Cefepime Resistance Research Articles

Effect of X-ray radiation on Multi-drug Resistant (MDR) Enterobacteriaceae & P.aeruginosa isolated from burn unit patient. The phenotypic and molecular study, Biofilm formation

Background: Multi-drug-resistant (MDR) bacteria are a significant global health concern due to their elevated rates of morbidity and mortality in burn patients. In This study investigated the presence of multidrug-resistant pathogenic bacteria in individuals with burn injuries, the formation of biofilms, and the impact of X-ray radiation. Method: For this study Clinical swabs about120 burn patients were obtained between December 2023 and June 2024 from burn units at Ramadi and Falluja Teaching Hospitals. Both conventional and Vitek2(bioMérieux) methods were used to identify the bacterial isolates. The isolates were then divided into three multi-drug resistance groups. The Colorimetric method (MTP) detected biofilms. To detect blaOXA-23,blaOXA-48, Omp, and blaTEM resistance genes, multiplex PCR was used. This research used two lumbosacral spine X-ray levels. Two levels of radiation were used 40 (80KV) mAs and 51.2 (85KV). Result: Results of burn isolation revealed 30(27%) P.aeruginosa, 18(16%) k.pneumoniae, 7(6%) E.coli, 7(6%) P.mirabilis. Of the all isolates, 100% produced biofilm. The Multiplex-PCR analysis revealed that the blaTEM genes were the predominant ones, constituting 30% of the samples. Subsequently, blaOXA-23 constituted 24.5% of the cases, whereas Omp accounted for 22.7% and blaOXA-48 for 13.6%. The radiation impact of X-rays produced by two dosages, 40(80KV)mAs for 125msec and 51,2(85KV) mAs for 160msec, demonstrates that there is no effect or alteration in the resistance capacity of all the bacterial isolates tested. Conclusion: This study showed that burn unit isolates produce ESBLs, which is a major concern in the intensive care unit due to its high morbidity and potential mortality. These data match antibiotic phenotypic test results showing substantial cefepime resistance. All isolates forming biofilms, this may association with high pathogenicity. This demands quick intervention to manage nosocomial outbreaks. No X-ray effect was seen on susceptibility a burn unit bacterial isolate.

Toward an optimization of empirical antibiotic therapy in acute graft pyelonephritis: A retrospective multicenter study

ObjectiveAcute graft pyelonephritis (AGPN) is the most frequent infectious complication in kidney transplant recipients (KTR). The treatment of acute community-acquired (CA) pyelonephritis is based on third-generation cephalosporins (3GC) and fluoroquinolones. Cefepime or a piperacillin-tazobactam combination are more often used in healthcare-associated (HCA) infections. However, these recommendations do not consider the resistance observed in KTRs. The objective of our study was to define the most appropriate empirical antibiotherapy for AGPN in KTRs according to the CA and HCA settings. To answer this question, we assessed the prevalence of resistance to different antibiotics usually recommended for urinary tract infections (UTIs) in the general population. MethodsObservational, retrospective, multicenter study covering all episodes of AGPN occurring in hospitalized KTRs in 2019. ResultsA total of 210 patients were included in 7 centers and 244 episodes of AGPN were analyzed (158 CA-AGPN and 86 HCA-AGPN). The prevalence of 3GC and fluoroquinolone resistance was 23 % (n = 36) and 30 % (n = 50) in CA infections (n = 158), and 47 % (n = 40) and 31 % (n = 27) in HCA infections (n = 86), respectively. Cefepime resistance rate was 19 % (n = 30) in CA-AGPN and 29 % (n = 25) in HCA-AGPN. Piperacillin-tazobactam combination had resistance rates > 15 % in both CA and HCA infections. The only antimicrobials with resistance rates < 10 % were aminoglycosides and carbapenems. ConclusionNone of the antibiotics recommended in empirical treatment in UTIs has shown a resistance rate of less than 10% with regard to AGPN. Therefore, none of them should be used as monotherapy. A combination therapy including amikacin could be an appropriate strategy in this setting.

Detection of resistance integrons among biofilm and non-biofilm producing clinical isolates of Pseudomonas aeruginosa.

