Molecular Epidemiology of Emerging blaOXA-23-Like- and blaOXA-24-Like-Carrying Acinetobacter baumannii in Taiwan

Whole genome sequencing insight into carbapenem-resistant and multidrug-resistant Acinetobacter baumannii harboring chromosome-borne blaOXA-23

Carbapenem-resistant Acinetobacter baumannii (CRAB) poses a significant threat to hospitalized patients as effective therapeutic options are scarce. Based on the genomic characteristics of the CRAB strain AB2877 harboring chromosome-borne blaOXA-23, which was isolated from the bronchoalveolar lavage fluid (BALF) of a patient in a respiratory intensive care unit (RICU), we systematically analyzed antibiotic resistance genes (ARGs) and the genetic context associated with ARGs carried by CRAB strains harboring chromosome-borne blaOXA-23 worldwide. Besides blaOXA-23, other ARGs were detected on the chromosome of the CRAB strain AB2877 belonging to ST208/1806 (Oxford MLST scheme). Several key genetic contexts associated with the ARGs were identified on the chromosome of the CRAB strain AB2877, including (1) the MDR region associated with blaOXA-23, tet(B)-tetR(B), aph(3'')-Ib, and aph(6)-Id (2); the resistance island AbGRI3 harboring armA and mph(E)-msr(E) (3); the Tn3-like composite transposon containing blaTEM-1D and aph(3')-Ia; and (4) the structure "ISAba1-blaADC-25." The first two genetic contexts were most common in ST195/1816, followed by ST208/1806. The last two genetic contexts were found most frequently in ST208/1806, followed by ST195/1816.IMPORTANCEThe blaOXA-23 gene can be carried by plasmid or chromosome, facilitating horizontal genetic transfer and increasing carbapenem resistance in healthcare settings. In this study, we focused on the genomic characteristics of CRAB strains harboring the chromosome-borne blaOXA-23 gene, and the important genetic contexts associated with blaOXA-23 and other ARGs were identified, and their prevalent clones worldwide were determined. Notably, although the predominant clonal CRAB lineages worldwide containing the MDR region associated with blaOXA-23, tet(B)-tetR(B), aph(3'')-Ib, and aph (6)-Id was ST195/1816, followed by ST208/1806, the CRAB strain AB2877 in our study belonged to ST208/1806. Our findings contribute to the knowledge regarding the dissemination of CRAB strains and the control of nosocomial infection.

Whole genome sequencing and genomic characteristics analysis of carbapenem-resistant Acinetobacter baumannii clinical isolates in two hospitals in China

Nosocomial outbreaks caused by carbapenem-resistant Acinetobacter baumannii (CRAB) strains are rapidly emerging worldwide and are cause for concern. Herein, we aimed to describe the genomic characteristics of CRAB strains isolated from two hospitals in China in 2023. The A. baumannii isolates were mainly collected from the ICU and isolated from the sputum (71.43%, 15/21), followed by urine (14.29%, 3/21). Twenty-one A. baumannii strains possessed a multidrug-resistant (MDR) profile, and whole-genome sequencing showed that they all carried blaOXA-23. Based on the Pasteur multilocus sequence typing (MLST) scheme, all strains were typed into a sequence type 2 (ST2). Based on the Oxford MLST scheme, six strains belonged to ST540, three of which were ST208, and four strains were assigned to ST784. Kaptive showed most of the strains (38.10%, 8/21) contained KL93. As for the lipoolygosaccharide (OC locus) type, OCL1c and OCL1d were identified, accounting for 33.33% (7/21) and 66.67% (14/21), respectively. Based on the BacWGSTdb server, we found that the strains belonging to ST540 and ST784 were all collected from China. However, the ST938 strains were isolated from Malaysia and Thailand. Comparative genomics analysis showed that the AB10 strain had a closed relationship with SXAB10-SXAB13 strains, suggesting the transmission happened in these two hospitals and other hospital in China. In addition, the 4300STDY7045869 strain, which was collected from Thailand, possessed near genetic relationship with our isolates in this study, suggesting the possible spread among various countries. Additionally, 3-237 single nucleotide polymorphisms were observed among these strains. In conclusion, this study conducted a genome-based study for A. baumannii strains collected from two hospitals in China and revealed their epidemiological and molecular features. Clone spreading occurred in these two hospitals. Hence, there is an urgent need for increased surveillance in hospitals and other clinical settings to prevent and control CRAB spreading.

