Genetic and Biochemical Characterization of FRI-1, a Carbapenem-Hydrolyzing Class A β-Lactamase from Enterobacter cloacae

An Enterobacter cloacae isolate was recovered from a rectal swab from a patient hospitalized in France with previous travel to Switzerland. It was resistant to penicillins, narrow- and broad-spectrum cephalosporins, aztreonam, and carbapenems but remained susceptible to expanded-spectrum cephalosporins. Whereas PCR-based identification of the most common carbapenemase genes failed, the biochemical Carba NP test II identified an Ambler class A carbapenemase. Cloning experiments followed by sequencing identified a gene encoding a totally novel class A carbapenemase, FRI-1, sharing 51 to 55% amino acid sequence identity with the closest carbapenemase sequences. However, it shared conserved residues as a source of carbapenemase activity. Purified β-lactamase FRI-1 hydrolyzed penicillins, aztreonam, and carbapenems but spared expanded-spectrum cephalosporins. The 50% inhibitory concentrations (IC₅₀s) of clavulanic acid and tazobactam were 10-fold higher than those found for Klebsiella pneumoniae carbapenemase (KPC), IMI, and SME, leading to lower sensitivity of FRI-1 activity to β-lactamase inhibitors. The bla_FRI-1 gene was located on a ca. 110-kb untypeable, transferable, and non-self-conjugative plasmid. A putative LysR family regulator-encoding gene at the 5′ end of the β-lactamase gene was identified, leading to inducible expression of the bla_FRI-1 gene.     

Genetic and Biochemical Characterization of OXA-405, an OXA-48-Type Extended-Spectrum β-Lactamase without Significant Carbapenemase Activity

The epidemiology of carbapenemases worldwide is showing that OXA-48 variants are becoming the predominant carbapenemase type in Enterobacteriaceae in many countries. However, not all OXA-48 variants possess significant activity toward carbapenems (e.g., OXA-163). Two Serratia marcescens isolates with resistance either to carbapenems or to extended-spectrum cephalosporins were successively recovered from the same patient. A genomic comparison using pulsed-field gel electrophoresis and automated Rep-PCR typing identified a 97.8% similarity between the two isolates. Both strains were resistant to penicillins and first-generation cephalosporins. The first isolate was susceptible to expanded-spectrum cephalosporins, was resistant to carbapenems, and had a significant carbapenemase activity (positive Carba NP test) related to the expression of OXA-48. The second isolate was resistant to expanded-spectrum cephalosporins, was susceptible to carbapenems, and did not express a significant imipenemase activity, (negative for the Carba NP test) despite possessing a bla_OXA-48-type gene. Sequencing identified a novel OXA-48-type β-lactamase, OXA-405, with a four-amino-acid deletion compared to OXA-48. The bla_OXA-405 gene was located on a ca. 46-kb plasmid identical to the prototype IncL/M bla_OXA-48-carrying plasmid except for a ca. 16.4-kb deletion in the tra operon, leading to the suppression of self-conjugation properties. Biochemical analysis showed that OXA-405 has clavulanic acid-inhibited activity toward expanded-spectrum activity without significant imipenemase activity. This is the first identification of a successive switch of catalytic activity in OXA-48-like β-lactamases, suggesting their plasticity. Therefore, this report suggests that the first-line screening of carbapenemase producers in Enterobacteriaceae may be based on the biochemical detection of carbapenemase activity in clinical settings.     

War Wound Treatment Complications Due to Transfer of an IncN Plasmid Harboring blaOXA-181 from Morganella morganii to CTX-M-27-Producing Sequence Type 131 Escherichia coli

A 22-year-old male developed a recurrent sacral abscess associated with embedded shrapnel following a blast injury. Cultures grew extended-spectrum β-lactamase (ESBL)-producing, carbapenem-susceptible Escherichia coli. Ertapenem was administered, but the infection recurred after each course of antibiotics. Initial surgical interventions were unsuccessful, and subsequent cultures yielded E. coli and Morganella morganii, both nonsusceptible to carbapenems. The isolates were Carba NP test negative, gave ambiguous results with the modified Hodge test, and amplified the bla_OXA48-like gene by real-time PCR. All E. coli isolates were sequence type 131 (ST131), carried nine resistance genes (including bla_CTX-M-27) on an IncF plasmid, and were identical by genome sequencing, except for 150 kb of plasmid DNA in carbapenem-nonsusceptible isolates only. Sixty kilobases of this was shared by M. morganii and represented an IncN plasmid harboring bla_OXA-181. In M. morganii, the gene was flanked by IS3000 and ISKpn19, but in all but one of the E. coli isolates containing bla_OXA-181, a second copy of ISKpn19 had inserted adjacent to IS3000. To the best of our knowledge, this is the first report of bla_OXA-181 in the virulent ST131 clonal group and carried by the promiscuous IncN family of plasmids. The tendency of M. morganii to have high MICs of imipenem, a bla_OXA-181 substrate profile that includes penicillins but not extended-spectrum cephalosporins, and weak carbapenemase activity almost resulted in the presence of bla_OXA-181 being overlooked. We highlight the importance of surveillance for carbapenem resistance in all species, even those with intrinsic resistances, and the value of advanced molecular techniques in detecting subtle genetic changes.     