Integrons are genetic systems that may confer antibiotic resistance to Pseudomonas aeruginosa. Biofilm formation can facilitate gene exchange and can accelerate the development of antibiotic resistance. The aim of this work was to assess the distribution of resistance integrons including class 1, 2 and 3 among biofilm- and non-biofilm producing clinical strains of P. aeruginosa. We also aimed to investigate the relationship between the existence of these integrons and the isolates' resistance patterns. Specimens were obtained from patients showing evidence of infection. P. aeruginosa isolates were identified using conventional techniques, while disk diffusion test was used to detect their antimicrobial susceptibilities. Biofilm formation was detected by the tissue culture plate technique, while classes of integrons were detected by polymerase chain reaction. Out of 106 P. aeruginosa isolates, 55.7% were class 1 integron-positive while 19.8% were class 2 integron-positive. However, class 3 integrons were not detected. Significant associations were found between class 1 integrons and resistance toward amikacin, gentamicin, cefepime, ceftazidime and ciprofloxacin. Class 2 integrons were associated with amikacin, ceftazidime and cefepime resistance. Of pseudomonal isolates, 61.3% were biofilm producing. Biofilm production was associated significantly with the existence of class 1 integrons (p<0.001) and class 2 integrons (p=0.039). About two thirds of isolated strains harbored resistance integrons, which emphasized their significance in our locality. The frequencies of class 1 and 2 integrons were significantly higher among biofilm forming isolates. Ongoing surveillance and infection control strategies are necessary to limit spread of integrons.

Focusing on Gordonia Infections: Distribution, Antimicrobial Susceptibilities and Phylogeny.

The immunosuppression conditions and the presence of medical devices in patients favor the Gordonia infections. However, the features of this aerobic actinomycete have been little explored. Strains (n = 164) were characterized with 16S rDNA and secA1 genes to define their phylogenetic relationships, and subjected to broth microdilution to profile the antimicrobial susceptibilities of Gordonia species that caused infections in Spain during the 2005-2021 period. Four out of the eleven identified species were responsible for 86.0% of the infections: Gordonia sputi (53.0%), Gordonia bronchialis (18.3%), Gordonia terrae (8.5%) and Gordonia otitidis (6.1%). Respiratory tract infections (61.6%) and bacteremia (21.9%) were the most common infections. The secA1 gene resolved the inconclusive identification, and two major clonal lineages were observed for G. sputi and G. bronchialis. Species showed a wide antimicrobial susceptibility profile. Cefoxitin resistance varies depending on the species, reaching 94.2% for G. sputi and 36.0% for G. terrae. What is noteworthy is the minocycline resistance in G. sputi (11.5%), the clarithromycin resistance in G. bronchialis secA1 lineage II (30.0%) and the amoxicillin-clavulanate and cefepime resistance in G. terrae (21.4% and 42.8%, respectively). G. sputi and G. bronchialis stand out as the prevalent species causing infections in Spain. Resistance against cefoxitin and other antimicrobials should be considered.

Prevalence and Antibiogram Pattern of Klebsiella pneumoniae in a Tertiary Care Hospital in Makkah, Saudi Arabia: An 11-Year Experience.

Infectious disease is one of the greatest causes of morbidity and mortality worldwide, and with the emergence of antimicrobial resistance, the situation is worsening. In order to prevent this crisis, antimicrobial resistance needs to be monitored carefully to control the spread of multidrug-resistant bacteria. Therefore, in this study, we aimed to determine the prevalence of infection caused by Klebsiella pneumoniae and investigate the antimicrobial profile pattern of K. pneumoniae in the last eleven years. This retrospective study was conducted in a tertiary hospital in Makkah, Saudi Arabia. Data were collected from January 2011 to December 2021. From 2011 to 2021, a total of 61,027 bacterial isolates were collected from clinical samples, among which 14.7% (n = 9014) were K. pneumoniae. The antibiotic susceptibility pattern of K. pneumoniae revealed a significant increase in the resistance rate in most tested antibiotics during the study period. A marked jump in the resistance rate was seen in amoxicillin/clavulanate and piperacillin/tazobactam, from 33.6% and 13.6% in 2011 to 71.4% and 84.9% in 2021, respectively. Ceftazidime, cefotaxime, and cefepime resistance rates increased from 29.9%, 26.2%, and 53.9%, respectively, in 2011 to become 84.9%, 85.1%, and 85.8% in 2021. Moreover, a significant increase in the resistance rate was seen in both imipenem and amikacin, with an average resistance rate rise from 6.6% for imipenem and 11.9% for amikacin in 2011 to 59.9% and 62.2% in 2021, respectively. The present study showed that the prevalence and drug resistance of K. pneumoniae increased over the study period. Thus, preventing hospital-acquired infection and the reasonable use of antibiotics must be implemented to control and reduce antimicrobial resistance.

Low-Level Cefepime Exposure Induces High-Level Resistance in Environmental Bacteria: Molecular Mechanism and Evolutionary Dynamics.