Deciphering the impact of Acinetobacter baumannii on human health, and exploration of natural compounds as efflux pump inhibitors to treat multidrug resistance

Acinetobacter baumannii is an ESKAPE pathogen and threatens human health by generating infections with high fatality rates. A. baumannii leads to a spectrum of infections such as skin and wound infections, endocarditis, meningitis pneumonia, septicaemia and urinary tract infections. Recently, strains of A. baumannii have emerged as multidrug-resistant (MDR), meaning they are resistant to at least three different classes of antibiotics. MDR development is primarily intensified by widespread antibiotic misuse and inadequate stewardship. The World Health Organization (WHO) declared A. baumannii a precarious MDR species. A. baumannii maintains the MDR phenotype via a diverse array of antimicrobial metabolite-hydrolysing enzymes, efflux of antibiotics, impermeability and antibiotic target modification, thereby complicating treatment. Hence, a deeper understanding of the resistance mechanisms employed by MDR A. baumannii can give possible approaches to treat antimicrobial resistance. Resistance-nodulation-cell division (RND) efflux pumps have been identified as the key contributors to MDR determinants, owing to their capacity to force a broad spectrum of chemical substances out of the bacterial cell. Though synthetic inhibitors have been reported previously, their efficacy and safety are of debate. As resistance-modifying agents, phytochemicals are ideal choices. These natural compounds could eliminate the bacteria or interact with pathogenicity events and reduce the bacteria's ability to evolve resistance. This review aims to highlight the mechanism behind the multidrug resistance in A. baumannii and elucidate the utility of natural compounds as efflux pump inhibitors to deal with the infections caused by A. baumannii.

The using of the polymerase chain reaction for the detection of resistance genes in gram-negative bacteria in routine practice in a pediatric hospital

Objective - assessment of RT-PCR for the detection of carbapenem-resistance genes in gram-negative bacteria. A total, 499 strains of gram-negative microorganisms isolated in two pediatric hospitals in 2019-2020 were studied. Species identification was performed using MALDI-ToF mass-spectrometry (Bruker Daltonics, Germany). Meropenem and imipenem minimal inhibitory concentration (MIC) was determined by E-test method (BioMerieux, France). The presence of acquired carbapenemase genes of IMP, NDM, VIM, KPC, OXA-48, OXA-23, OXA-40, OXA-58-groups was determined by RT-PCR. Klebsiella pneumoniae (34%), Escherichia coli (4%), Serratia marcescens (6%) and other members of Enterobacterales (6%), also gram-negative non-glucose-fermenting bacteria Acinetobacter baumannii (14%), Pseudomonas aeruginosa (36%) were found among selected strains. Carbapenemase production was found in 385 isolates (77%). The main mechanism determining carbapenem resistance in P. aeruginosa was the production of blaVIM (100%). A. baumanii strains harbored OXA-23 (55%) and OXA-40 (45%) carbapenemases. The major determinant of carbapenem resistance in K. pneumoniae isolates was OXA-48 carbapenemase, detected in 63% strains, 13% of the strains possessed blaNDM-group, 16% isolates had a combination of blaNDM-group and blaOXA-48-like. Carbapenemase of KPC-group was found in 8% K. pneumoniae strains. OXA-48 carbapenemase prevailed (95%) among S. marcescens strains. Most of E. coli isolates harbored metallo-beta-lactamase NDM (89%). Other members of Enterobacterales most often had OXA-48 carbapenemase (57%), 39% of the isolates carried blaNDM-group. In one strain, a combination of blaNDM-group and blaOXA-48-like was discovered. RT-PCR is a fast and reliable method for the detection of acquired carbapenemases and can be recommended for routine use in bacteriological laboratories.