Characterization of OXA-204, a Carbapenem-Hydrolyzing Class D β-Lactamase from Klebsiella pneumoniae

A Klebsiella pneumoniae clinical isolate recovered in Tunisia showed resistance to all β-lactams and decreased susceptibility to carbapenems. K. pneumoniae 204 expressed the carbapenem-hydrolyzing β-lactamase OXA-204, differing from OXA-48 by two amino acid substitutions (Gln98His and Thr99Arg) (class D β-lactamase [DBL] numbering). OXA-48 and OXA-204 shared similar resistance profiles, hydrolyzing carbapenems but sparing broad-spectrum cephalosporins. The bla_OXA-204 gene was located on a ca. 150-kb IncA/C-type plasmid, which also carried the bla_CMY-4 gene. The bla_OXA-204 gene was associated with an ISEcp1 element, whereas the bla_OXA-48 genes are usually associated with IS1999.     

Non-O1/Non-O139 Vibrio cholerae Avian Isolate from France Cocarrying the blaVIM-1 and blaVIM-4 Genes

We describe here a non-O1/non-O139 Vibrio cholerae isolate producing both VIM-1 and VIM-4 carbapenemases. It was isolated from a yellow-legged gull in southern France. The bla_VIM genes were part of a class 1 integron structure located in an IncA/C plasmid. This study emphasizes the presence of carbapenemase genes in wildlife microbiota.     

Emergence of KPC-2-Producing Pseudomonas aeruginosa Sequence Type 463 Isolates in Hangzhou,China

Thirty-nine Klebsiella pneumoniae carbapenemase (KPC)-producing Pseudomonas aeruginosa isolates, all exhibiting high-level resistance to carbapenems and other β-lactam antibiotics, were isolated in Hangzhou, China. Molecular epidemiology analysis indicated the presence of two dominant clones, namely, clones A and B, both of which belong to sequence type 463 (ST463). A genetic environment analysis demonstrated that both clones harbor an ISKpn8 transposase, bla_KPC-2, and an ISKpn6-like transposase. These findings depict the features of clonal expansion and transmission of KPC-2-producing P. aeruginosa strains in Hangzhou, China.     

First report of the isolation of blaIMI-1-producing colistin-heteroresistant Enterobacter cloacae in Japan,September 2016

The isolation of a carbapenem-resistant Enterobacter cloacae strain harboring the IMI-1 variant of bla_IMI-1 carbapenemase points to the worldwide emergence of multidrug resistant bacteria as a potential source of health care infections. In this report, we describe the first isolation of E. cloacae with bla_IMI-1 carbapenemase isolated from a Japanese patient in September 2016. The isolate was resistant to carbapenems, levofloxacin, and aminoglycosides, and heteroresistant to colistin but sensitive to fourth-generation cephalosporins. All microbiology laboratories worldwide should be made aware of these bla_IMI-1-producing subtypes with unusual antibiotic susceptibility profiles.     

dd-Carboxypeptidase and Peptidoglycan Transpeptidase from Pseudomonas aeruginosa

Peptidoglycan transpeptidase and dd-carboxypeptidase have been detected in isolated membranes of Pseudomonas aeruginosa. Cephalosporins and penicillins fail to inhibit the transpeptidase at concentrations as high as 100 μg/ml. dd-Carboxypeptidase, on the other hand, is sensitive to inhibition by β-lactam antibiotics. The presence of dimethyl sulfoxide in the reaction mixture results in a twofold stimulation of peptidoglycan formation, whereas dd-carboxypeptidase is inhibited approximately 30%. Maximum stimulation of transpeptidase occurs in the presence of both dimethyl sulfoxide and a β-lactum antibiotic. This is in sharp contrast to the transpeptidase from Escherichia coli, which is sensitive to inhibition by penicillins and cephalosporins.     

