Molecular epidemiology and characterization of multiple drug-resistant (MDR) clinical isolates of Acinetobacter baumannii

High-throughput single-cell analysis reveals Omp38-specific monoclonal antibodies that protect against Acinetobacter baumannii infection

Infections caused by Acinetobacter baumannii (A. baumannii) have emerged as a global public health concern because of high pathogenicity of this bacterium. Monoclonal antibodies (mAbs) have a lower likelihood of promoting drug resistance and offer targeted treatment, thereby reducing potential adverse effects; however, the therapeutic potential of mAbs targeting A. baumannii has not been fully characterized. In this study, mAbs against the outer membrane proteins (OMPs) of A. baumannii were isolated in a high-throughput manner. The ability of Omp38-specific mAbs to bind to A. baumannii strains from diverse sources was confirmed via enzyme-linked immunosorbent assay (ELISA). Intravenous administration of the Omp38-specific mAbs significantly improved the survival rate and reduced the bacterial load in a mouse model of lethal A. baumannii infection. Flow cytometry and ELISA confirmed that immune cell infiltration and cytokine production, respectively, decreased in a mouse model of sublethal A. baumannii infection. In addition, analysis of the Omp38-mAb C3 binding conformation revealed the potential mechanism of broad-spectrum binding activity of this mAb against A. baumannii. Taken together, these findings indicate that mAbs against Omp38 facilitate bacterial clearance from host, minimize inflammatory mediator release and reduce host damage, highlighting the potential of Omp38-specific mAbs in the clinical treatment of A. baumannii infection.

Diverse Acinetobacter species and Plasmid-Driven spread of carbapenem resistance in pharmaceutical settings in China

Acinetobacter species have emerged as a significant public health concern due to their remarkable capacity to acquire antimicrobial resistance. Environmental reservoirs play a crucial role in spreading antimicrobial resistance genes and potentially pathogenic bacteria to clinical settings. However, most studies on nonhuman isolates have focused on a limited sample size. Comprehensive population sampling on One Health principles is essential to monitor the antibiotic resistome and virulome in Acinetobacter spp. Here, we identified three carbapenems-resistant Acinetobacter spp. isolates harboring blaNDM-1 and discovered two novel Acinetobacter species in pharmaceutical production environments. A total of 94 Acinetobacter spp. strains were isolated from pharmaceutical production environments across 17 cities in China, forming 17 distinct Acinetobacter clusters comprising two novel species and 15 previously known species. Phylogenetic analysis indicated that Acinetobacter spp. isolated from pharmaceutical settings are predominantly confined to these settings. Genomic analysis revealed 10 specific families of blaCHDL genes in 51 isolates and blaNDM-1 in three isolates. The overall rates of phenotypic resistance to antimicrobials were low among Acinetobacter spp. isolates, with less than 10 % resistance observed for all tested drugs, and only three isolates carrying blaNDM-1 were resistant to carbapenems. The blaNDM-1 gene was located in approximately 49 kb PTU-Pse8 conjugative plasmids with conserved backbones, although plasmid pXH1688-NDM displayed enhanced growth and stability. Two novel Acinetobacter species, A. yuyunsongii sp. nov. and A. chenhuanii sp. nov., were characterized using phenotypic and genomic analyses. Particularly, A. yuyunsongii sp. nov. XH1639 harbors a blaOXA-58-carrying conjugative plasmid and exhibits multidrug-resistant phenotype. Our study advances Acinetobacter taxonomy and underscores the urgency of monitoring the dynamics of Acinetobacter species in environmental sources to implement effective measures to mitigate transmission risks to healthcare facilities.

Genetic profiling of multidrug-resistant Acinetobacter baumannii from a tertiary care center in Malaysia

Genetic characterization of multidrug-resistant (MDR) Acinetobacter baumannii remains scarce in Malaysia. This study aimed to characterize antibiotic resistance, genomic location, and genetic relatedness among the A. baumannii isolates obtained from a tertiary hospital in Malaysia. A total of 128 MDR A. baumannii isolates were collected from patients admitted to various wards (intensive care unit [ICU], neonatal intensive care unit, coronary care unit, high dependency ward [HDW], and general wards). The isolates were identified by Vitek 2 and PCR amplification of the 16S rRNA gene followed by sequencing. The isolates were tested against imipenem, ceftazidime, amikacin, gentamicin, ampicillin, and ciprofloxacin using disk diffusion, Epsilometer test, and broth microdilution. The antibiotic resistance genes, blaOXA-23, blaOXA-24, blaADC, blaVIM, and blaIMP, were detected in chromosomal and plasmid DNA using PCR. Insertion sequence ISAba1/blaOXA-23 gene was detected on chromosomal DNA only. Isolates with different antibiotic susceptibility patterns and PCR profiles were subjected to multi-locus sequence typing. MDR A. baumannii was predominantly found in HDW (39.84%), general wards (29.69%), and ICU (28.13%). All isolates conferred resistance to carbapenem and more than 90% resistance to the remaining antibiotics. The antibiotic resistance genes blaOXA-23, blaVIM, and blaADC were detected in both chromosomal and plasmid DNA. The ISAba1/blaOXA-23 gene was detected in 99.22% of the isolates. Four sequence types (STs) were distinguished: ST2 (76.67%), ST164 (10%), ST642 (10%), and ST643 (3.33%). ST164 and ST642 were unique and represent a significant finding in Malaysia's surveillance data. These STs are associated with acquired blaOXA-23, indicating an evolutionary adaptation of A. baumannii within the hospital setting.IMPORTANCEAcinetobacter baumannii is a ubiquitous Gram-negative coccobacillus bacterium that is primarily associated with nosocomial infections that can colonize biotic and abiotic surfaces to enhance cell-to-cell adhesion, ensuring the establishment of infections. To date, the spread of multidrug-resistant A. baumannii (MDRAB) has become rampant and a great concern in the hospital setting, as the available antibiotics are insufficient to treat infections. The antibiotic resistance island resides in a mobile element and rapidly evolved. The antibiotic susceptibility data with its resistance mechanisms would contribute to and facilitate the management and infection control caused by MDRAB.

Molecular insights into antimicrobial resistant Staphylococcus aureus strains: A potential zoonosis of goat origin

Antimicrobial-resistant (AMR) Staphylococcus aureus (S. aureus) strains have attained global attention due to their life-threatening zoonotic nature. Being a member of ESKAPE group, S. aureus has an ability to escape the biocidal action of antimicrobial drugs. The current study investigated the prevalence and molecular characterization of methicillin-resistant S. aureus (MRSA), β-lactam-resistant S. aureus (BRSA), aminoglycoside-resistant S. aureus (ARSA), tetracycline-resistant S. aureus (TRSA), and fluoroquinolones-resistant S. aureus (FRSA) associated with goat subclinical mastitis (SCM). Furthermore, the antimicrobial resistance and susceptibility profile of various antibiotics and non-antibiotics (NSAIDs, nisin, N-acetylcysteine, vitamin-C) along with their possible role in modulating the antibiotic resistance of MDR isolates was also investigated. A total of 768 goat milk samples were subjected to California mastitis test for SCM followed by bacteriological and molecular characterization of S. aureus. Moreover, in-vitro susceptibility of resistant antibiotics, non-antibiotics, and their combination against MDR S. aureus were conducted through well diffusion and broth microdilution assays. The results depicted that 55.47 % and 26.82 % of milk samples were positive for SCM and S. aureus, respectively. The molecular assay confirmed 35.92 % of isolates as MRSA, 45.63 % as BRSA, 50.49 % as ARSA, and 32.52 % but no isolate was confirmed as FRSA on molecular basis. The multidrug resistance was observed in 62.13 % and 47.09 % isolates, respectively. Molecular characterized MDR S. aureus revealed high homology of study isolates with the isolates of neighboring countries like India, Korea, Iran, and China. Antimicrobial susceptibility trials on well diffusion assay showed higher efficacy of different non-antibiotics with resistant antibiotics as penicillin with ketoprofen and gentamicin with flunixin meglumine while oxytetracycline with N-acetylcystiene. The synergy testing by checkerboard assay revealed synergistic activity of penicillin with ketoprofen, gentamicin with flunixin meglumine, and oxytetracycline with N-acetylcysteine. The current study highlighted the emergence and spread of AMR S. aureus strains from goat SCM and provided insights into possible drug repurposing of various non-antibiotics to modulate the multidrug resistance of S. aureus which will be helpful in devising the therapeutic options and control measures for this pathogen.

Current treatment strategies for targeting virulence factors and biofilm formation in Acinetobacter baumannii

A higher prevalence of Acinetobacter baumannii infections and mortality rate has been reported recently in hospital-acquired infections (HAI). The biofilm-forming capability of A. baumannii makes it an extremely dangerous pathogen, especially in device-associated hospital-acquired infections (DA-HAI), thereby it resists the penetration of antibiotics. Further, the transmission of the SARS-CoV-2 virus was exacerbated in DA-HAI during the epidemic. This review specifically examines the complex interconnections between several components and genes that play a role in the biofilm formation and the development of infections. The current review provides insights into innovative treatments and therapeutic approaches to combat A. baumannii biofilm-related infections, thereby ultimately improving patient outcomes and reducing the burden of HAI.