Whole-genome analysis of carbapenem-resistant Acinetobacter baumannii from clinical isolates in Southern Thailand

The worldwide spread of carbapenem-resistant Acinetobacter baumannii (CRAB) has become a healthcare challenge for some decades. To understand its molecular epidemiology in Southern Thailand, we conducted whole-genome sequencing (WGS) of 221 CRAB clinical isolates. A comprehensive bioinformatics analysis was performed using several tools to assemble, annotate, and identify sequence types (STs), antimicrobial resistance (AMR) genes, mobile genetic elements (MGEs), and virulence genes. ST2 was the most prevalent ST in the CRAB isolates. For the detection of AMR genes, almost all CRAB isolates carried the bla_OXA-23 gene, while certain isolates harbored the bla_NDM-1 or bla_IMP-14 genes. Also, various AMR genes were observed in these CRAB isolates, particularly aminoglycoside resistance genes (e.g., armA, aph(6)-Id, and aph(3″)-Ib), fosfomycin resistance gene (abaF), and tetracycline resistance genes (tet(B) and tet(39)). For plasmid replicon typing, RepAci1 and RepAci7 were the predominant replicons found in the CRAB isolates. Many genes encoding for virulence factors such as the ompA, adeF, pgaA, lpxA, and bfmR genes were also identified in all CRAB isolates. In conclusion, most CRAB isolates contained a mixture of AMR genes, MGEs, and virulence genes. This study provides significant information about the genetic determinants of CRAB clinical isolates that could assist the development of strategies for improved control and treatment of these infections.

Molecular epidemiology of carbapenem-resistant Acinetobacter baumannii isolated from three major hospitals in Jordan

BACKGROUND

In the last decade, incidences of carbapenem-resistant Acinetobacter baumannii have been increasingly reported worldwide. Consequently, A. baumannii was included in the World Health Organization's new list of critical pathogens, for which new drugs are desperately needed. The objective of this research was to study the molecular epidemiology and antimicrobial susceptibility of clinical carbapenem-resistant A. baumannii isolated from Jordanian hospitals.

METHODS

A total of 78 A. baumannii and 8 Acinetobacter spp. isolates were collected from three major hospitals in Jordan during 2018. Disc diffusion and microdilution methods were used to test their susceptibility against 19 antimicrobial agents. Multilocus sequence typing (MLST) was performed using the Pasteur scheme, followed by eBURST analysis for all isolates. PCR was used to detect β-lactam resistance genes, bla_OXA-23-like , bla_OXA-51-like , and bla_NDM-1 .

RESULTS

Of the 86 tested isolates, 78 (90.6%) exhibited resistance to carbapenems, whereas no resistance was recorded to tigecycline or polymyxins. Based on the resistance profiles, 10.4% and 84.8% of isolates were classified into multidrug resistant (MDR) or extensively drug resistant (XDR), respectively. The most prevalent carbapenems resistance genes amongst isolates were bla_OXA-51-Like (89.5%), followed by bla_OXA-23-Like (88.3%) and bla_NDM-1 (10.4%). MLST revealed the presence of 19 sequence types (STs), belonging to eight different international complexes. The most commonly detected clonal complex (CC) was CC2, representing 64% of all typed isolates.

CONCLUSIONS

This is the first study to report the clonal diversity of A. baumannii isolates in Jordan. A high incidence of carbapenem resistance was detected in the isolates investigated. In addition, our findings provided evidence for the widespread of bla_OXA-23-like harbouring carbapenem-resistant A. baumannii and belonging to CC2. The number of XDR isolates identified in this study is alarming. Thus, periodic surveillance and molecular epidemiological studies of resistance factors are important to improve treatment outcomes and prevent the spread of A. baumannii infections.