Antibiotics exert selective pressures on clinically relevant antibiotic resistance. It is critical to understand how antibiotic resistance evolves in environmental microbes exposed to subinhibitory concentrations of antibiotics and whether evolutionary dynamics and emergence of resistance are predictable. In this study, Comamonas testosteroni isolated from wastewater activated sludge were subcultured in a medium containing 10 ng/mL cefepime for 40 days (∼300 generations). Stepwise mutations were accumulated, leading to an ultimate 200-fold increase in the minimum inhibitory concentration (MIC) of cefepime. Early stage mutation in DNA polymerase-encoding gene dnaE2 played an important role in antibiotic resistance evolution. Diverse resistance mechanisms were employed and validated experimentally, including increased efflux, biofilm formation, reduced antibiotic uptake, and drug inactivation. The cefepime minimal selective concentrations (MSCs) and relative fitness of susceptible, intermediate, and resistant mutants were determined. Agent-based modeling of the modified Moran process enabled simulations of resistance evolution and predictions of the emergence time and frequency of resistant mutants. The unraveled cefepime resistance mechanisms could be employed by broader bacteria, and the newly developed model is applicable to the predictions of general resistance evolution. The improved knowledge facilitates the assessment, prediction, and mitigation of antibiotic resistance progression in antibiotic-polluted environments.

228. Epidemiology and Susceptibility Profiles of ST131-O25b Escherichia coli Detected Among Cephalosporin and/or Carbapenem-Resistant Isolates Collected in United States Hospitals

228. Epidemiology and Susceptibility Profiles of ST131-O25b <i>Escherichia coli</i> Detected Among Cephalosporin and/or Carbapenem-Resistant Isolates Collected in United States Hospitals

408. Impact of the COVID-19 Pandemic on Antimicrobial Use and Resistance in the United States and the Dominican Republic

Abstract Background The disease caused by SARS-CoV-2, COVID-19, has caused a global public health crisis. Lower respiratory tract infections (LRTIs) caused by COVID-19 has led to an increase in hospitalizations. Disease severity and concerns for bacterial co-infections can increase antimicrobial pressure. Our aim is to define and compare the impact of COVID-19 on antimicrobial use (AU) and antimicrobial resistance (AMR) in the Dominican Republic (DR) and the United States (US). Methods We performed a retrospective review of AU and antimicrobial susceptibility patterns from 2019-20 at a hospital in the US (H-US) and the DR (H-DR). Our sites are community teaching hospitals with 151 beds in H-US and 295 beds in H-DR. After AU was tabulated, percent changes between 2019-20 were calculated. Resistance patterns for extended-spectrum beta-lactamase producing (ESBL) E coli, ESBL Klebsiella pneumoniae (ESBL-Kp), carbapenem resistant Pseudomonas aeruginosa (CR-PSAR) and Klebsiella pneumoniae (CR-Kp) were tabulated and percent changes between 2019-20 were calculated. Results AU increased by 10% in H-US and 25% in H-DR, with carbapenem use increasing by 268% and 144% respectively. Ceftriaxone use increased by 30% in H-US and 33% in H-DR. Azithromycin increased 54% in H-US and 338% in the H-DR. Resistance increased from 10% to 28% for ESBL-Kp and from 10% to 12% for ESBL E coli at H-US. CR-PSAR decreased from 20% to 12%, while cefepime and piperacillin resistance increased from 5% to 20% and 3% to 16% respectively (Figure 1). At H-DR, ESBL-Kp resistance decreased from 68% to 64% and increased from 58% to 59% for ESBL E coli. CR-PSAR and cefepime resistance increased from 5% to 19% and from 9% to 29% respectively (Figure 2). Figure 1. Antimicrobial resistance (%) for select organisms at H-US in 2019 and 2020 Figure 2. Antimicrobial resistance (%) for select organisms at H-DR in 2019 and 2020 Conclusion COVID-19 had a major impact on antimicrobial consumption and resistance in the US and DR. A greater impact was seen on ESBL rates in the US whilst a greater impact on carbapenem resistance was seen in the DR. The rise in carbapenem use in H-US reflected a rise in ESBL rates. In the DR, ESBL producing organisms were common prior to COVID-19 and carbapenem use was more widespread. The impact of the COVID-19 pandemic on AU may accelerate AMR worldwide. The scale up of antimicrobial stewardship across the globe is urgently needed to curb AMR. Disclosures All Authors: No reported disclosures

Essential Oil and Hydrophilic Antibiotic Co-Encapsulation in Multiple Lipid Nanoparticles: Proof of Concept and In Vitro Activity against Pseudomonas aeruginosa.