Population pharmacokinetics and humanized dosage regimens matching the peak, area, trough, and range of amikacin plasma concentrations in immune-competent murine bloodstream and lung infection models

Amikacin is an FDA-approved aminoglycoside antibiotic that is commonly used. However, validated dosage regimens that achieve clinically relevant exposure profiles in mice are lacking. We aimed to design and validate humanized dosage regimens for amikacin in immune-competent murine bloodstream and lung infection models of Acinetobacter baumannii. Plasma and lung epithelial lining fluid (ELF) concentrations after single subcutaneous doses of 1.37, 13.7, and 137 mg/kg of body weight were simultaneously modeled via population pharmacokinetics. Then, humanized amikacin dosage regimens in mice were designed and prospectively validated to match the peak, area, trough, and range of plasma concentration profiles in critically ill patients (clinical dose: 25-30 mg/kg of body weight). The pharmacokinetics of amikacin were linear, with a clearance of 9.93 mL/h in both infection models after a single dose. However, the volume of distribution differed between models, resulting in an elimination half-life of 48 min for the bloodstream and 36 min for the lung model. The drug exposure in ELF was 72.7% compared to that in plasma. After multiple q6h dosing, clearance decreased by ~80% from the first (7.35 mL/h) to the last two dosing intervals (~1.50 mL/h) in the bloodstream model. Likewise, clearance decreased by 41% from 7.44 to 4.39 mL/h in the lung model. The humanized dosage regimens were 117 mg/kg of body weight/day in mice [administered in four fractions 6 h apart (q6h): 61.9%, 18.6%, 11.3%, and 8.21% of total dose] for the bloodstream and 96.7 mg/kg of body weight/day (given q6h as 65.1%, 16.9%, 10.5%, and 7.41%) for the lung model. These validated humanized dosage regimens and population pharmacokinetic models support translational studies with clinically relevant amikacin exposure profiles.

Sub-minimum inhibitory concentrations (sub-MICs) of colistin on Acinetobacter baumannii biofilm formation potency, adherence, and invasion to epithelial host cells: an experimental study in an Iranian children's referral hospital

Here, we described the efficacy of colistin sub-minimum inhibitory concentrations (sub-MICs) on biofilm-forming activity, host epithelial cell adherence, and invasion capacity of Acinetobacter baumannii strains collected from children admitted to the Children's Medical Center Hospital. Biofilm formation potency of A. baumannii clinical isolates was measured using a 96-well microtiter plate assay. Distribution of biofilm-related genes, including bap, abaI, ompA, csuE, and blaPER-1, was detected by PCR. The mRNA expression level of ompA and csuE was measured by qPCR in the presence of ¼ and ½ MICs of colistin. A. baumannii adhesion and invasion to eukaryotic host cells were phenotypically assayed at sub-MICs of colistin. Eighty percent (56/70) and 35.7% (25/70) of A. baumannii isolates were multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes, respectively. The strong, moderate, and weak biofilm producers of A. baumannii were 37.1% (26/70), 32.8%, (23/70), and 22.8% (16/70), respectively. The frequencies of biofilm-associated genes were 100% for abaI, ompA, and csuE, followed by 22.8% (16/70) and 24.3% (17/70) for bap and blaPER-1, respectively. The downregulation of csuE and ompA expression levels was observed in the sub-MIC of colistin. In vitro cell culture study showed a decreased capability of A. baumannii to adhere to the human epithelial cells at sub-inhibitory doses of colistin; however, none of the isolates could invade HEp-2 cells. Our study showed that the genes encoding biofilm-associated proteins undergo downregulation in expression levels after exposure to sub-MICs of colistin in A. baumannii. Longitudinal in vivo studies are needed to fully understand the clinical aspects of pathogenicity mechanisms and evolutionary dynamics of drug resistance.IMPORTANCESince the toxicity of colistin is dose dependent, there is a focus on strategies that reduce the dose while maintaining the therapeutic effect of the drug. Our findings about sub-inhibitory doses of colistin provide a novel insight into the logical use of colistin to treat and control Acinetobacter baumannii-related infections in clinical practice.

Dynamic monitoring of neutrophil/lymphocyte ratio, APACHE II score, and SOFA score predict prognosis and drug resistance in patients with Acinetobacter baumannii-calcoaceticus complex bloodstream infection: a single-center retrospective study

Objective

This study aimed to evaluate the clinical value of dynamic monitoring of neutrophil/lymphocyte ratio (NLR), APACHE II (Acute Physiology and Chronic Health Evaluation II) score, and Sequential Organ Failure Assessment (SOFA) score in predicting 28-day prognosis and drug resistance in patients with bloodstream infection with Acinetobacter baumannii-calcoaceticus complex (Abc complex).

Patients and methods

In this research, individuals admitted to Tianjin Medical University General Hospital from January 2017 to March 2023 with bloodstream infections and a minimum of one Abc complex positive blood culture were chosen. The risk factors for the 28-day prognosis and drug resistance were analyzed using logistic regression. The NLR, APACHE II score, and SOFA score were evaluated for predicting 28-day prognosis and drug resistance using an ROC curve analysis. The data were analyzed using R Studio to find correlations and conduct survival analysis with the Kaplan-Meier method.

Results

The final statistical analysis included a total of 129 patients with bloodstream infections caused by Abc complex. Independent risk factors predicting mortality within 28 days were identified as follows: the SOFA score and APACHE II scores at 24 h, and APACHE II scores at 72 h after the onset of blood infection (p < 0.05). NLR, SOFA score, and APACHE II score did not predict drug resistance. Patients with Carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (CRAB) had shorter survival times than those with carbapenem-sensitive strains (40.77 days vs. 47.65 days, respectively, p = 0.0032).

Conclusion

The prognosis of Abc complex bloodstream infection is affected by both SOFA and APACHE II scores. Both scoring systems have similar prognostic values at different time points after infection, but for computational convenience, it is recommended to use the SOFA score. NLR exhibits limited effectiveness in predicting mortality within 28 days. Carbapenem-resistant individuals with Abc complex experience significantly reduced survival time. None of the three factors-SOFA score, APACHE II score, and NLR-can early predict the occurrence of CRAB infections effectively.

Individual Components of Polymyxin B Modeled via Population Pharmacokinetics to Design Humanized Dosage Regimens for a Bloodstream and Lung Infection Model in Immune-Competent Mice

Polymyxin B is a "last-line-of-defense" antibiotic approved in the 1960s. However, the population pharmacokinetics (PK) of its four main components has not been reported in infected mice. We aimed to determine the PK of polymyxin B1, B1-Ile, B2, and B3 in a murine bloodstream and lung infection model of Acinetobacter baumannii and develop humanized dosage regimens. A linear 1-compartment model, plus an epithelial lining fluid (ELF) compartment for the lung model, best described the PK. Clearance and volume of distribution were similar among the four components. The bioavailability fractions were 72.6% for polymyxin B1, 12.0% for B1-Ile, 11.5% for B2, and 3.81% for B3 for the lung model and were similar for the bloodstream model. While the volume of distribution was comparable between both models (17.3 mL for the lung and ~27 mL for the bloodstream model), clearance was considerably smaller for the lung (2.85 mL/h) compared to that of the bloodstream model (5.59 mL/h). The total drug exposure (AUC) in ELF was high due to the saturable binding of polymyxin B presumably to bacterial lipopolysaccharides. However, the modeled unbound AUC in ELF was ~16.7% compared to the total drug AUC in plasma. The long elimination half-life (~4 h) of polymyxin B enabled humanized dosage regimens with every 12 h dosing in mice. Daily doses that optimally matched the range of drug concentrations observed in patients were 21 mg/kg for the bloodstream and 13 mg/kg for the lung model. These dosage regimens and population PK models support translational studies for polymyxin B at clinically relevant drug exposures.

Extended-Spectrum β-Lactamases (ESBL) Producing Bacteria in Animals

Animals have been identified as potential reservoirs and vectors of resistance genes, with studies showing that Gram-negative bacteria can acquire resistance through the horizontal transmission of resistance genes on plasmids. It is important to understand the distribution of antimicrobial-resistant bacteria and their drug-resistant genes in animals. Previous review articles mostly focused on a single bacterium or a single animal. Our objective is to compile all ESBL-producing bacteria isolated from various animals in recent years and provide a comprehensive viewpoint. Using a thorough PubMed literature search spanning from 1 January 2020 to 30 June 2022, studies exploring extended-spectrum beta-lactamase (ESBL) producing bacteria in animals were included. ESBL-producing bacteria are present in animals from various countries around the world. The most common sources of these bacteria were farm animals, and the most frequently isolated bacteria were Escherichia coli and Klebsiella pneumoniae. The most detected ESBL genes were blaTEM, blaSHV, and blaCTX-M. The presence of ESBL-producing bacteria in animals highlights the importance of the One Health approach to address the issue of antibiotic resistance. Further research is needed to better understand the epidemiology and mechanisms of the spread of ESBL-producing bacteria in animal populations and their potential impact on human and animal health.

Penicillin Binding Protein 7/8 Is a Potential Drug Target in Carbapenem-Resistant Acinetobacter baumannii

Limited therapeutic options dictate the need for new classes of antimicrobials active against carbapenem-resistant Acinetobacter baumannii. Presented data confirm and extend penicillin binding protein 7/8 (PBP 7/8) as a high-value target in the CR A. baumannii strain HUMC1. PBP 7/8 was essential for optimal growth/survival of HUMC1 in ex vivo human ascites and in a rat subcutaneous abscess model; in a mouse pneumonia model, the absence of PBP 7/8 decreased lethality 11-fold. The loss of PBP 7/8 resulted in increased permeability, sensitivity to complement, and lysozyme-mediated bactericidal activity. These changes did not appear to be due to alterations in the cellular fatty acid composition or capsule production. However, a decrease in lipid A and an increase in coccoidal cells and cell aggregation were noted. The compromise of the stringent permeability barrier in the PBP 7/8 mutant was reflected by an increased susceptibility to several antimicrobials. Importantly, expression of ampC was not significantly affected by the loss of PBP 7/8 and serial passage of the mutant strain in human ascites over 7 days did not yield revertants possessing a wild-type phenotype. In summary, these data and other features support PBP 7/8 as a high-value drug target for extensively drug-resistant and CR A. baumannii. Our results guide next-stage studies; the determination that the inactivation of PBP 7/8 results in an increased sensitivity to lysozyme enables the design of a high-throughput screening assay to identify small molecule compounds that can specifically inhibit PBP 7/8 activity.