Exploring the association between capsular types, sequence types, and carbapenemase genes in Acinetobacter baumannii

Acinetobacter baumannii is the main cause of nosocomial infections, and the treatment of such infections has become more difficult due to the emergence of carbapenem resistance. This study focused on major carbapenemase genes and explored the association between carbapenemase genes, sequence types (ST types), and capsular types (K types). A total of 98 carbapenem-resistant A. baumannii (CRAB) strains were collected from two hospitals, the Chang Gung Memorial Hospital-Lin Kou branch (LCGMH) in northern Taiwan and the CGMH-Kaohsiung branch (KCGMH) in southern Taiwan, from 2015-2017. Major carbapenemase genes of class A, B, and D β-lactamases were detected by polymerase chain reaction. All strains except 1 were positive for bla_OXA-51-like, 76 strains (77.6%) carried bla_OXA-23-like, and 25 strains (25.5%) carried bla_OXA-24-like. The regional distribution showed that bla_OXA-23-like was more predominant than bla_OXA-24-like in both hospitals (85.3% and 60% in LCGMH and KCGMH, respectively); however, bla_OXA-24-like displayed a much higher percentage in KCGMH (46.7%) than in LCGMH (16.2%). Oxford multilocus sequence typing and global optimal eBURST analysis were conducted for 59 strains. We revealed the association between bla_OXA gene patterns, ST types, and K types and demonstrated that four major K types, KL2, KL10, KL22, and KL52, which were associated with specific ST types, were mainly clustered into clonal complexes CC208 and CC549 (a unique clonal complex found in Taiwan). These findings provide important information for monitoring the epidemiology and dissemination of this pathogen.

Phenotypic and genotypic characterisation of cephalosporin-, carbapenem- and colistin-resistant Gram-negative bacterial pathogens in Lebanon, Jordan and Iraq

Antimicrobial resistance (AMR) is a worldwide health concern that continues to escalate. A PubMed literature search identified articles from January 2015-August 2020 reviewing cephalosporin-, carbapenem- and colistin-resistant Gram-negative bacteria (GNB) in Lebanon, Jordan and Iraq, specifically focused on three main pathogens, namely Acinetobacter spp., Enterobacteriaceae (i.e. Escherichia coli and Klebsiella spp.) and Pseudomonas aeruginosa. Sixty-seven relevant articles published within the past 5 years highlighting trends in AMR in Lebanon, Jordan and Iraq were included. Increased resistance to carbapenems in Acinetobacter spp. isolates was observed in Lebanon, Jordan and Iraq; colistin resistance remained relatively low. Studies on Enterobacteriaceae isolates were more varied, with high rates of carbapenem and cephalosporin resistance and lower levels of colistin resistance in Lebanon. Studies from Iraq found high cephalosporin and colistin resistance along with increased susceptibility to carbapenems. In Jordan, most studies recorded high resistance to cephalosporins along with high susceptibility to carbapenems and colistin. Studies on P. aeruginosa isolates were limited: most isolates in Lebanon were carbapenem-resistant and colistin-susceptible; studies in Iraq showed varying levels of resistance to carbapenems and cephalosporins with high susceptibility to colistin; and studies in Jordan found varying levels of susceptibility to carbapenems, cephalosporins and colistin. The most commonly observed resistance mechanisms in GNB were genetic modifications causing increased expression of antimicrobial-inactivating enzymes and decreased permeability. Overall, this review highlights the concerning rise in AMR and the need for improved understanding of the resistance mechanisms to better inform healthcare providers when recommending treatment for patients in this region.

Clinical and molecular characterization of Acinetobacter seifertii in Taiwan

OBJECTIVES

Acinetobacter seifertii, a new member of the Acinetobacter baumannii group, has emerged as a cause of severe infections in humans. We investigated the clinical and molecular characteristics of A. seifertii.