Novel Ambler Class A Carbapenem-Hydrolyzing β-Lactamase from a Pseudomonas fluorescens Isolate from the Seine River,Paris, France

A Pseudomonas fluorescens isolate (PF-1) resistant to carbapenems was recovered during an environmental survey performed with water from the Seine River (Paris). It expressed a novel Ambler class A carbapenemase, BIC-1, sharing 68 and 59% amino acid identities with β-lactamases SFC-1 from Serratia fonticola and the plasmid-encoded KPC-2, respectively. β-Lactamase BIC-1 hydrolyzed penicillins, carbapenems, and cephalosporins except ceftazidime and monobactams. The bla_BIC-1 gene was chromosomally located and was also identified in two other P. fluorescens strains isolated from the Seine River 3 months later.Pseudomonas fluorescens is a psychrotrophic bacterium that expresses a chromosomally encoded and inducible Ambler class C β-lactamase (10, 15). Carbapenemases (serine- or metallo-β-lactamases) remain the most common mechanism of resistance to carbapenems in Gram-negative organisms (22, 23). To date, most acquired metallo-β-lactamase (MBL)-encoding genes (bla_IMP or bla_VIM variants) have been reported from Pseudomonas aeruginosa and very rarely from P. fluorescens (8, 12). Class A carbapenemases are either chromosome encoded or plasmid encoded and remain rarely identified in Gram-negative organisms. Indeed, several class A carbapenemases are chromosomally encoded (NMC-A, SFC-1, SME-1 to -3, IMI-1), with the exception of the emerging KPC β-lactamases, which are plasmid encoded (24). The chromosomal location of the bla_SFC-1 gene could be the result of a horizontal gene transfer into an environmental Serratia fonticola isolate (5). The bla_SME genes from Serratia marcescens are presumed to be chromosomal. Genes encoding NMC-A and IMI β-lactamases have been found sporadically, either in clinical or in environmental isolates of Enterobacter cloacae and Enterobacter asburiae from rivers (2). The bla_NMC-A gene was found chromosomally located in several clinical isolates. The bla_IMI-1 gene was chromosomally located, whereas the bla_IMI-2 genes were identified on plasmids. The imiR-imi-2 gene tandem in E. cloacae and E. asburiae appeared to be flanked by transposable elements (2). Class A carbapenemases such as GES-2, GES-5, and KPC-2 have been recently reported from P. aeruginosa (16) but not from other Pseudomonas species.Here, we characterize a novel class A carbapenemase identified from a P. fluorescens environmental isolate. This identification occurred during a survey aimed to study the spread of multidrug-resistant Gram-negative organisms in the environment.     

Characterization of BKC-1 Class A Carbapenemase from Klebsiella pneumoniae Clinical Isolates in Brazil

Three Klebsiella pneumoniae clinical isolates demonstrating carbapenem resistance were recovered from different patients hospitalized at two medical centers in São Paulo, Brazil. Resistance to all β-lactams, quinolones, and some aminoglycosides was observed for these isolates that were susceptible to polymyxin B. Carbapenem hydrolysis, which was inhibited by clavulanic acid, was observed for all K. pneumoniae isolates that belonged to the same pulsed-field gel electrophoresis (PFGE) type and a novel sequence type (ST), ST1781 (clonal complex 442 [CC442]). A 10-kb nonconjugative incompatibility group Q (IncQ) plasmid, denominated p60136, was transferred to Escherichia coli strain TOP10 cells by electroporation. The full sequencing of p60136 showed that it was composed of a mobilization system, ISKpn23, the phosphotransferase aph3A-VI, and a 941-bp open reading frame (ORF) that codified a 313-amino acid protein. This ORF was named bla_BKC-1. Brazilian Klebsiella carbapenemase-1 (BKC-1) showed a pI of 6.0 and possessed the highest identity (63%) with a β-lactamase of Sinorhizobium meliloti, an environmental bacterium. Hydrolysis studies demonstrated that purified BKC-1 not only hydrolyzed carbapenems but also penicillins, cephalosporins, and monobactams. However, the carbapenems were less efficiently hydrolyzed due to their very low k_cat values (0.0016 to 0.031 s⁻¹). In fact, oxacillin was the best substrate for BKC-1 (k_cat/K_m, 53,522.6 mM⁻¹ s⁻¹). Here, we report a new class A carbapenemase, confirming the diversity and rapid evolution of β-lactamases in K. pneumoniae clinical isolates.     