Acinetobacter nosocomialis Causes as Severe Disease as Acinetobacter baumannii in Northeast Thailand: Underestimated Role of A. nosocomialis in Infection

Infections by Acinetobacter species are recognized as a serious global threat due to causing severe disease and their high levels of antibiotic resistance. Acinetobacter baumannii is the most prevalent pathogen in the genus, but infection by Acinetobacter nosocomialis has been reported widely. Diagnosis of patients with A. baumannii infection is often misdiagnosed with other Acinetobacter species, especially A. nosocomialis. This study investigated whether there were significant differences in clinical outcomes between patients infected with A. baumannii versus A. nosocomialis in Northeast Thailand, and to characterize serological responses to infection with these pathogens. The results show that A. baumannii had higher levels of multidrug resistance. Despite this, clinical outcomes for infection with A. baumannii or A. nosocomialis were similar with mortalities of 33% and 36%, respectively. Both pathogens caused community-acquired infections (A. baumannii 35% and A. nosocomialis 29% of cases). Plasma from uninfected healthy controls contained IgG antibody that recognized both organisms, and infected patients did not show a significantly enhanced antibody response from the first week versus 2 weeks later. Finally, the patterns of antigen recognition for plasma IgG were similar for patients infected with A. baumannii or A. nosocomialis infection, and distinct to the pattern for patients infected with non-Acinetobacter. In conclusion, our data revealed that infection with A. nosocomialis was associated with a similarly high level of mortality as infection with A. baumannii, the high rate of community-acquired infection and antibodies in uninfected individuals suggesting that there is significant community exposure to both pathogens. IMPORTANCE Bacterial infections by Acinetobacter species are global threats due to their severity and high levels of antibiotic resistance. A. baumannii is the most common pathogen in the genus; however, infection by A. nosocomialis has also been widely reported but is thought to be less severe. In this study, we have prospectively investigated 48 reported cases of A. baumannii infection in Northeast Thailand, and characterized the serological responses to infection. We found that 14 (29%) of these infections were actually caused by A. nosocomialis. Furthermore, the incidence of antibiotic resistance among A. nosocomialis strains, APACHE II scores, and mortality for patients infected with A. nosocomialis were much higher than published data. Both A. baumannii and A. nosocomialis had unexpectedly mortality rates of over 30%, and both pathogens caused a high rate of community-acquired infections. Importantly, background antibodies in uninfected individuals suggest significant community exposure to both pathogens in the environment.

Antibiotic resistance and carriage class I integron in clinical isolates of Acinetobacter baumannii from Al Muthanna, Iraq

The goal of this work was to systematically characterize and detect class 1, 2, and 3 integrons with many antibiotic resistance A. baumannii strains collected from a clinical environment in Iraq's Al-Muthanna hospitals. In this investigation, 24 non-replicated clinical strains of A. baumannii were evaluated using Chrome agar as a selective medium and PCR of the rplB gene. The clonal relatedness of the isolates to class 1 integron was evaluated using a PCR technique. The prevalence of class 1 integron was detected by PCR in only 12 clones of A. baumannii followed by HinfI digestion analysis showing three identical bands at 160 bp, 1350 bp, and 870 bp. In addition, PCR sequencing confirmed the presence of gene cassette arrays consisting of aacA4-catB8-aadA1 (100%) in class 1 integron. The sequence analysis of the integron shows 97.87 identity with A. baumannii isolates from Australia (GenBank accession number CP054302) among A. baumannii isolates. The blast analysis of this class I integron showed that the presence of the intI1, aacA4-catB8-aadA1 genes can considerably boost the acquisition of MDR phenotypes in A. baumannii isolates. We concluded that antibiotics of many types are widely used. The presence of integrons in A. baumannii is concerning for public health. In the clinical setting, it appears that the class 1 integron can be used as a predictive biomarker for the presence of MDR phenotypes. In these bacteria, however, the integron does not possess carbapenemases genes.

Molecular Epidemiology of Clinical Carbapenem-Resistant Acinetobacter baumannii-calcoaceticus complex Isolates in Tertiary Care Hospitals in Java and Sulawesi Islands, Indonesia

Carbapenem-resistant Acinetobacter baumannii (A. baumannii)-calcoaceticus complex (CRAb-cc) is an important pathogen causing nosocomial infections worldwide; however, molecular epidemiology of the A. baumannii-calcoaceticus complex in Indonesian hospitals is scarce. This study aimed to determine the clonal relatedness of CRAb-cc in two tertiary care hospitals in Malang and Manado in Indonesia. The CRAb-cc isolates from routine clinical cultures in two tertiary care hospitals in Malang and Manado were identified using the Vitek2^® system (bioMérieux, Lyon, France). Multi-locus variable-number tandem-repeat analysis (MLVA) typing, multi-locus sequence typing (MLST), clonal complex (CC), and phylogenetic tree analysis were conducted for a subset of isolates. Seventy-three CRAb-cc isolates were collected. The CRAb-cc isolates were frequently found among lower-respiratory-tract specimens. We detected the MLVA type (MT) 1, MT3, and MT4 CRAB-cc isolates belonging to the sequence type (ST) 642, and CC1 was the predominant clone in this study. In conclusion, we identified the clonal relatedness of A. baumannii-calcoaceticus complex isolates in two tertiary care hospitals in Malang and Manado in Indonesia. Further study is required to investigate the clinical importance and distribution of ST642 in Indonesian hospitals for developing prevention and control measures.

Molecular Characterization of ESBLs and QnrS Producers From Selected Enterobacteriaceae Strains Isolated From Commercial Poultry Production Systems in Kiambu County, Kenya

Background

The emergence and spread of Extended-spectrum β-lactamases (ESBLs) in Enterobacteriaceae through the plasmid-mediated exchange have become a major threat to public health by complicating the treatment of severe infections in both animals and humans. Therefore, the current study focused on evaluating the manifestation of ESBLs production from the fecal isolates of E. coli, Shigella spp, Salmonella spp, and Klebsiella spps in commercial poultry production systems of Kiambu County, Kenya.

Materials and methods

Out of 591 isolates identified as E. coli, Shigella spp, Salmonella spp, and Klebsiella spps from 437 fecal samples, only 78 were phenotypically suggestive to be ESBL producers. The possible ESBL producers were screened for the presence of ^blaTEM, ^blaCTX-M, ^blaOXA, and ^blaSHV using the PCR technique. These isolates were also screened for carriage of the QnrS gene that confers resistance to the fluoroquinolone class of drugs.

Results

The most detected ESBL gene from the isolates was ^blaOXA (n = 20; 26%), followed by ^blaTEM (n = 16, 21%), with the majority of them detected in E. coli. The ^blaCTX-M was identified in all the 4 enteric's bacteria-type isolates tested. Three E. coli and Salmonella spp respectively were found to harbor all the 5 antimicrobial resistance (AMR) gene types. The ^blaTEM, ^blaOXA, ^blaSHV, and QnrS genes were not detected from Klebsiella and Shigella spps. Additionally, most of the AMR gene co-carriage was detected in both E. coli and Salmonella spps as follows ^blaTEM + ^blaOXA (n = 4); ^blaTEM + QnrS (n = 3); ^blaTEM + ^blaOXA + QnrS (n = 3), concurrently.

Conclusion

Our findings highlight the significance of commercial poultry production in disseminating transferable antibiotic resistance genes that act as potential sources of extensive drug resistance in livestock, humans, and the environment, leaving limited therapeutic options in infection management.

Virulence Characteristics of Biofilm-Forming Acinetobacter baumannii in Clinical Isolates Using a Galleria mellonella Model

Acinetobacter baumannii is a Gram-negative coccobacillus responsible for severe hospital-acquired infections, particularly in intensive care units (ICUs). The current study was designed to characterize the virulence traits of biofilm-forming carbapenem-resistant A. baumannii causing pneumonia in ICU patients using a Galleria mellonella model. Two hundred and thirty patients with hospital-acquired or ventilator-associated pneumonia were included in our study. Among the total isolates, A. baumannii was the most frequently isolated etiological agent in ICU patients with pneumonia (54/165, 32.7%). All A. baumannii isolates were subjected to antimicrobial susceptibility testing by the Kirby–Bauer disk diffusion method, while the minimum inhibitory concentrations of imipenem and colistin were estimated using the broth microdilution technique. The biofilm formation activity of the isolates was tested using the microtiter plate technique. Biofilm quantification showed that 61.1% (33/54) of the isolates were strong biofilm producers, while 27.7% (15/54) and 11.1% (6/54) showed moderate or weak biofilm production. By studying the prevalence of carbapenemases-encoding genes among isolates, bla_OXA-23-_like was positive in 88.9% of the isolates (48/54). The Bla_NDM gene was found in 27.7% of the isolates (15/54 isolates). Bla_OXA-23-_like and bla_NDM genes coexisted in 25.9% (14/54 isolates). Bap and bla_PER-1 genes, the biofilm-associated genes, coexisted in 5.6% (3/54) of the isolates. For in vivo assessment of A. baumannii pathogenicity, a Galleria mellonella survival assay was used. G. mellonella survival was statistically different between moderate and poor biofilm producers (p < 0.0001). The killing effect of the strong biofilm-producing group was significantly higher than that of the moderate and poor biofilm producers (p < 0.0001 for each comparison). These findings highlight the role of biofilm formation as a powerful virulence factor for carbapenem-resistant A. baumannii that causes pneumonia in the ICU.