PATIENTS AND METHODS

This retrospective study enrolled 80 adults with A. seifertii bloodstream infection (BSI) at four medical centres over an 8 year period. Species identification was confirmed by MALDI-TOF MS, rpoB sequencing and WGS. Molecular typing was performed by MLST. Clinical information, antimicrobial susceptibility and the mechanisms of carbapenem and colistin resistance were analysed. Transmissibility of the carbapenem-resistance determinants was examined by conjugation experiments.

RESULTS

The main source of A. seifertii BSI was the respiratory tract (46.3%). The 28 day and in-hospital mortality rates of A. seifertii BSI were 18.8% and 30.0%, respectively. High APACHE II scores and immunosuppressant therapy were independent risk factors for 28 day mortality. The most common MLST type was ST553 (58.8%). Most A. seifertii isolates were susceptible to levofloxacin (86.2%), and only 37.5% were susceptible to colistin. Carbapenem resistance was observed in 16.3% of isolates, mostly caused by the plasmid-borne ISAba1-blaOXA-51-like genetic structure. A. seifertii could transfer various carbapenem-resistance determinants to A. baumannii, Acinetobacter nosocomialis and other A. seifertii isolates. Variations of pmrCAB and lpxCAD genes were not associated with colistin resistance of A. seifertii.

CONCLUSIONS

Levofloxacin and carbapenems, but not colistin, have the potential to be the drug of choice for A. seifertii infections. A. seifertii can transfer carbapenem-resistance determinants to other species of the A. baumannii group and warrants close monitoring.

In vitro and in vivo activities of imipenem combined with BLI-489 against class D β-lactamase-producing Acinetobacter baumannii

BACKGROUND

According to our preliminary study, BLI-489 has the potential to inhibit the hydrolysing activity of OXA-51-like β-lactamase produced by carbapenem-resistant Acinetobacter baumannii (CRAb).

OBJECTIVES

In the present study, the in vitro and in vivo activities of imipenem combined with BLI-489 against CRAb producing carbapenem-hydrolysing class D β-lactamases (CHDLs), namely OXA-23, OXA-24, OXA-51 and OXA-58, were determined.

METHODS

A chequerboard analysis of imipenem and BLI-489 was performed using 57 and 7 clinical CRAb isolates producing different CHDLs and MBLs, respectively. Four representative strains harbouring different CHDL genes were subjected to a time-kill assay to evaluate the synergistic effects. An in silico docking analysis was conducted to simulate the interactions between BLI-489 and the different families of CHDLs. The in vivo activities of this combination were assessed using a Caenorhabditis elegans survival assay and a mouse pneumonia model.

RESULTS

Chequerboard analysis showed that imipenem and BLI-489 had a synergistic effect on 14.3, 92.9, 100, 16.7 and 100% of MBL-, OXA-23-, OXA-24-like-, OXA-51-like- and OXA-58-producing CRAb isolates, respectively. In the time-kill assay, imipenem and BLI-489 showed synergy against OXA-24-like-, OXA-51-like- and OXA-58-, but not OXA-23-producing CRAb isolates after 24 h. The in silico docking analysis showed that BLI-489 could bind to the active sites of OXA-24 and OXA-58 to confer strong inhibition activity. The combination of imipenem and BLI-489 exhibited synergistic effects for the rescue of CRAb-infected C. elegans and mice.

CONCLUSIONS

Imipenem combined with BLI-489 has synergistic effects against CHDL-producing CRAb isolates.

Molecular Epidemiology of Extensively-Drug Resistant Acinetobacter baumannii Sequence Type 2 Co-Harboring bla NDM and bla OXA From Clinical Origin

Background

The therapeutic management of carbapenem-resistant Acinetobacter baumannii (CR-AB) represents a serious challenge to the public health sector because these pathogens are resistant to a wide range of antibiotics, resulting in limited treatment options. The present study was planned to investigate the clonal spread of CR-AB in a clinical setting.

