PL448 and FG116 were related to a strain isolated in the United States from a human wound. The detection of extensively drug- and pandrug-resistant A. baumannii strains in hospital effluents is of particular concern. It indicates that wastewater might play a role in the spread of these bacteria. Our data provide insight into the molecular epidemiology, resistance, pathogenicity, and distribution of A. baumannii in South Africa.

A Randomized Controlled Trial of Colistin Combined with Sulbactam: 9 g per Day versus 12 g per Day in the Treatment of Extensively Drug-Resistant Acinetobacter baumannii Pneumonia: An Interim Analysis.

Extensively drug-resistant A. baumannii (XDRAB) pneumonia has a high mortality rate in hospitalized patients. One of the recommended treatments is colistin combined with sulbactam; however, the optimal dosage of sulbactam is unclear. In an open-label, superiority, randomized controlled trial, patients diagnosed with XDRAB pneumonia were randomly assigned (1:1) to receive colistin in combination with sulbactam at either 9 g/day or 12 g/day. The primary outcome was the 28-day mortality rate in the intention-to-treat population. A total of 88 patients received colistin in combination with sulbactam at a dosage of either 12 g/day (n = 45) or 9 g/day (n = 43). Trends toward a lower mortality rate were observed in the 12 g/day group at 7 days (11.1% vs. 23.3%), 14 days (33.3% vs. 41.9%), and 28 days (46.7% vs. 58.1%). The microbiological cure rate at day 7 was significantly higher in the 12 g/day group (90.5% vs. 58.1%; p = 0.02). Factors associated with mortality at 28 days were asthma, cirrhosis, APACHEII score ≥ 28, and a dosage of sulbactam of 9 g/day for mortality at any timepoint. Treatment with colistin combined with sulbactam at 12 g/day was not superior to the combination treatment with sulbactam at 9 g/day. However, due to being an interim analysis, this trial was underpowered to detect mortality differences.

Tn7382, a novel composite transposon harboring blaNDM-1 and aphA6 in Acinetobacter baumannii

ObjectivesCo-transfer of carbapenem and amikacin resistance might contribute to the evolution of extensively drug resistant (XDR) Acinetobacter baumannii. The current study used bioinformatic tools and an in silico approach to investigate the potential mobility of a novel composite transposon co-harboring blaNDM-1 and aphA6. MethodsThe transposon, named here Tn7382, was recently identified in the chromosomes of two XDR A. baumannii isolates (M02 and M11) from Egypt. The draft genomes of M02 and M11 were generated by Illumina sequencing. Nucleotide homology of Tn7382 and flanking regions was analyzed using the Basic Local Alignment Search Tool. ResultsTn7382 is derived from Tn125 and encompasses seven open reading frames [aphA6, ISAba125 transposase-coding gene, blaNDM-1, ble, iso, tat, cutA] enclosed by two direct copies of ISAba14. While described for the first time, Tn7382 was found in the chromosomes of five A. baumannii strains deposited in the NCBI database. Using the Artemis Comparison Tool, the potential mobility of Tn7382 was demonstrated in silico by comparative genomic analysis of two A. baumannii strains (TP1 and TP2) retrieved from the NCBI database. The transposon was acquired by TP2 at the same location as an ISAba14 element in the ancestral variant TP1 isolated from the same patient in the USA 11 days earlier. ConclusionsHere, we present the characteristics of Tn7382, a composite transposon flanked by ISAba14 and harboring the aphA6 and blaNDM-1 resistance genes. In silico analysis inferred the potential mobility of Tn7382, but experimental validation is still required.

Enhancing thermal stability and lytic activity of phage lysin PlyAB1 from Acinetobacter baumannii.

With the increasingly serious drug resistance of Acinetobacter baumannii, there is an increasingly urgent need for new antibacterial drugs. Phage lysin PlyAB1 has a bactericidal effect on drug-resistant A. baumannii, which has the potential to replace antibiotics to fight infection caused by A. baumannii. However, its application is limited by its thermal stability and lytic activity. To solve these problems, molecular dynamics (MD) simulations combined with Hotspot wizard 3.0 were used to identify key residue sites affecting thermal stability, and evolutionary analysis combined with multiple sequence alignment was used to identify key residue sites affecting lytic activity. Four single-point variants with significantly increased thermal stability and four single-point variants with significantly lytic activity were obtained, respectively. Furthermore, by superimposing mutations, we obtained three double-point variants, G100Q/K69R, G100R/K69R, and G100K/K69R, with significantly improved thermal stability and improved lytic activity. At 45°C,the lytic activity and half-life of the optimal variant G100Q/K69R were 1.51-and 24-foldhigher than those of the wild PlyAB1, respectively. These results deepen our understanding of the structure and function of phage lysin and contribute to the application of phage lysin in antibiotic substitution.

An outbreak investigation of extensively drug-resistant Acinetobacter baumannii cases in the intensive care unit of Al-Qatif Central Hospital, Saudi Arabia

Background: Acinetobacter baumannii has emerged as an extremely disturbing pathogen for several institutions worldwide. It is common in hospital environments, and outbreaks of Acinetobacter infections classically arise in intensive care units (ICUs). This investigation aimed to describe the extensively drug-resistant Acinetobacter baumannii (XDRAB) outbreak, which occurred in the intensive care unit (ICU) of Al-Qatif central hospital, Saudi Arabia. Methodology: This is a cross-sectional study for all positive (XDRAB) reported cases in the ICU of Al-Qatif Central Hospital, Eastern region during August and September 2019. Investigation of cases was based on the patient’s files, charts, lab records, interviewing the infection prevention and control team of the hospital, and the directorate. Microbiological and environmental samples were collected and tested for XDRAB. Results: A total of nine patients tested positive. Eight of the cases were male, and only three of them were Non-Saudi. The age ranged from 21 to 82 years, the mean age was 48.6 ± 21.14 years, and the mean length of ICU stay was eight ± 5.75 days. The environmental samples and the swabs from the health care workers (HCW) hand results were negative for XDRAB. Eight of the nine affected patients were on a mechanical ventilator (OR 9.2, 95% CI:1.09-77.9, P = 0.029), and according to the control chart, there was a previous outbreak attack in early 2019. Conclusion: The ICU of Al-Qatif hospital experienced an XDRAB outbreak in August, and it continued till September 2019. There was a previous outbreak with the same organism early in the same year, which required a strong adherence to the control and prevention measures and further analytical studies to find out the reasons behind the recurrent XDRAB outbreak. Key Words: Acinetobacter baumannii, outbreak investigation, drug-resistance, Saudi Arabia.