In the worldwide context of an impending emergence of multidrug-resistant bacteria, this research combined the advantages of multiple lipid nanoparticles (MLNs) and the promising therapeutic use of essential oils (EOs) as a strategy to fight the antibiotic resistance of three Pseudomonas aeruginosa strains with different cefepime (FEP) resistance profiles. MLNs were prepared by ultrasonication using glyceryl trioleate (GTO) and glyceryl tristearate (GTS) as a liquid and a solid lipid, respectively. Rosemary EO (REO) was selected as the model EO. REO/FEP-loaded MLNs were characterized by their small size (~110 nm), important encapsulation efficiency, and high physical stability over time (60 days). An assessment of the antimicrobial activity was performed using antimicrobial susceptibility testing assays against selected P. aeruginosa strains. The assays showed a considerable increase in the antibacterial property of REO-loaded MLNs compared with the effect of crude EO, especially against P. aeruginosa ATCC 9027, in which the minimum inhibitory concentration (MIC) value decreased from 80 to 0.6 mg/mL upon encapsulation. Furthermore, the incorporation of FEP in MLNs stabilized the drug without affecting its antipseudomonal activity. Thus, the ability to co-encapsulate an essential oil and a hydrophilic antibiotic into MLN has been successfully proved, opening new possibilities for the treatment of serious antimicrobial infections.

In vitro evolution of cefepime/zidebactam (WCK 5222) resistance in Pseudomonas aeruginosa: dynamics, mechanisms, fitness trade-off and impact on in vivo efficacy.

To study the dynamics, mechanisms and fitness cost of resistance selection to cefepime, zidebactam and cefepime/zidebactam in Pseudomonas aeruginosa. WT P. aeruginosa PAO1 and its ΔmutS derivative (PAOMS) were exposed to stepwise increasing concentrations of cefepime, zidebactam and cefepime/zidebactam. Selected mutants were characterized for change in susceptibility profiles, acquired mutations, fitness, virulence and in vivo susceptibility to cefepime/zidebactam. Mutations were identified through WGS. In vitro fitness was assessed by measuring growth in minimal medium and human serum-supplemented Mueller-Hinton broth. Virulence was determined in Caenorhabditis elegans and neutropenic mice lung infection models. In vivo susceptibility to a human-simulated regimen (HSR) of cefepime/zidebactam was studied in neutropenic mice lung infection. Resistance development was lower for the cefepime/zidebactam combination than for the individual components and high-level resistance was only achieved for PAOMS. Cefepime resistance development was associated with mutations leading to the hyperexpression of AmpC or MexXY-OprM, combined with PBP3 mutations and/or large chromosomal deletions involving galU. Zidebactam resistance was mainly associated with mutations in PBP2. On the other hand, resistance to cefepime/zidebactam required multiple mutations in genes encoding MexAB-OprM and its regulators, as well as PBP2 and PBP3. Cumulatively, these mutations inflicted significant fitness cost and cefepime/zidebactam-resistant mutants (MIC = 16-64 mg/L) remained susceptible in vivo to the HSR. Development of cefepime/zidebactam resistance in P. aeruginosa required multiple simultaneous mutations that were associated with a significant impairment of fitness and virulence.

Distribution of pathogens and antimicrobial resistance in bacteraemia according to hospitalization duration: a nationwide surveillance study in Switzerland

ObjectivesChanging microorganism distributions and decreasing antibiotic susceptibility with increasing length of hospital stay have been demonstrated for the colonization or infection of selected organ systems. We wanted to describe microorganism distribution or antibiotic resistance in bacteraemia according to duration of the hospitalization using a large national epidemiological/microbiological database (ANRESIS) in Switzerland. MethodsWe conducted a nationwide, observational study on bacteraemia using ANRESIS data from 1 January 2008 to 31 December 2017. We analysed data on bacteraemia from those Swiss hospitals that sent information on a regular basis during the entire study period. We described the pathogen distribution and specific trends of resistance during hospitalization for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus. ResultsWe included 28 318 bacteraemia isolates from 90 Swiss hospitals. The most common aetiology was E. coli (33.4%, 9459), followed by S. aureus (16.7%, 4721), K. pneumoniae (7.1%, 2005), Enterococcus faecalis (5.2%, 1473), P. aeruginosa (4.3%, 1228), Streptococcus pneumoniae (4.3%, 1208) and Enterococcus faecium (3.9%, 1101). We observed 489 (1.73%) S. marcescens isolates. We observed an increasing trend for E. faecium (from 1.5% at day 0 to 13.7% at day 30; p < 0.001), K. pneumoniae (from 6.1% to 7.8%, p < 0.001) and P. aeruginosa (from 2.9% to 13.7%, p < 0.001) with increasing duration of hospitalization; and decreasing trends for E. coli (from 41.6% to 21.6%; p < 0.001) and S. aureus (p < 0.001). Ceftriaxone resistance among E. coli remained stable for the first 15 days of hospitalization and then increased. Ceftriaxone resistance among K. pneumoniae and S. marcescens and oxacillin resistance among S. aureus increased linearly during the hospitalization. Cefepime resistance among P. aeruginosa remained stable during the hospitalization. DiscussionWe showed that hospitalization duration is associated with a species- and antibiotic class-dependent pattern of antimicrobial resistance.