Methodology

A total of 174 A. baumannii clinical isolates were collected from a tertiary care hospitals in Lahore, Pakistan. The isolates were confirmed by VITEK 2 compact system and molecular identification of recA and bla_OXA-51. Antimicrobial profile and the screening of carbapenem-resistant genes were carried out using VITEK 2 system and PCR, respectively. The molecular typing of the isolates was performed according to the Pasteur scheme.

Results

Of the 174 A. baumannii isolates collected, the majority were isolated from sputum samples (46.5%) and in the intensive care unit (ICU, 75%). Among these, 113/174 (64.9%) were identified as CR-AB, and 49.5% and 24.7% harbored bla_OXA-23 and bla_NDM-1, respectively. A total of 11 (9.7%) isolates co-harbored bla_OXA-51, bla_NDM-1, and bla_OXA-23. Interestingly, 46.9% of the CR-AB belonged to sequence type 2 (ST2; CC1), whereas 15.9% belonged to ST1 (CC1). All of the CR-AB isolates showed extensive resistance to clinically relevant antibiotics, except colistin.

Conclusion

The study concluded CR-AB ST2 clone harboring bla_OXA-23 and bla_NDM-1 are widely distributed in Pakistan’s clinical settings, which could result in increased mortality. Strict compliance with the National Action Plan on Antimicrobial Resistance is necessary to reduce the impacts of these strains.

Prevalence of OXA-Type β-Lactamase Genes among Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates in Thailand

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a critical health concern for the treatment of infectious diseases. The aim of this study was to investigate the molecular epidemiology of CRAB emphasizing the presence of oxacillinase (OXA)-type β-lactamase-encoding genes, one of the most important carbapenem resistance mechanisms. In this study, a total of 183 non-repetitive CRAB isolates collected from 11 tertiary care hospitals across Thailand were investigated. As a result, the blaoxa-51-like gene, an intrinsic enzyme marker, was detected in all clinical isolates. The blaoxa-23-like gene was presented in the majority of isolates (68.31%). In contrast, the prevalence rates of blaoxa-40/24-like and blaoxa-58-like gene occurrences in CRAB isolates were only 4.92% and 1.09%, respectively. All isolates were resistant to carbapenems, with 100% resistance to imipenem, followed by meropenem (98.91%) and doripenem (94.54%). Most isolates showed high resistance rates to ciprofloxacin (97.81%), ceftazidime (96.72%), gentamicin (91.26%), and amikacin (80.87%). Interestingly, colistin was found to be a potential drug of choice due to the high susceptibility of the tested isolates to this antimicrobial (87.98%). Most CRAB isolates in Thailand were of ST2 lineage, but some belonged to ST25, ST98, ST129, ST164, ST215, ST338, and ST745. Further studies to monitor the spread of carbapenem-resistant OXA-type β-lactamase genes from A. baumannii in hospital settings are warranted.

Emergence, molecular mechanisms and global spread of carbapenem-resistant Acinetobacter baumannii

Acinetobacter baumannii is a nosocomial pathogen that has emerged as a global threat because of high levels of resistance to many antibiotics, particularly those considered to be last-resort antibiotics, such as carbapenems. Although alterations in the efflux pump and outer membrane proteins can cause carbapenem resistance, the main mechanism is the acquisition of carbapenem-hydrolyzing oxacillinase-encoding genes. Of these, oxa23 is by far the most widespread in most countries, while oxa24 and oxa58 appear to be dominant in specific regions. Historically, much of the global spread of carbapenem resistance has been due to the dissemination of two major clones, known as global clones 1 and 2, although new lineages are now common in some parts of the world. The analysis of all publicly available genome sequences performed here indicates that ST2, ST1, ST79 and ST25 account for over 71 % of all genomes sequenced to date, with ST2 by far the most dominant type and oxa23 the most widespread carbapenem resistance determinant globally, regardless of clonal type. Whilst this highlights the global spread of ST1 and ST2, and the dominance of oxa23 in both clones, it could also be a result of preferential selection of carbapenem-resistant strains, which mainly belong to the two major clones. Furthermore, ~70 % of the sequenced strains have been isolated from five countries, namely the USA, PR China, Australia, Thailand and Pakistan, with only a limited number from other countries. These genomes are a vital resource, but it is currently difficult to draw an accurate global picture of this important superbug, highlighting the need for more comprehensive genome sequence data and genomic analysis.