Comparative analysis of carbapenemases, RND family efflux pumps and biofilm formation potential among Acinetobacter baumannii strains with different carbapenem susceptibility

Aim

This study has conducted a comparative analysis of common carbapenemases harboring, the expression of resistance-nodulation-cell division (RND) family efflux pumps, and biofilm formation potential associated with carbapenem resistance among Acinetobacter baumannii (A. baumannii) strains with different carbapenem susceptibility. Methods: A total of 90 isolates of A. baumannii from two tertiary hospitals of China were identified and grouped as carbapenem susceptible A. baumannii (CSAB) strains and carbapenem non-susceptible A. baumannii (CnSAB) strains based on the susceptibility to imipenem. Harboring of carbapenemase genes, relative expression of RND family efflux pumps and biofilm formation potential were compared between the two groups. Result: Among these strains, 12 (13.3 %) strains were divided into the CSAB group, and 78 (86.7 %) strains into the CnSAB group. Compared with CSAB strains, CnSAB strains increased distribution of bla_OXA−23 (p < 0.001) and ISAba1/bla_{OXA−51−like} (p = 0.034) carbapenemase genes, and a 6.1-fold relative expression of adeB (p = 0.002), while CSAB strains led to biofilm formation by 1.3-fold than CnSAB strains (p = 0.021).

Conclusions

Clinically, harboring more bla_{OXA−23−like} and ISAba1/bla_{OXA−51−like} complex genes and overproduction of adeABC are relevant with carbapenem resistance, while carbapenem susceptible strains might survive the stress of antibiotic through their ability of higher biofilm formation.

Analysis of blaCHDL Genes and Insertion Sequences Related to Carbapenem Resistance in Acinetobacter baumannii Clinical Strains Isolated in Warsaw, Poland

Acinetobacter baumannii is an important cause of nosocomial infections worldwide. The elucidation of the carbapenem resistance mechanisms of hospital strains is necessary for the effective treatment and prevention of resistance gene transmission. The main mechanism of carbapenem resistance in A. baumannii is carbapenemases, whose expressions are affected by the presence of insertion sequences (ISs) upstream of bla_CHDL genes. In this study, 61 imipenem-nonsusceptible A. baumannii isolates were characterized using phenotypic (drug-susceptibility profile using CarbaAcineto NP) and molecular methods. Pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) methods were utilized for the genotyping. The majority of isolates (59/61) carried one of the following acquired bla_CHDL genes: bla_OXA-24-like (39/59), ISAba1-bla_OXA-23-like (14/59) or ISAba3-bla_OXA-58-like (6/59). Whole genome sequence analysis of 15 selected isolates identified the following intrinsic bla_OXA-66 (OXA-51-like; n = 15) and acquired class D β-lactamases (CHDLs): ISAba1-bla_OXA-23 (OXA-23-like; n = 7), ISAba3-bla_OXA-58-ISAba3 (OXA-58-like; n = 2) and bla_OXA-72 (OXA-24-like; n = 6). The isolates were classified into 21 pulsotypes using PFGE, and the representative 15 isolates were found to belong to sequence type ST2 of the Pasteur MLST scheme from the global IC2 clone. The Oxford MLST scheme revealed the diversity among these studied isolates, and identified five sequence types (ST195, ST208, ST208/ST1806, ST348 and ST425). CHDL-type carbapenemases and insertion elements upstream of the bla_CHDL genes were found to be widespread among Polish A. baumannii clinical isolates, and this contributed to their carbapenem resistance.

Molecular Epidemiology and Mechanisms of Carbapenem-Resistant Acinetobacter baumannii Isolates from ICU and Respiratory Department Patients of a Chinese University Hospital

BACKGROUND

The objective of our study is to estimate the differences in molecular epidemiology and resistance mechanisms in carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from the ICU and respiratory department(RD) in Fourth Affiliated Hospital of Harbin Medical University.

METHODS

Carbapenemase genes associated with carbapenem resistance were studied by polymerase chain reaction(PCR). Genotyping was analyzed using multi-locus sequence typing (MLST) and pulsed field gel electrophoresis (PFGE).

RESULTS

Sixty non-duplicate CRAB isolates from the ICU and RD (n=30, respectively) were collected. All of CRAB strains were not resistant to colistin (0%). The CRAB strains from the ICU were significantly more resistant to tigecycline and cefoperazone/sulbactam compared with the RD (23.3% vs 0%, P=0.03; 53.3% % vs 23.3%, P=0.01, respectively). PCR detection of genes associated with CRAB revealed that the ratio in both the ICU and the RD of blaVIM-2, blaIMP-4, blaNDM-1, blaOXA-23, ampC, and mutation of CarO were present in 23.3% vs 0% (P=0.01), 40% vs 10% (P=0.02), 20% vs 0% (P=0.02), 80% vs 56.7%, 16.7% vs 13.3% and 86.7% vs 60% (P=0.04), respectively. Seven genotypes were detected by the PFGE in the RD and the ICU, respectively. Genotype I was significantly more frequent in the ICU compared with the RD (63.3% vs 36.6%, P=0.03). MLST showed that there were 10 ST genotypes in the RD and four in the ICU, but ST92 in both groups was 33.3% vs 63.3% (P=0.03), respectively.

CONCLUSION

There are differences in molecular epidemiology and resistance mechanisms in the CRAB isolates between the ICU and RD.

Acinetobacter baumannii as a community foodborne pathogen: Peptide mass fingerprinting analysis, genotypic of biofilm formation and phenotypic pattern of antimicrobial resistance

Acinetobacter baumannii (A. baumannii) is one of the most common Gram-negative pathogens that represent a major threat to human life. Because the prevalence of Multidrug-resistant biofilm-forming A. baumannii is increasing all over the world, this may lead to outbreaks of hospital infections. Nonetheless, the role of raw meat as a reservoir for A. baumannii remains unclear. Here our research was aimed to exhibit the frequency, precise identification, and genotyping of biofilm-related genes as well as antimicrobial resistance of A. baumannii isolates of raw meat specimens. Fifty-five A. baumannii strains were recovered from 220 specimens of different animal meat and then identified by Peptide Mass Fingerprinting Technique (PMFT). All identified isolates were genotyped by the qPCR method for the existence of biofilm-related genes (ompA, bap, blaPER-1, csuE, csgA, and fimH). In addition, the antimicrobial resistance against A. baumannii was detected by the Kirby-Bauer method. Based on our findings, the frequency rate of 55 A. baumannii isolates was 46.55%, 32.50%, 15.00%, and 9.68% of sheep, chicken, cow, and camel raw meat samples, respectively. The PMFT was able to identify all strains by 100%. the percentages of csuE, ompA, bla_PER-1, bap, and csgA genes in biofilm and non-biofilm producer A. baumannii were 72.73%, 60%, 58.2%, 52.74%, and 25.45%, respectively. In contrast, the fimH was not detected in all non-biofilm and biofilm producer strains. The ompA, bap, blaPER-1, csgA were detected only in biofilm-producing A. baumannii isolates. The maximum degree of resistance was observed against amoxicillin/clavulanic acid (89.10%), gentamicin (74.55%), tetracycline (72.73%), ampicillin (65.45%), and tobramycin (52.73%). In conclusion, our investigation demonstrated the high incidence of multi-drug resistant A. baumannii in raw meat samples, with a high existence of biofilm-related virulence genes of ompA, bap, blaPER-1, csgA. Therefore, it has become necessary to take the control measures to limit the development of A. baumannii.

An Evaluation of BfmR-Regulated Antimicrobial Resistance in the Extensively Drug Resistant (XDR) Acinetobacter baumannii Strain HUMC1

Acinetobacter baumannii is a problematic pathogen due to its common expression of extensive drug resistance (XDR) and ability to survive in the healthcare environment. These characteristics are mediated, in part, by the signal transduction system BfmR/BfmS. We previously demonstrated, in antimicrobial sensitive clinical isolates, that BfmR conferred increased resistance to meropenem and polymyxin E. In this study, potential mechanisms were informed, in part, by a prior transcriptome analysis of the antimicrobial sensitive isolate AB307-0294, which identified the porins OprB and aquaporin (Omp33-36, MapA) as plausible mediators for resistance to hydrophilic antimicrobials such as meropenem. Studies were then performed in the XDR isolate HUMC1, since delineating resistance mechanisms in this genomic background would be more translationally relevant. In HUMC1 BfmR likewise increased meropenem and polymyxin E resistance and upregulated gene expression of OprB and aquaporin. However, the comparison of HUMC1 with isogenic mutant constructs demonstrated that neither OprB nor aquaporin affected meropenem resistance; polymyxin E susceptibility was also unaffected. Next, we determined whether BfmR-mediated biofilm production affected either meropenem or polymyxin E susceptibilities. Interestingly, biofilm formation increased resistance to polymyxin E, but had little, if any effect on meropenem activity. Additionally, BfmR mediated meropenem resistance, and perhaps polymyxin E resistance, was due to BfmR regulated factors that do not affect biofilm formation. These findings increase our understanding of the mechanisms by which BfmR mediates intrinsic antimicrobial resistance in a clinically relevant XDR isolate and suggest that the efficacy of different classes of antimicrobials may vary under biofilm inducing conditions.