Resistance Trends of Klebsiella pneumoniae Causing Urinary Tract Infections in Chongqing, 2011-2019.

PurposeTo analyze the characteristics and trends of drug resistance for Klebsiella pneumoniae (K. pneumoniae), isolated from urinary tract infections (UTIs), to common antibiotics used in clinics.MethodsThis retrospective study was conducted in a teaching hospital in Chongqing from 2011 to 2019. Laboratory data of isolated bacteria were collected and analyzed.ResultsAmong the 17,966 non-repetitive strains isolated from the urine sample, a total of 1543 K. pneumoniae isolates were identified, with an isolation frequency secondary only to Escherichia coli (E. coli) and there was a peak in the K. pneumoniae isolates in the year 2013. During the period, the rate of extended-spectrum β-lactamase (ESBL)-producing K. pneumoniae fell from 48.4% in 2011 to 32.9% in 2019, and a marked jump of resistance was seen in carbapenems from 2.2% to 18.0%. The peak of carbapenem resistance rate (22.6%) to K. pneumoniae was observed in 2017 along with a low ESBL-producing rate (30.9%). Piperacillin/tazobactam and cefepime resistance levels went up from 4.4% to 25.7% and from 18.2% to 30.5%, respectively. Moreover, the K. pneumoniae isolates resistance rate to carbapenems and amikacin gradually grew up, showing their peaks in 2017, and then dropped year by year. However, ceftazidime and aztreonam resistance levels were relatively stable, fluctuating between 21.8% and 35.6%, 32.2% and 39.4%, respectively.ConclusionThere is a significant upward tendency in carbapenem resistance rate and a downward tendency in ESBL-production rate in K. pneumoniae isolates from UTIs, and continuous surveillance is necessary in the future.

Cefepime Versus Cefepime Plus Amikacin as an Initial Antibiotic Choice for Pediatric Cancer Patients With Febrile Neutropenia in an Era of Increasing Cefepime Resistance.

We investigated the treatment outcomes before and after the addition of amikacin to cefepime monotherapy as an initial empirical antibiotic treatment in pediatric cancer patients with febrile neutropenia. This was a retrospective historical cohort study. The subjects were pediatric cancer patients who visited the emergency room at the Samsung Medical Center, Seoul, Korea, due to chemotherapy-induced febrile neutropenia, between January 2011 and December 2016. Since September 2014, the empirical antimicrobial treatment regimen for febrile neutropenia was changed from high-dose cefepime monotherapy to combination therapy of adding a single dose of amikacin. Two hundred twenty-five bacteremia episodes in 164 patients were reported during the study period. Bacteremia caused by cefepime-resistant Gram-negative bacteria was observed in 16% of patients before September 2014 and in 21% of the patients after September 2014 (P = 0.331). Use of appropriate empirical antibiotic treatments increased from 62% to 83% following addition of amikacin to cefepime treatment (P = 0.003). The duration of fever was shorter in the cefepime plus amikacin group than in the cefepime group (22 vs. 34 hours, P = 0.014); however, rates of septic shock and pediatric intensive care unit hospitalizations were not significantly different between the 2 groups (septic shock, both 7%, P = 0.436; pediatric intensive care unit 3% vs. 1%, P = 0.647). We observed no additional benefit of amikacin addition to high-dose cefepime monotherapy. Therefore, adding amikacin to cefepime monotherapy in conditions where cefepime-resistant Gram-negative bacteremia amounts to 20% or less may not be justified.

Fourth Generation Cephalosporin Resistance Among Salmonella enterica Serovar Enteritidis Isolates in Shanghai, China Conferred by blaCTX–M–55 Harboring Plasmids