Genetic Factors Associated with Elevated Carbapenem Resistance in KPC-Producing Klebsiella pneumoniae

In the United States, the most prevalent mechanism of carbapenem resistance among Enterobacteriaceae is the production of a Klebsiella pneumoniae carbapenemase (KPC). KPC-producing isolates often exhibit a range of carbapenem MICs. To better understand the factors that contribute to overall carbapenem resistance, we analyzed 27 KPC-producing K. pneumoniae isolates with different levels of carbapenem resistance, 11 with low-level (i.e., meropenem or imipenem MIC ≤ 4 μg/ml), 2 with intermediate-level (i.e., meropenem and imipenem MIC = 8 μg/ml), and 14 with high-level (i.e., imipenem or meropenem MIC ≥ 16 μg/ml) carbapenem resistance, that were received from throughout the United States. Among 14 isolates that exhibited high-level carbapenem resistance, Western blot analysis indicated that 10 produced an elevated amount of KPC. These isolates either contained an increased bla_KPC gene copy number (n = 3) or had deletions directly upstream of the bla_KPC gene (n = 7). Four additional isolates lacked elevated KPC production but had high-level carbapenem resistance. Porin sequencing analysis identified 22 isolates potentially lacking a functional OmpK35 and three isolates potentially lacking a functional OmpK36. The highest carbapenem MICs were found in two isolates that lacked both functioning porins and produced elevated amounts of KPC. The 11 isolates with low-level carbapenem resistance contained neither an upstream deletion nor increased bla_KPC copy number. These results suggest that both bla_KPC copy number and deletions in the upstream genetic environment affect the level of KPC production and may contribute to high-level carbapenem resistance in KPC-producing K. pneumoniae, particularly when coupled with OmpK36 porin loss.The occurrence of Gram-negative bacterial infections that are resistant to extended-spectrum β-lactam antimicrobial agents forces clinicians to rely on carbapenems as a “last resort” to combat these resistant pathogens. However, as carbapenems are more frequently utilized, an increasing number of bacteria with various mechanisms of resistance to this class of antimicrobial agents are identified. The most widespread resistance mechanisms include the production of a carbapenemase and the combination of porin loss with the production of either an AmpC enzyme or an extended-spectrum β-lactamase (4, 15). Klebsiella pneumoniae carbapenemase (KPC), an Ambler class A β-lactamase that can hydrolyze most β-lactam agents, including carbapenems, is now the most prevalent carbapenemase found among clinical Gram-negative isolates in the United States (22).KPC was first reported in a K. pneumoniae isolate from North Carolina in 1996 (28). However, recent reports indicate that KPC-producing Gram-negative isolates are being identified throughout the United States as well as parts of Europe, Asia, and South America (13, 20, 22). Although these β-lactamases occur most commonly in K. pneumoniae, they have also been identified in other members of the Enterobacteriaceae family and in Pseudomonas and Acinetobacter species (3, 21, 24, 26, 27). The bla_KPC gene is plasmid mediated and is carried on a Tn3-based transposon, Tn4401 (17), which may account for the high mobility of this resistance mechanism.KPC-producing isolates can exhibit a range of carbapenem MICs, thus making their detection a significant challenge for clinical laboratories. By using 2009 Clinical and Laboratory Standards Institute (CLSI) breakpoints and testing methods (1, 6), some KPC-producing isolates may be identified as susceptible to carbapenems. The clinical significance of carbapenem-susceptible isolates with elevated carbapenem MICs is unclear (6), and the cellular changes that may convert a susceptible KPC-producing isolate to one with MICs indicating resistance to carbapenem are not well described. From previous reports, we know that KPC production combined with porin loss can result in higher carbapenem MICs (10, 14, 29). This finding suggests that the KPC enzyme alone is not always sufficient to confer carbapenem resistance, as defined by the 2009 CLSI breakpoints.Other factors likely result in higher carbapenem MICs for KPC-producing isolates. For example, isolates with an increased expression of bla_KPC were previously shown to have increased rates of hydrolysis of imipenem and meropenem (14). Directly upstream of the bla_KPC gene is a nonconserved region of the Tn4401 transposon, located between the istB and the bla_KPC genes (17). Previous reports describe four isoforms in this variable region: Tn4401a contains a 100-bp deletion, Tn4401b contains no deletion (17), and isoforms with 215-bp (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"DQ989640","term_id":"116263782","term_text":"DQ989640"}}DQ989640) and 255-bp (13) deletions were recently reported. Additional studies of this variable region suggest that the 100-bp deletion may result in a different −35 promoter region of the bla_KPC gene (11). Upstream deletions that affect the promoter may impact the level of bla_KPC expression and thus would influence the overall level of carbapenem resistance. Also, KPC-producing isolates may contain different levels of bla_KPC dosage based on the presence of multiple copies of a bla_KPC-carrying plasmid, multiple bla_KPC-carrying plasmids, or multiple copies of the bla_KPC gene located within the same plasmid (11). Increasing the bla_KPC gene copy number could result in increased enzyme production and higher carbapenem MICs. Understanding the impact of these factors may help to predict the potential for KPC-producing isolates susceptible to carbapenems to convert to isolates resistant to carbapenems.In this study, we examined genetic factors that may enhance the level of carbapenem resistance. We selected 27 KPC-producing K. pneumoniae isolates that were obtained from clinical patients in different areas of the country and exhibited a range of carbapenem MICs. These isolates were characterized by determining the sequences of the two main porins, OmpK35 and OmpK36 (9), examining levels of KPC production by Western blot analysis, comparing relative bla_KPC copy numbers using quantitative real-time PCR, and analyzing sequence variations in the genetic environment directly upstream of the bla_KPC gene.     