Antibiotic Susceptibility, Clonality, and Molecular Characterization of Carbapenem-Resistant Clinical Isolates of Acinetobacter baumannii from Washington DC

The occurrence of carbapenem-resistant (CR) strains of Acinetobacter baumannii is reported to contribute to the severity of several nosocomial infections, especially in critically ill patients in intensive care units. The present study aims to determine the antibiotic susceptibility, clonality, and genetic mechanism of carbapenem resistance in twenty-eight Acinetobacter baumannii isolates from four hospitals in Washington DC. The antibiotic susceptibility of the isolates was determined by VITEK 2 analyses, while PCR was used to examine the presence of antibiotic-resistant genes and mobile genetic elements. Trilocus multiplex-PCR was used along with pulsed-field gel electrophoresis (PFGE) for strain typing and for accessing clonal relationships among the isolates. Antimicrobial susceptibility testing indicated that 46% of the isolates were carbapenem-resistant and possessed MDR and XDR phenotypes. PFGE clustered the 28 isolates into seven clonal (C1–C7) complexes based on >75% similarity cut-off. Thirty-six percent of the isolates belonged to international clone II, while 29% were assigned to Group 4 by trilocus multiplex-PCR. Although the bla_OXA-51-like gene was found in all the isolates, only 36% were positive for the bla_OXA-23-like gene. PCR analysis also found a metallo-β-lactamase (MBL) gene (bla_VIM) in 71% of the isolates. Of the 13 CR isolates, 8 were PCR positive for both bla_VIM and bla_OXA-23-like genes, while 5 harbored only bla_VIM gene. This study revealed the emergence of VIM carbapenemase-producing A. baumannii isolates, which has not been previously reported in the United States.

Antibiotic Resistance Profiles, Molecular Mechanisms and Innovative Treatment Strategies of Acinetobacter baumannii

Antibiotic resistance is one of the biggest challenges for the clinical sector and industry, environment and societal development. One of the most important pathogens responsible for severe nosocomial infections is Acinetobacter baumannii, a Gram-negative bacterium from the Moraxellaceae family, due to its various resistance mechanisms, such as the β-lactamases production, efflux pumps, decreased membrane permeability and altered target site of the antibiotic. The enormous adaptive capacity of A. baumannii and the acquisition and transfer of antibiotic resistance determinants contribute to the ineffectiveness of most current therapeutic strategies, including last-line or combined antibiotic therapy. In this review, we will present an update of the antibiotic resistance profiles and underlying mechanisms in A. baumannii and the current progress in developing innovative strategies for combating multidrug-resistant A. baumannii (MDRAB) infections.

Molecular Detection of Carbapenemase-Encoding Genes in Multidrug-Resistant Acinetobacter baumannii Clinical Isolates in South Africa

Introduction

Carbapenem-resistant Acinetobacter baumannii has been responsible for an increasing number of hospital-acquired infections globally. The study investigated the prevalence of carbapenemase-encoding genes in clinical multidrug-resistant A. baumannii strains.

Materials and Methods

A total of 100 nonduplicate multidrug-resistant A. baumannii strains were cultured from clinical samples obtained from healthcare facilities in the O. R. Tambo district. The strains were confirmed by detecting the intrinsic bla_OXA-51-like gene. Antimicrobial susceptibility testing was performed by VITEK^® 2 and autoSCAN-4 systems. The MIC of imipenem and meropenem was rechecked by E-test. Colistin MIC was confirmed by the broth microdilution method. Real-time PCR was performed to investigate the presence of carbapenemase-encoding genes.

Results

Most strains showed high resistance rates (>80%) to the antibiotics tested. Resistance to amikacin, tetracycline, and tigecycline were 50%, 64%, and 48%, respectively. All strains were fully susceptible to colistin. The bla_OXA-51-like was detected in all strains whilst bla_OXA-23-like, bla_OXA-58-like, bla_OXA-24-like, bla_IMP-1, bla_VIM, and bla_NDM-1 were found in 70%, 8%, 5%, 4%, 3%, and 2% of strains, respectively. None of the tested strains harboured the genes bla_SIM and bla_AmpC. The coexistence of bla_OXA-23-like, and bla_IMP-1 or bla_OXA-58-like was detected in 1% and 2% strains, respectively. A distinct feature of our findings was the coharbouring of the genes bla_OXA-23-like, bla_OXA-58-like, and bla_IMP-1 in 2% strains, and this is the first report in the Eastern Cape Province, South Africa. The intI1 was carried in 80% of tested strains whilst ISAba1/bla_OXA-51-like and ISAba1/bla_OXA-23-like were detected in 15% and 40% of the strains, respectively. The detection of bla_OXA-23-like, ISAba1/bla_OXA-51-like, ISAba1/bla_OXA-23-like, and bla_OXA-23-like, bla_OXA-58-like, and bla_IMP-1 carbapenemases in strains had a significant effect on both imipenem and meropenem MICs.

Conclusions

Results showed a high level of oxacillinases producing A. baumannii circulating in our study setting, highlighting the need for local molecular surveillance to inform appropriate management and prevention strategies.

Co-existence of blaOXA-23 and blaVIM in carbapenem-resistant Acinetobacter baumannii isolates belonging to global complex 2 in a Chinese teaching hospital

Background

Carbapenem-resistant Acinetobacter baumannii (CRAB) have been a challenging concern of health-care associated infections. The aim of the current study was to investigate the molecular epidemiology and clonal dissemination of CRAB isolates in a Chinese teaching hospital.

Methods

Non-duplicate clinical A. baumannii isolates were collected from inpatients, and we measured the minimal inhibitory concentrations to determine antimicrobial susceptibility. Polymerase chain reaction (PCR) and sequencing were performed to detect carbapenem-resistance genes and occurrence of transposons among CRAB isolates. Moreover, the genetic diversity among isolates and clonal dissemination were determined by repetitive element PCR-mediated DNA fingerprinting (rep-PCR) and multilocus sequence typing (MLST).

Results

A total of 67 CRAB isolates displayed resistance to most of the antibiotics tested in this study, except tigecycline. We detected bla_OXA-23, bla_OXA-51, bla_OXA-58, and bla_VIM genes in 94.0%, 100.0%, 1.5%, and 80.6% of the CRAB isolates, respectively. Nevertheless, 74.6% of the CRAB isolates co-harbored the bla_OXA-23 and bla_VIM. Only one type of transposons was detected: Tn2008 (79.1%, 53/67). Although 12 distinctive types (A-L) were determined (primarily A type) ST195 was the most prevalent sequence type (ST). ST368, ST210, ST90, ST829, and ST136 were also detected, and all belonged to clonal complex 208 (CC208) and global complex 2 (GC2).

Conclusion

The bla_OXA-23 and bla_VIM genes contributed to the resistance among CRAB isolates collected in our study. Notably, most of the CRAB strains co-harbored bla_OXA-23 and bla_VIM genes, as well as Tn2008, which could contribute to clonal dissemination. The prevalence of such organisms may underlie hospital acquired infections.

Molecular characterization & epidemiology of carbapenem-resistant Acinetobacter baumannii collected across India

Background & objectives

Acinetobacter baumannii is an opportunistic pathogen responsible for causing nosocomial infections. A. baumannii develops resistance to various antimicrobial agents including carbapenems, thereby complicating the treatment. This study was performed to characterize the isolates for the presence of various β-lactamases encoding genes and to type the isolates to compare our clones with the existing international clones across five centres in India.

Methods

A total 75 non-repetitive clinical isolates of A. baumannii from five different centres were included in this study. All the isolates were confirmed as A. baumannii by bl a_OXA-51-likePCR. Multiplex PCR was performed to identify the presence of extended spectrum β-lactamases (ESBL) and carbapenemases. Multilocus sequence typing was performed to find the sequence type (ST) of the isolates. e-BURST analysis was done to assign each ST into respective clonal complex.

Results

bla_OXA-51-likewas present in all the 75 isolates. The predominant Class D carbapenemase was bla_OXA-23-likefollowed by Class B carbapenemase, bla_NDM-like. Class A carbapenemase was not observed. bla_PER-likewas the predominant extended spectrum β-lactamase. ST-848, ST-451 and ST-195 were the most common STs. Eight-novel STs were identified. e-BURST analysis showed that the 75 A. baumannii isolates were clustered into seven clonal complexes and four singletons, of which, clonal complex 208 was the largest.

Interpretation & conclusions

Most of the isolates were grouped under clonal complex 208 which belongs to the international clonal lineage 2. High occurrence of ST-848 carrying bla_OXA-23-likegene suggested that ST-848 could be an emerging lineage spreading carbapenem resistance in India.

Characteristics of Carbapenem-Resistant and Colistin-Resistant Escherichia coli Co-Producing NDM-1 and MCR-1 from Pig Farms in China

The emergence of carbapenem-resistant and colistin-resistant Enterobacteriaceae represents a great risk for public health. In this study, the phenotypical and genetic characteristics of eight carbapenem-resistant and colistin-resistant isolates from pig farms in China were determined by the broth microdilution method and whole genome sequencing. Antimicrobial susceptibility testing showed that the eight carbapenem-resistant and colistin-resistant strains were resistant to three aminoglycosides, twelve β-lactams, one of the phenicols, one of the tetracyclines, and one of the fluoroquinolones tested, simultaneously. The prediction of acquired resistant genes using the whole genome sequences revealed the co-existence of bla_NDM-1 and mcr-1 as well as the other genes that were responsible for the multidrug-resistant phenotypes. Bioinformatics analysis also showed that the carbapenem-resistant gene bla_NDM-1 was located on a putative IncFII-type plasmid, which also carried the other acquired resistant genes identified, including fosA3, blaTEM-1B and rmtB, while the colistin-resistant gene mcr-1 was carried by a putative IncX4-type plasmid. Finally, we found that these resistant genes/plasmids were conjugative, and they could be co-conjugated, conferring resistance to multiple types of antibiotics, including the carbapenems and colistin, to the recipient Escherichia coli strains.