In this study, we investigated the pattern of antimicrobial resistance in Salmonella enterica serotype Enteritidis isolates in Shanghai, China from 2005 to 2014. We found the first isolates with resistance to the fourth-generation cephalosporin cefepime starting in 2010. Furthermore, we analyzed the epidemic characteristics and mechanisms of underlying cefepime resistance in S. Enteritidis isolates found from 2010. In total, 38 of 2,914 (1.30%) isolates were identified as cefepime-resistant S. Enteritidis (CRSE) isolates by Kirby–Bauer disk diffusion. Two isolates were from animal derived food sources; 36 isolates were from fecal samples of human patients with salmonellosis. Antimicrobial susceptibility testing using the agar dilution method revealed that all CRSE isolates showed additional resistances at least to ceftazidime, cefotaxime, and ampicillin. Additionally, pulsed-field gel electrophoresis (PFGE) profiles indicated that 89.47% of CRSE isolates also displayed similar PFGE patterns. Five types of β-lactamase genes, blaCTX–M (100.00%, 38/38), blaSHV (65.79%, 25/38), blaTEM (52.63%, 20/38), blaACC (18.42%, 7/38), and blaPSE (5.26%, 2/38) were detected by PCR and sequencing. Among blaCTX–M genes, blaCTX–M–55 was the dominant type (84.21%, 32/38). Conjugation and transformation experiments along with plasmid replicon typing revealed that blaCTX–M–55 was located on plasmids of various replicon types with sizes ranging from 76.8 to 138.9 kb. Plasmid sequence analysis also showed that the blaCTX–M–55 gene was mobilized mainly by the ISEcp1-blaCTX–M–55-ORF477 transposition unit and had its own ISEcp1-based promoter, which accelerated the expression and transmission of blaCTX–M–55. Analysis of whole genome sequences (Illumina) of one selected transformant SH12G706-C showed high similarity of the blaCTX–M–55 carrying plasmid with the IncI1 plasmid backbone p628-CTX-M of Klebsiella pneumoniae detected in 2010 in China. The present study demonstrated that the blaCTX–M–55 gene mobilized by ISEcp1- blaCTX–M–55-ORF477 was the main feature shared by CRSE isolates and seems to play an important role for transmission of cefepime resistance. The number of CRSE isolates is rising annually, and the strong dissemination ability of ISEcp1-blaCTX–M–55-ORF477-harboring plasmids among different species represents an important threat to the therapeutic effectiveness of cefepime.

487. Prevalence of Antimicrobial Resistance in Gram-Negative Bacilli Bloodstream Infections at a Tertiary Teaching Hospital in the Dominican Republic

BackgroundBloodstream infections (BSI) with gram-negative bacilli (GNB) are a major cause of morbidity and mortality worldwide. Sepsis due to BSI can carry a mortality rate as high as 40%, with higher mortality in developing nations. Early and appropriate empiric therapeutic selection plays an important role in survival. The rising incidence of antimicrobial resistance (AMR) limits empiric treatment options. Local susceptibility patterns can vary per region, institution or setting. Understanding local AMR may help guide empiric treatment choices. We seek to describe resistance rates for GNB BSI in the Dominican Republic (DR).MethodsThis is a retrospective review of antimicrobial susceptibility patterns from bloodstream infections in a tertiary hospital in the DR. Susceptibility data from all adult inpatient blood cultures were collected from January 1 to December 31, 2017.ResultsA total of 124 blood cultures were reported. The most common organisms were Escherichia coli (43%) and Klebsiella pneumoniae (23%). Fluoroquinolone resistance was present in 70% of E. coli. Phenotypic susceptibility patterns consistent with extended-spectrum β-lactamase (ESBL) producing GNB were present in 46% of isolates. Carbapenem resistance was found in 4 samples and was most common in P. aeruginosa. Susceptibility profile is described on Table 1.ConclusionAMR was high in GNB BSIs in the DR. High rates of ESBL render common cephalosporins sub-optimal for empiric treatment. PTZ retains in vitro susceptibilities despite cefepime resistance but clinical efficacy is controversial. CTX-M ESBLs may cause these resistance pattern in vitro. Further studies are needed to determine genetic mechanisms of resistance. Establishing antimicrobial stewardship programs with rapid diagnostic testing that identify mechanisms of resistance may promote judicious use of carbapenems and reduce further the risk of further development of AMR. Disclosures All authors: No reported disclosures.

Risk factors for cefepime nonsusceptible Gram-negative infections in allogeneic hematopoietic cell transplant recipients.