The Current Burden of Carbapenemases: Review of Significant Properties and Dissemination among Gram-Negative Bacteria

Carbapenemases are β-lactamases belonging to different Ambler classes (A, B, D) and can be encoded by both chromosomal and plasmid-mediated genes. These enzymes represent the most potent β-lactamases, which hydrolyze a broad variety of β-lactams, including carbapenems, cephalosporins, penicillin, and aztreonam. The major issues associated with carbapenemase production are clinical due to compromising the activity of the last resort antibiotics used for treating serious infections, and epidemiological due to their dissemination into various bacteria across almost all geographic regions. Carbapenemase-producing Enterobacteriaceae have received more attention upon their first report in the early 1990s. Currently, there is increased awareness of the impact of nonfermenting bacteria, such as Acinetobacter baumannii and Pseudomonas aeruginosa, as well as other Gram-negative bacteria that are carbapenemase-producers. Outside the scope of clinical importance, carbapenemases are also detected in bacteria from environmental and zoonotic niches, which raises greater concerns over their prevalence, and the need for public health measures to control consequences of their propagation. The aims of the current review are to define and categorize the different families of carbapenemases, and to overview the main lines of their spread across different bacterial groups.

Molecular Epidemiology of Emerging Carbapenem Resistance in Acinetobacter nosocomialis and Acinetobacter pittii in Taiwan, 2010 to 2014

This study investigated the molecular epidemiology of carbapenem-resistant Acinetobacter nosocomialis and Acinetobacter pittii (ANAP). Clinical isolates of Acinetobacter spp.

This study investigated the molecular epidemiology of carbapenem-resistant Acinetobacter nosocomialis and Acinetobacter pittii (ANAP). Clinical isolates of Acinetobacter spp. collected by the biennial nationwide Taiwan Surveillance of Antimicrobial Resistance program from 2010 to 2014 were subjected to species identification, antimicrobial susceptibility testing, and PCR for detection of carbapenemase genes. Whole-genome sequencing or PCR mapping was performed to study the genetic surroundings of the carbapenemase genes. Among 1,041 Acinetobacter isolates, the proportion of ANAP increased from 11% in 2010 to 22% in 2014. The rate of carbapenem resistance in these isolates increased from 7.5% (3/40) to 22% (14/64), with a concomitant increase in their resistance to other antibiotics. The bla_OXA-72 and bla_OXA-58 genes were highly prevalent in carbapenem-resistant ANAP. Various genetic structures were found upstream of bla_OXA-58 in different plasmids. Among the plasmids found to contain bla_OXA-72 flanked by XerC/XerD, pAB-NCGM253-like was identified in 8 of 10 isolates. Conjugations of plasmids carrying bla_OXA-72 or bla_OXA-58 to A. baumannii were successful. In addition, three isolates with chromosome-located bla_OXA-23 embedded in AbGRI1-type structure with disruption of genes other than comM were detected. Two highly similar plasmids carrying class I integron containing bla_IMP-1 and aminoglycoside resistance genes were also found. The universal presence of bla_{OXA-272/213-like} on A. pittii chromosomes and their lack of contribution to carbapenem resistance indicate its potential to be a marker for species identification. The increase of ANAP, along with their diverse mechanisms of carbapenem resistance, may herald their further spread and warrants close monitoring.

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.