Clonal relatedness and resistance characteristics of OXA-24 and -58 producing carbapenem-resistant Acinetobacter baumannii isolates in Tehran, Iran

AIMS

The present study was conducted to investigate the mechanism of carbapenem resistance and the molecular epidemiology of carbapenem-resistant Acinetobacter baumannii (CRAB) isolates collected from two nearby hospitals in Tehran, Iran.

METHODS AND RESULTS

A total of 180 CRAB isolates were studied. Antimicrobial susceptibility testing was performed using disk diffusion and Epsilometer tests. The detection of OXA-23, -24 and -58 was implemented for all isolates using polymerase chain reaction. Subsequently, isolates harbouring OXA-24 and -58 were investigated for the presence of resistance determinants of Ambler class A, metallo-β-lactamases (MBLs), and carbapenem-hydrolysing class D β-lactamases, ISAba1, and the genetic relatedness between them was analysed using pulsed-field gel electrophoresis (PFGE). All isolates were found to be resistant to imipenem with a MIC of ≥8 µg ml^-1 and were susceptible to colistin with a MIC of ≤1·5 µg ml^-1 . Sixty percent of the isolates had OXA-23. OXA-24 and -58 were detected in 31 of 180 CRAB isolates. These chosen isolates were devoid of MBLs and bla_SHV , bla_{C TX-M} , bla_VEB ESBL genes. The PER determinant was detected in 38% of isolates as the most common extended spectrum β-lactamases (ESBLs). Of these isolates, 51·6% had OXA-23, and ISAba1 was found to be upstream of OXA-23 and OXA-51 in 16 and 8 isolates, respectively. The band patterns produced by PFGE showed nine clonal pulsotypes distributed between the two hospitals.

CONCLUSION

The findings showed that the refractory CRAB isolates were transmitted intra- and inter-hospital, particularly in the ICU due to shortcomings in infection control surveillance.

SIGNIFICANCE AND IMPACT OF THE STUDY

Carbapenem resistance is a substantial threat in the treatment of infections caused by A. baumannii due to limitations in the therapeutic options.

Biofilm Formation in Acinetobacter Baumannii: Genotype-Phenotype Correlation

Strains of Acinetobacter baumannii are commensal and opportunistic pathogens that have emerged as problematic hospital pathogens due to its biofilm formation ability and multiple antibiotic resistances. The biofilm-associated pathogens usually exhibit dramatically decreased susceptibility to antibiotics. This study was aimed to investigate the correlation of biofilm-forming ability, antibiotic resistance and biofilm-related genes of 154 A. baumannii isolates which were collected from a teaching hospital in Taiwan. Biofilm-forming ability of the isolates was evaluated by crystal violet staining and observed by scanning electron microscopy. Antibiotic susceptibility was determined by disc diffusion method and minimum inhibitory concentration; the biofilm-related genes were screened by polymerase chain reaction. Results showed that among the 154 tested isolates, 15.6% of the clinical isolates were weak biofilm producers, while 32.5% and 45.4% of them possessed moderate and strong biofilm formation ability, respectively. The experimental results revealed that the multiple drug resistant isolates usually provided a higher biofilm formation. The prevalence of biofilm related genes including bap, bla_PER-1, csuE and ompA among the isolated strains was 79.2%, 38.3%, 91.6%, and 68.8%, respectively. The results indicated that the antibiotic resistance, the formation of biofilm and the related genes were significantly correlated. The results of this study can effectively help to understand the antibiotic resistant mechanism and provides the valuable information to the screening, identification, diagnosis, treatment and control of clinical antibiotic-resistant pathogens.

Circulation of imipenem-resistant Acinetobacter baumannii ST10, ST2 and ST3 in a university teaching hospital from Tehran, Iran

PURPOSE

Multi-drug resistant (MDR) Acinetobacter baumannii has introduced a worldwide health crisis. The purposes of this study were to characterize the clonal relatedness among MDR clinical strains and to introduce a new two-locus typing method confirmed by multi-locus sequence typing (MLST).

METHODOLOGY

In this study, we determined antimicrobial resistance, detected genes associated with carbapenem resistance and characterized clonal relatedness among 99 clinical isolates extracted from 82 hospitalized inpatients in a university hospital.

RESULTS

Of the 99 A. baumannii isolates, 92.9% (92/99) were resistant to imipenem and 97.9% (97/99) had an MDR profile. We found that the high prevalence of blaVIM [94.9% (94/99)] and blaOXA-23-like [93.93% (93/99)] is the main mechanism of carbapenem resistance. This study proposes a new two-locus typing (blaOXA-51-like and ampC) method for the rapid identification of clonal complexes (CCs). The results of this method and confirmation by MLST show that clinical isolates carry blaOXA-68 as well as ampC-10 or ampC-20 genes belonging to CC10 (ST10); blaOXA-66 and ampC-2 belonging to CC2 (ST2); and blaOXA-71 and ampC-3 belonging to CC3 (ST3). One isolate had blaOXA-90 with an undetermined allele number of ampC belonging to ST513.

CONCLUSION

The high prevalence of MDR strains and the circulation of four limited clones, including ST10 (45/99), ST2 (41/99), ST3 (12/99) and ST513 (1/99), in the clinical setting highlights the importance of a rigorous infection control programme. The two-locus typing method has more discrimination than the application of each method separately and it could be applied for the rapid determination of the CC without performing MLST.

Carbapenem resistance in Acinetobacter baumannii is associated with enhanced survival on hospital fabrics

The success of Acinetobacter baumannii as an emerging organism is probably linked to its high resistance to adverse environmental conditions. This study was conducted to analyze the association between some factors that may favor the dissemination of A. baumannii clinical isolates. A total of 47 clinical strains of A. baumannii were evaluated to carbapenem, the ability to produce biofilm, the susceptibility to some antiseptics, and the survival time on cotton fabrics. Most of the isolates were resistant to carbapenem (72.3%), produced biofilm (83%), and survived more than 7 (51%) days on fabrics. A significant association between decreased susceptibility to antiseptics containing chlorhexidine or triclosan and carbapenem resistance and survival on fabrics could be observed. The resistance to carbapenem was significantly associated with survival on fabric, but not with the ability to form biofilm. The survival of the isolates on fabric was not associated with the ability to produce biofilms. Characteristics, such as resistance to antibiotics, ability to form biofilm, and survival on dry surfaces, probably contribute to the proliferation of this organism when selected in the hospital environment and can partly explain its success as responsible for nosocomial infection.

AdeR-AdeS mutations & overexpression of the AdeABC efflux system in ciprofloxacin-resistant Acinetobacter baumannii clinical isolates

Background & objectives:

Overexpression of efflux pumps is a cause of acquired resistance to fluoroquinolones in Acinetobacter baumannii. The present study was done to investigate the presence and overexpression of AdeABC efflux system and to analyze the sequences of AdeR-AdeS regulatory system in ciprofloxacin-resistant A. baumannii isolates.

Methods:

Susceptibility of 50 clinical A. baumannii isolates to ciprofloxacin, imipenem, ceftazidime, cefepime and gentamicin antimicrobials was evaluated by agar dilution method. Isolates were screened for the evidence of active efflux pump. Isolates were also examined for adeR-adeS and adeB efflux genes by polymerase chain reaction (PCR). The adeR and adeS regulatory genes were sequenced to detect amino acid substitutions. Expression of adeB was evaluated by quantitative reverse-transcriptase PCR.

Results:

There were high rates of resistance to ciprofloxacin (88%), ceftazidime (88%), cefepime (74%) and imipenem (72%) and less resistance rate to gentamicin (64%). Phenotypic assay showed involvement of active efflux in decreased susceptibility to ciprofloxacin among 16 isolates. The 12.27-fold increase and 4.25-fold increase were found in adeB expression in ciprofloxacin-full-resistant and ciprofloxacin-intermediate-resistant isolates, respectively. Several effective mutations, including A91V, A136V, L192R, A94V, G103D and G186V, were detected in some domains of AdeR-AdeS regulators in the overexpressed ciprofloxacin-resistant isolates.

Interpretation & conclusions:

The results of this study indicated that overexpression of the AdeABC efflux pump was important to reduce susceptibility to ciprofloxacin and cefepime in A. baumannii that, in turn, could be triggered by alterations in the AdeR-AdeS two-component system. However, gene expression alone does not seem adequate to explain multidrug resistance phenomenon. These results could help plan improved active efflux pump inhibitors.