Allogeneic hematopoietic cell transplant recipients undergo myelosuppressive chemotherapy to allow engraftment of stem cells and are at particularly high risk for bacterial infections and adverse outcomes. Patients undergoing hematopoietic cell transplant are at increased risk for healthcare-associated infections, including infections with multidrug-resistant pathogens. Cefepime is a commonly prescribed antibiotic for empiric therapy in hematopoietic cell transplant patients, but there is minimal data describing cefepime resistance rates, risk factors for resistance, and clinical outcomes associated with cefepime-resistant infections. Adult (≥18 years old) allogeneic hematopoietic cell transplant recipients with a culture positive for a gram-negative rod between January 2010 and January 2016 were spilt into two groups: cefepime susceptible and cefepime nonsusceptible . The primary objective of this study was to identify risk factors for cefepime nonsusceptible through multivariable logistic regression. A total of 107 patients were included (27 cefepime nonsusceptible, 80 cefepime-susceptible), yielding a 25.2% nonsusceptibility rate. Multivariable analysis yielded age >60 years old, Klebsiella spp. infection, Acinetobacter spp. infection, healthcare exposures within 90 days, acute gastrointestinal graft-vs-host-disease, and chronic graft-vs-host-disease at multiple locations as significant risk factors for cefepime nonsusceptible. The receiver operating characteristic area under the curve of the model was 0.851. Thirty-day all-cause mortality (29.6% versus 16.3%, p = 0.13) and length of hospitalization (19 versus 12.5 days, p = 0.0650) were numerically higher in the cefepime nonsusceptible group. Hematopoietic cell transplant patients with acute gastrointestinal graft versus host disease, extensive chronic graft-vs-host-disease, advanced age, previous healthcare exposures, or infections with Klebsiella and Acinetobacter are at increased risk for cefepime nonsusceptible. Patients infected with cefepime nonsusceptible pathogens may have higher rates of mortality and length of hospitalization.

Cephem Potentiation by Inactivation of Nonessential Genes Involved in Cell Wall Biogenesis of β-Lactamase-Producing Escherichia coli.

Reversal of antimicrobial resistance is an appealing and largely unexplored strategy in drug discovery. The objective of this study was to identify potential targets for "helper" drugs reversing cephem resistance in Escherichia coli strains producing β-lactamases. A CMY-2-encoding plasmid was transferred by conjugation to seven isogenic deletion mutants exhibiting cephem hypersusceptibility. The effect of each mutation was evaluated by comparing the MICs in the wild type and the mutant harboring the same plasmid. Mutation of two genes encoding proteins involved in cell wall biosynthesis, dapF and mrcB, restored susceptibility to cefoxitin (FOX) and reduced the MICs of cefotaxime and ceftazidime, respectively, from the resistant to the intermediate category according to clinical breakpoints. The same mutants harboring a CTX-M-1-encoding plasmid fell into the intermediate or susceptible category for all three drugs. Individual deletion of dapF and mrcB in a clinical isolate of CTX-M-15-producing E. coli sequence type 131 (ST131) resulted in partial reversal of ceftazidime and cefepime resistance but did not reduce MICs below susceptibility breakpoints. Growth curve analysis indicated no fitness cost in a ΔmrcB mutant, whereas a ΔdapF mutant had a 3-fold longer lag phase than the wild type, suggesting that drugs targeting DapF may display antimicrobial activity, in addition to synergizing with selected cephems. DapF appeared to be a potential FOX helper drug target candidate, since dapF inactivation resulted in synergistic potentiation of FOX in the genetic backgrounds tested. The study showed that individual inactivation of two nonessential genes involved in cell wall biogenesis potentiates cephem activity according to drug- and strain-specific patterns.

The differential importance of mutations within AmpD in cephalosporin resistance of Enterobacter aerogenes and Enterobacter cloacae

Mechanisms leading to carbapenem and cephalosporin resistance were sought in Enterobacter aerogenes isolates that were highly resistant to carbapenems but had no known carbapenemase. Results were compared with recent work examining carbapenem-resistant Enterobacter cloacae. Eighteen carbapenem-resistant E. aerogenes were screened for known β-lactamase and carbapenemase genes, and novel carbapenemases were sought in whole-genome sequencing (WGS) data of the three most resistant isolates. For all isolates, ampC, ampR, ampD and the porin genes omp35 and omp36 were investigated by Sanger sequencing or from available WGS data. Expression of ampC and porin genes was measured in comparison with cephalosporin- and carbapenem-susceptible control strains by reverse transcriptase PCR, with porin translation also detected by SDS-PAGE. Loss of Omp35, primarily due to decreased transcription (up to 250×), was observed in ertapenem-resistant isolates (MICs ≥ 2 mg/L), whereas meropenem resistance (MICs ≥ 4 mg/L) was observed in those isolates also showing decreased or no production of Omp36. Loss of Omp36 was due to combinations of premature translation termination or reduced transcription. In contrast to E. cloacae, cephalosporin resistance in E. aerogenes was not associated with lesions in AmpD. High-level cefepime resistance (MIC = 32 mg/L) was caused by a novel modification in the H-10 helix of AmpC in one isolate. The differential importance of AmpD lesions in cephalosporin resistance in E. cloacae and E. aerogenes underlines the differences between these contrasting members of the Enterobacter genus. Porin loss resulted in high-level carbapenem resistance with gradual loss of Omp36, which led to high-level meropenem resistance.