Double Mutation in the pfmdr1 Gene Is Associated with Emergence of Chloroquine-Resistant Plasmodium falciparum Malaria in Eastern India

Malaria is a major public health problem in tropical and subtropical countries, including India. This study elucidates the cause of chloroquine treatment failure (for Plasmodium falciparum infection) before the introduction of artemisinin combination therapy. One hundred twenty-six patients were randomized to chloroquine treatment, and the therapeutic efficacy was monitored from days 1 to 28. An in vitro susceptibility test was performed with all isolates. Parasitic DNA was isolated, followed by PCR and restriction digestion of different codons of the pfcrt gene (codons 72 to 76) and the pfmdr1 gene (N86Y, Y184F, S1034C, N1042D, and D1246Y). Finally, sequencing was done to confirm the mutations. Forty-three (34.13%) early treatment failure cases and 16 (12.69%) late treatment failure cases were observed after chloroquine treatment. In vitro chloroquine resistance was found in 103 isolates (81.75%). Twenty-six (60.47%) early treatment failure cases and 6 (37.5%) late treatment failure cases were associated with the CVMNK-YYSNY allele (the underlined amino acids are those that were mutated). Moreover, the CVIEK-YYSNY allele was found in 8 early treatment failure (18.60%) and 2 late treatment failure (12.5%) cases. The presence of the wild-type pfcrt (CVMNK) and pfmdr1 (YYSNY) double mutant allele in chloroquine-nonresponsive cases was quite uncommon. In vivo chloroquine treatment failure and in vitro chloroquine resistance were strongly correlated with the CVMNK-YYSNY and CVIEK-YYSNY haplotypes (P < 0.01).     

Mobile Genetic Elements Related to the Diffusion of Plasmid-Mediated AmpC β-Lactamases or Carbapenemases from Enterobacteriaceae: Findings from a Multicenter Study in Spain

We examined the genetic context of 74 acquired ampC genes and 17 carbapenemase genes from 85 of 640 Enterobacteriaceae isolates collected in 2009. Using S1 pulsed-field gel electrophoresis and Southern hybridization, 37 of 74 bla_AmpC genes were located on large plasmids of different sizes belonging to six incompatibility groups. We used sequencing and PCR mapping to investigate the regions flanking the acquired ampC genes. The bla_CMY-2-like genes were associated with ISEcp1; the surrounding bla_DHA genes were similar to Klebsiella pneumoniae plasmid pTN60013 associated with IS26 and the psp and sap operons; and the bla_ACC-1 genes were associated with IS26 elements inserted into ISEcp1. All of the carbapenemase genes (bla_VIM-1, bla_IMP-22, and bla_IMP-28) were located in class 1 integrons. Therefore, although plasmids are the main cause of the rapid dissemination of ampC genes among Enterobacteriaceae, we need to be aware that other mobile genetic elements, such as insertion sequences, transposons, or integrons, can be involved in the mobilization of these genes of chromosomal origin. Additionally, three new integrons (In846 to In848) are described in this study.     