Prevalence and Mechanisms of Carbapenem Resistance Among Acinetobacter baumannii Clinical Isolates in Egypt

The increasing number of carbapenem-resistant Acinetobacter baumannii clinical isolates is a major concern, which restricts therapeutic options for treatment of serious infections caused by this emerging pathogen. The aim of this work is to assess the antimicrobial resistance profile and identify the molecular mechanisms involved in carbapenem resistance in A. baumannii isolated from different clinical sources in Mansoura University Hospitals, Egypt. Antimicrobial susceptibility testing has shown that resistance to carbapenem has dramatically increased (98%) with concomitant elevated levels of resistance to quinolones, trimethoprim/sulfamethoxazole, and aminoglycosides. Polymyxin B and colistin are considered the last resort. Random amplified polymorphic DNA (RAPD) typing method revealed great diversity among A. baumannii isolates. Coexistence of diverse intrinsic and acquired carbapenem-hydrolyzing β-lactamases has been detected in the tested isolates: Ambler class A: bla_KPC (56%) and bla_GES (48%), and Ambler class B: bla_NDM (30%), bla_SIM (28%), bla_VIM (20%), and bla_IMP (10%). Most isolates (94%) carried bla_OXA-23-like and bla_OXA-51-like simultaneously. bla_OXA-23-like was preceded by ISAba1 providing a potent promoter activity for its expression. Sequencing analysis revealed that ISAba1 has been also inserted in carbapenem resistance-associated outer membrane protein (OMP) (carO) gene in three isolates, two of which were clonal based on RAPD typing, leading to interruption of its expression as confirmed by SDS-PAGE analysis of OMP fractions. Carbapenem resistance genes are widely distributed among A. baumannii clinical isolates from different clinical sources. Therefore, enhanced infection control measures, effective barriers, and rational use of antimicrobials should be enforced in hospitals for minimizing the widespread resistance to carbapenems and all other antibiotics.

Insight into Acinetobacter baumannii: pathogenesis, global resistance, mechanisms of resistance, treatment options, and alternative modalities

Acinetobacter baumannii, once considered a low-category pathogen, has emerged as an obstinate infectious agent. The scientific community is paying more attention to this pathogen due to its stubbornness to last resort antimicrobials, including carbapenems, colistin, and tigecycline, its high prevalence of infections in the hospital setting, and significantly increased rate of community-acquired infections by this organism over the past decade. It has given the fear of pre-antibiotic era to the world. To further enhance our understanding about this pathogen, in this review, we discuss its taxonomy, pathogenesis, current treatment options, global resistance rates, mechanisms of its resistance against various groups of antimicrobials, and future therapeutics.

In vitro synergistic effect of amlodipine and imipenem on the expression of the AdeABC efflux pump in multidrug-resistant Acinetobacter baumannii

Introduction

Multidrug-resistant Acinetobacter baumannii (A. baumannii) has become one of the greatest threats worldwide to the therapeutic management of infections. Our previous research confirmed an in vitro synergistic effect of amlodipine and imipenem against A. baumannii, and this study is designed to understand its mechanism.

Methods

Sixty-four non-duplicate A. baumannii isolates were collected and tested for antimicrobial susceptibility by the disk diffusion method. PCR amplification and sequencing were used to identify the presence of the adeB, adeE, adeH, adeJ, abeM and abeS efflux pump genes. The minimal inhibitory concentrations of imipenem, imipenem+amlodipine and imipenem+carbonyl cyanide m–chlorophenyl-hydrazone against these isolates were also determined by the broth microdilution method before and after siRNA silencing of the expression of the adeABC efflux pump.

Results

In this study, the combination of amlodipine with imipenem showed synergistic antimicrobial activity against sixty-four A. baumannii isolates when compared with the activity of imipenem alone (p<0.025). In the multidrug-resistant group, AML was more effective than carbonyl cyanide m–chlorophenyl-hydrazone (p<0.001). The efflux pump genes adeB, adeE, adeH, adeJ, abeM and abeS were detected in 100% (4/64), 75% (48/64), 0% (0/64), 100% (64/64), 96.9% (62/64) and 96.9% (62/64) of the sixty-four A. baumannii isolates, respectively. The expression of the adeABC efflux pump genes in the multidrug-resistant group (5.05±19.25) is clearly higher than in the non-multidrug-resistant group (0.17±0.20), (p = 0.01). A gene silencing test verified that the mRNA expression levels of adeABC were decreased at 12 h and increased at 24 h, while the reversal of imipenem resistance by amlodipine disappeared at 12 h and reappeared at 24 h.

Conclusions

The combination of amlodipine with imipenem exhibits an in vitro synergistic antimicrobial effect on multidrug-resistant A. baumannii, which may be due to the inhibition of the AdeABC efflux pump.

Simultaneous emergence and rapid spread of three OXA-23 producing Acinetobacter baumannii ST208 strains in intensive care units confirmed by whole genome sequencing

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a common nosocomial bacterial pathogen with limited treatment options. CRAB outbreaks are disastrous for critically ill patients. This study investigated carbapenemase-produced A. baumannii outbreaks in a tertiary hospital. Although multiple outbreaks were suggested by pulse-field gel electrophoresis, the genetic lineages and evolution between these isolates were not clear. To investigate the genomic epidemiology of these outbreaks and to reveal possible transmission routes, whole genome sequences (WGS) were compared and analyzed. From the WGS data, thirty isolates had the same sequence type (ST208); acquired resistance genes and chromosome resistant genes were detected and were responsible for multidrug resistance. A phylogenetic tree of single-nucleotide polymorphisms (SNPs) compared to the earliest index isolate found that three outbreaks had emerged and disseminated simultaneously. Of these, <10 SNPs were detected within the cluster, whereas at least 600 SNPs were found between the clusters. The probable transmission routes of outbreaks were generated combined with the genetic distance of isolates and patient epidemiological data. In conclusion, WGS was a convenient and accurate monitoring method for genomic epidemiologic investigation of outbreaks, and the genomic surveillance of multidrug-resistant bacterial pathogens would be a powerful warning system for the surveillance and prevention of outbreaks.

Molecular Characterization and Antibiotic Susceptibility Pattern of Acinetobacter Baumannii Isolated in Intensive Care Unit Patients in Al-Hassa, Kingdom of Saudi Arabia

Background:

Acinetobacter baumannii, is an emerging nosocomial multidrug resistance pathogen with the rapid spread of clones being reported in health-care settings and hospitals worldwide. Carbapenem resistance in this bacterium has been attributed to D OXA β-lactamases with OXA-51-like β-lactamase, being present in all A. baumannii isolate. The present study looks into the antibiotics susceptibility and molecular characterization of clinical A. baumannii isolates from Intensive Care Unit (ICU) samples in Al-Hofuf, South-eastern region of Saudi Arabia.

Materials and Methods:

Eleven strains of ICU A. baumanni i isolates were used for the investigation. Bacteria isolation was by basic microbiological techniques. Organisms identification and antibiogram susceptibility testing was by the BioMerieux VITEK 2 compact automated system (BioMerieux, Marcy I'Etoile France), according to the manufacturers guidelines. Confirmation of A. baumannii was by the presence of the OX-51 gene, also, carbapenemase encoding resistant genesbla_OXA-23, bla_OXA-40, and bla_OXA-51, were analyzed using multiplex PCR. The Student's t test was used to analyze the obtained data for between group comparisons with statistically significance level set at P < 0.05.

Results:

Eight of the isolates were confirmed to be A. baumannii. Five of which were resistant to the carbapenems against which they had been tested. One isolate was resistant to tigecycline, whereas three tested intermediate to the drug. OXA-23 was detected in isolates 1, 4, 5, 6, and 7.

Conclusion:

It can, therefore, be concluded that the probable predominate carbapenems resistant genes in ICU isolates from the present investigation, are those associated with OXA-23.

Next-generation sequencing identification of pathogenic bacterial genes and their relationship with fecal indicator bacteria in different water sources in the Kathmandu Valley, Nepal

Bacteriological analysis of drinking water leads to detection of only conventional fecal indicator bacteria. This study aimed to explore and characterize bacterial diversity, to understand the extent of pathogenic bacterial contamination, and to examine the relationship between pathogenic bacteria and fecal indicator bacteria in different water sources in the Kathmandu Valley, Nepal. Sixteen water samples were collected from shallow dug wells (n=12), a deep tube well (n=1), a spring (n=1), and rivers (n=2) in September 2014 for 16S rRNA gene next-generation sequencing. A total of 525 genera were identified, of which 81 genera were classified as possible pathogenic bacteria. Acinetobacter, Arcobacter, and Clostridium were detected with a relatively higher abundance (>0.1% of total bacterial genes) in 16, 13, and 5 of the 16 samples, respectively, and the highest abundance ratio of Acinetobacter (85.14%) was obtained in the deep tube well sample. Furthermore, the bla_OXA23-like genes of Acinetobacter were detected using SYBR Green-based quantitative PCR in 13 (35%) of 37 water samples, including the 16 samples that were analyzed for next-generation sequencing, with concentrations ranging 5.3-7.5logcopies/100mL. There was no sufficient correlation found between fecal indicator bacteria, such as Escherichia coli and total coliforms, and potential pathogenic bacteria, as well as the bla_OXA23-like gene of Acinetobacter. These results suggest the limitation of using conventional fecal indicator bacteria in evaluating the pathogenic bacteria contamination of different water sources in the Kathmandu Valley.

Pneumonia caused by extensive drug-resistant Acinetobacter baumannii among hospitalized patients: genetic relationships, risk factors and mortality

BACKGROUND

The clonal spread of multiple drug-resistant Acinetobacter baumannii is an emerging problem in China. We analysed the molecular epidemiology of Acinetobacter baumanni isolates at three teaching hospitals and investigated the risk factors, clinical features, and outcomes of hospital-acquired pneumonia caused by extensive drug-resistant Acinetobacter baumannii (XDRAB) infection in Guangzhou, China.