A study on detection of extended-spectrum beta-lactamases (ESBLs) and comparison of various phenotypic methods of AmpC detection in Pseudomonas aeruginosa from various clinical isolates in a tertiary care teaching hospital

Introduction: Pseudomonas aeruginosa is one of the major etiological agents of nosocomial infection. They are difficult to treat as the majority of them exhibit varying degrees of innate resistance. Acquired resistance is mediated by the production of chromosomal and plasmid-mediated AmpC beta-lactamases, extended-spectrum beta-lactamases (ESBLs), and metallo-beta-lactamases (MBLs). Objectives: This study was conducted for the detection of ESBLs and the comparison of various phenotypic methods of AmpC beta-lactamases (both inducible and plasmid-mediated) from various clinical isolates of Pseudomonas aeruginosa. Materials and Methods: A prospective study was conducted for a period of 6 months from January 2014 to June 2014. Isolates of Pseudomonas aeruginosa were tested for ESBLs by combined disk diffusion method using ceftazidime/ceftazidime+clavulanic acid (CAZ+CAC). Inducible AmpC beta-lactamases were detected by both ceftazidime-imipenem antagonism test (CIAT) and cefotaxime/cefoxitin (CTX/CX) inducible disk diffusion test. Plasmid-mediated AmpC were detected using AmpC disk test and ethylenediaminetetraacetic acid (EDTA) disk test. All the isolates were tested for cefepime resistance. Results: Out of 116 Pseudomonas aeruginosa isolates, 70 were ceftazidime-resistant. While ESBLs were observed in 67 out of 70 isolates, 36 were positive for inducible AmpC by both the methods. Plasmid-mediated AmpC were detected in only 8 isolates. All the 70 strains showed resistance to cefepime. Conclusions: High prevalence of ESBL and chromosomal-mediated AmpC was observed in Pseudomonas aeruginosa. Both the inducible disk diffusion tests (CIAT, CTX/CX) were equally effective in the detection of inducible AmpC. As Pseudomonas is one of the major nosocomial pathogens, such high resistance poses a grave threat.

In Vivo Evolution of CMY-2 to CMY-33 β-Lactamase in Escherichia coli Sequence Type 131: Characterization of an Acquired Extended-Spectrum AmpC Conferring Resistance to Cefepime

Cefepime is frequently prescribed to treat infections caused by AmpC-producing Gram-negative bacteria. CMY-2 is the most common plasmid-mediated AmpC (pAmpC) β-lactamase. Unfortunately, CMY variants conferring enhanced cefepime resistance have been reported. Here, we describe the evolution of CMY-2 to an extended-spectrum AmpC (ESAC) in clonally identical Escherichia coli isolates obtained from a patient. The CMY-2-producing E. coli isolate (CMY-2-Ec) was isolated from a wound. Thirty days later, one CMY-33-producing E. coli isolate (CMY-33-Ec) was detected in a bronchoalveolar lavage fluid sample. Two weeks before the isolation of CMY-33-Ec, the patient received cefepime. CMY-33-Ec and CMY-2-Ec were identical by repetitive extragenic palindromic-PCR (rep-PCR), being of hyperepidemic sequence type 131 (ST131) but showing different β-lactam MICs (e.g., cefepime MIC, 16 and ≤ 0.5 μg/ml for CMY-33-Ec and CMY-2-Ec, respectively). Identical CMY-2-Ec isolates were also found in a rectal swab. CMY-33 differs from CMY-2 by a Leu293-Ala294 deletion. Expressed in E. coli strain DH10B, both CMYs conferred resistance to ceftazidime (≥ 256 μg/ml), but the cefepime MICs were higher for CMY-33 than CMY-2 (8 versus 0.25 μg/ml, respectively). The kcat/Km or inhibitor complex inactivation (kinact)/Ki app (μM(-1) s(-1)) indicated that CMY-33 possesses an extended-spectrum β-lactamase (ESBL)-like spectrum compared to that of CMY-2 (e.g., cefoxitin, 0.2 versus 0.4; ceftazidime, 0.2 versus not measurable; cefepime, 0.2 versus not measurable; and tazobactam, 0.0018 versus 0.0009, respectively). Using molecular modeling, we show that a widened active site (∼ 4-Å shift) may play a significant role in enhancing cefepime hydrolysis. This is the first in vivo demonstration of a pAmpC that under cephalosporin treatment expands its substrate spectrum, resembling an ESBL. The prevalence of CMY-2-Ec isolates is rapidly increasing worldwide; therefore, awareness that cefepime treatment may select for resistant isolates is critical.