METHODS

Fifty-two A. baumannii isolates were collected. Multilocus sequence typing (MLST) was used to assess the genetic relationships among the isolates. The bla _OXA-51-like gene was amplified using polymerase chain reaction (PCR) and sequencing. The resistance phenotypes were determined using the disc diffusion method. A retrospective case-control study was performed to determine factors associated with XDRAB pneumonia.

RESULTS

Most of the 52 A. baumannii isolates (N = 37, 71.2%) were collected from intensive care units (ICUs). The respiratory system was the most common bodily site from which A. baumannii was recovered (N = 45, 86.5%). Disc diffusion classified the isolates into 17 multidrug-resistant (MDR) and 35 extensively drug-resistant (XDR) strains. MLST grouped the A. baumannii isolates into 5 existing sequence types (STs) and 7 new STs. ST195 and ST208 accounted for 69.2% (36/52) of the isolates. The clonal relationship analysis showed that ST195 and ST208 belonged to clonal complex (CC) 92. According to the sequence-based typing (SBT) of the bla _OXA-51-like gene, 51 A. baumannii isolates carried OXA-66 and the rest carried OXA-199. There were no significant differences with respect to the resistance phenotype between the CC92 and non-CC92 strains (P = 0.767). The multivariate analysis showed that the APACHE II score, chronic obstructive pulmonary disease (COPD) and cardiac disease were independent risk factors for XDRAB pneumonia (P < 0.05). The mortality rate of XDRAB pneumonia was high (up to 42.8%), but pneumonia caused by XDRAB was not associated with in-hospital mortality (P = 0.582).

CONCLUSIONS

ST195 may be the most common ST in Guangzhou, China, and may serve as a severe epidemic marker. SBT of bla _OXA-51-like gene variants may not result in sufficient dissimilarities to type isolates in a small-scale, geographically restricted study of a single region. XDRAB pneumonia was strongly related to systemic illnesses and the APACHE II score but was not associated with in-hospital mortality.

Correlation between ability of biofilm formation with their responsible genes and MDR patterns in clinical and environmental Acinetobacter baumannii isolates

Acinetobacter baumannii potential to form biofilm and exhibit multiple antibiotic resistances may be responsible in its survival in hospital environment. Accordingly, our study was aimed to determine the correlation between ability of biofilm formation and the frequency of biofilm related genes with antibiotic resistance phenotypes, and also the categorization of their patterns in clinical and environmental isolates. A total of 75 clinical and 32 environmental strains of the A. baumannii were collected and identified via API 20NE. Antibiotic susceptibility was evaluated by disk diffusion and microdilution broth methods. Biofilm formation assay was performed by microtiter plate method. OXA types and biofilm related genes including Bla_OXA-51, Bla_OXA-23, Bla_OXA-24, Bla_OXA-58, bap, bla_PER-1, and ompA were amplified by PCR. The rate of MDR A. baumannii in clinical isolates (100%) was higher than environmental (81.2%) isolates (p < 0.05). Among 10 antibiotypes, the predominant resistance pattern in clinical and environmental isolates was antibiotypes I (85.3 and 78.1%, respectively). Analysis of the frequency of bla_OXA-23 gene revealed a statistically significant difference between clinical (85.3%) and environmental (68.7%) isolates (p < 0.05). The prevalence of strong biofilm producers in clinical and environmental isolates were 31.2%-58.7%, respectively. In the clinical and environmental isolates, the frequencies of ompA, bla_RER-1 and bap genes were 100%, 53.3%, 82.7% and 100%, 37.5%, 84.4% respectively. Statistical analysis revealed a significant correlation between the frequency of MDR isolates and biofilm formation ability (p = 0.008). The high frequency of antibiotype I would be indicated that an outbreak has been happened earlier and an endemic strain is currently being settled in the hospital environment. It would be suggested that if there was no difference in the frequency of pattern I and biofilm formation ability between clinical and environmental isolates, it is a critical point representing the higher risk of bacterial transmission from environment to the patients. The resulting data would be assisted in the improvement of disinfection strategies to better control of nosocomial infections. One dominant resistance pattern has shown among clinical and environmental isolates. The frequency of blaOXA-23 had significant difference between clinical and environmental isolates. The presence of bap gene in the A. baumannii isolates was associated with biofilm formation. There was a significant correlation between multiple drug resistance and biofilm formation. The clinical isolates had a higher ability to form strong biofilms compared to the environmental samples.

Clinical and molecular epidemiology of Acinetobacter baumannii bloodstream infections in an endemic setting

AIM

The transmission dynamics of Acinetobacter baumannii in endemic settings, and the relation between microbial properties and patients' clinical outcomes, are yet obscure and hampered by insufficient metadata.

METHODS & RESULTS

Of 20 consecutive patients with A. baumannii bloodstream infection that were thoroughly analyzed at a single center, at least one transmission opportunity was evident for 85% of patients. This implies that patient-to-patient transmission is the major mode of A. baumannii acquisitions in health facilities. Moreover, all patients who died immediately (<24 h of admission) were infected with a single clone (ST457; relative risk = 1.6; p = 0.05).

CONCLUSION

This preliminary analysis should prompt further investigation by mapping genomic virulence determinants among A. baumannii ST457 lineage compared with other strains.

Multilocus Sequence Typing Analysis of Carbapenem-Resistant Acinetobacter baumannii in a Chinese Burns Institute

Acinetobacter baumannii is a leading pathogen responsible for nosocomial infections. The emergence of carbapenem-resistant A. baumannii (CRAB) has left few effective antibiotics for clinicians to use. To investigate the temporal evolutionary relationships among CRAB strains, we collected 248 CRAB isolates from a Chinese burns institute over 3 years. The prevalence of the OXA-23 gene was detected by polymerase chain reaction. Multilocus sequence typing was used to type the CRAB strains and eBURST was used to analyze their evolutionary relationships. Wound surfaces (41%), sputa (24%), catheters (15%), and bloods (14%) were the four dominant isolation sources. Except for minocycline (33.5%) and sulbactam/cefoperazone (74.6%), these CRAB strains showed high resistance rates (>90%) to 16 tested antibiotics. The 248 isolates fall into 26 sequence types (STs), including nine known STs and 17 unknown STs. The majority (230/248) of these isolates belong to clonal complex 92 (CC92), including eight isolates belonging to seven unreported STs. A new CC containing 11 isolates grouped into four new STs was identified. The OXA-23 gene was detected at high prevalence among the CRAB isolates and the prevalence rate among the various STs differed. The majority of the isolates displayed a close evolutionary relationship, suggesting that serious nosocomial spreading and nosocomial infections of CRAB have occurred in the burn unit. In conclusion, the main CC for CRAB in this Chinese burn unit remained unchanged during the 3-year study period, and a new CC was identified. CC92 was the dominant complex, and more attention should be directed toward monitoring the new CC we have identified herein.

Wide spread of OXA-23-producing carbapenem-resistant Acinetobacter baumannii belonging to clonal complex II in different hospitals in Lebanon

OBJECTIVES

To investigate the molecular epidemiology of Acinetobacter baumannii strains isolated from different hospitals in Lebanon.

METHODS

A total of 119 non-duplicate Acinetobacter strains were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and partial rpoB gene sequencing. Antibiotic susceptibility testing was performed by disc diffusion method and all identified carbapenem-resistant isolates were investigated by PCR assays for the presence of the carbapenemase-encoding genes. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were used for molecular typing.

RESULTS

Of the 119 A. baumannii isolates, 76.5% were resistant to carbapenems. The most common carbapenemase was the OXA-23-type, found in 82 isolates. The study of population structure using MLST revealed the presence of 30 sequence types (STs) including 18 new ones, with ST2 being the most commonly detected, accounting for 61% of the isolates typed. PFGE performed on all strains of ST2 identified a major cluster of 53 isolates, in addition to three other minor clusters and ten unique profiles.

CONCLUSIONS

This study highlights the wide dissemination of highly related OXA-23-producing carbapenem-resistant A. baumannii belonging to the international clone II in Lebanon. Thus, appropriate infection control measures are recommended in order to control the geographical spread of this clone in this country.

Epidemiological characterization of Acinetobacter baumannii bloodstream isolates from a Chinese Burn Institute: A three-year study

Acinetobacter baumannii infection is a serious threat to burn patients. Bacteremia due to A. baumannii is becoming the most common cause of mortality following burn. However, the epidemiology of A. baumannii causing burn-related bloodstream infections has rarely been reported. We retrospectively collected 81 A. baumannii isolates from the bloodstream of burn patients over a three-year period. Antibiotic susceptibility tests, the prevalence of antibiotic-resistant genes and sequence typing (ST) were conducted to characterize these strains. Most of the isolates showed an extensive drug-resistant phenotype. The resistance frequencies to imipenem and meropenem were 94% and 91%, respectively. The blaOXA-23-like gene, AmpC, IS-AmpC, PER and SIM are the five most prevalent resistant genes, and their prevalence rates are 93% (75/81), 86% (70/81), 73% (59/81), 73% (59/81) and 52% (42/81), respectively. The 81 isolates were grouped into 10 known and 18 unknown ST types, with ST368 (38%) being the most prevalent. Except for ST457 and four new types (STn2, STn6, STn11 and STn14), the remaining 23 ST types belonged to one clonal complex 92, which is most common among clinical isolate in China. The above results indicated that ST368 isolates possessing both the blaOXA-23-like gene and ampC gene were the main culprits of the increasing nosocomial A. baumannii infection in this study. More attention should be paid to monitoring the molecular epidemiology of A. baumannii isolates from burn patients to prevent further distribution. Such information may help clinicians with therapeutic decisions and infection control in the Burns Institute.