Emergence and Distribution of Plasmids Bearing the blaOXA-51-Like Gene with an Upstream ISAba1 in Carbapenem-Resistant Acinetobacter baumannii Isolates in Taiwan

The bla_OXA-51-like gene with an upstream ISAba1 (ISAba1-bla_OXA-51-like gene) was originally found on the chromosomes of carbapenem-resistant or -susceptible Acinetobacter baumannii isolates. However, a plasmid-borne ISAba1-bla_OXA-51-like gene has recently been identified in Acinetobacter genomic species 13TU and several A. baumannii isolates in Taiwan, and all of the isolates are carbapenem resistant. This study aimed to characterize the plasmids bearing the ISAba1-bla_OXA-51-like gene and their significance in A. baumannii. Among the 117 ISAba1-bla_OXA-51-like-harboring isolates collected from 10 hospitals in Taiwan, 58 isolates (49.6%) from 24 clones had the genes located on plasmids that likely originated from a common progenitor. Among the 58 isolates, four had additional copy of the ISAba1-bla_OXA-51-like gene on their chromosomes. Based on the analysis of these four isolates, the plasmid-located ISAba1-bla_OXA-51-like gene appeared to be acquired via one-ended transposition (Tn6080). The isolates with a plasmid bearing the ISAba1-bla_OXA-51-like gene had higher rates of resistance to imipenem (98% versus 46.6%; P < 0.001) and meropenem (98% versus 69%; P = 0.019) than those with the genes chromosomally encoded, which is most likely due to increased gene dosage provided by the higher copy number of associated plasmids. Transformation with a recombinant plasmid harboring only the ISAba1-bla_OXA-51-like gene was enough to confer a high level of carbapenem resistance to A. baumannii, eliminating the possible contribution of other factors on the original plasmids. This study demonstrated that the carbapenem resistance-associated plasmids carrying the ISAba1-bla_OXA-51-like gene are widespread in A. baumannii strains in Taiwan.Acinetobacter baumannii has emerged as a major pathogen of nosocomial infections in immunocompromised patients and is associated with a high mortality rate (7). The management of this pathogen has become a significant challenge due to the increased emergence of carbapenem-resistant strains (19, 22). It has been shown that most of the carbapenem resistance in A. baumannii is due to the production of carbapenemases, especially those belonging to carbapenem-hydrolyzing class D beta-lactamases (CHDLs), which are encoded by the bla_OXA-51-like, bla_OXA-23-like, bla_OXA-24-like, and bla_OXA-58-like genes (19). Among these CHDL genes, the bla_OXA-51-like gene is intrinsic to and was originally located on the chromosome of A. baumannii (7, 18, 24).The CHDLs have only a weak carbapenem-hydrolyzing activity (1, 19). However, overexpression of these CHDL genes, driven mostly by promoters provided by their upstream insertion sequences (ISs), is one of the means by which A. baumannii acquires a high level of carbapenem resistance. For example, ISAba1 upstream of the bla_OXA-51-like gene is associated with the overexpression of the bla_OXA-51-like gene and carbapenem resistance in A. baumannii (12, 23). However, some isolates harboring the bla_OXA-51-like gene with an upstream ISAba1 (ISAba1-bla_OXA-51-like gene) are still susceptible to carbapenem (9, 14, 16). The reason for this discrepancy in carbapenem susceptibility levels in isolates harboring the ISAba1-bla_OXA-51-like gene has not been completely clarified. In some isolates, the high level of resistance might be due to interplay between the overexpression of the bla_OXA-51-like gene and other mechanisms, such as overexpression of an efflux pump (12, 19). However, the overexpression of the CHDL genes by themselves can occasionally confer a high level of carbapenem resistance, especially when the resistance determinants are located on a plasmid, and this is likely due to the higher gene dosage provided by the higher copy number associated with plasmids (3). Recently, we have identified several A. baumannii isolates in Taiwan that harbor plasmid-borne ISAba1-bla_OXA-51-like genes (ISAba1-bla_OXA-82) (GenBank accession no. {"type":"entrez-nucleotide","attrs":{"text":"GQ352402","term_id":"255076961","term_text":"GQ352402"}}GQ352402). Moreover, a plasmid bearing the ISAba1-bla_OXA-51-like gene (ISAba1-bla_OXA-138) has also been indentified in an Acinetobacter genomic species 13TU isolate (15). The mobilization of the ISAba1-bla_OXA-51-like gene to plasmids and dissemination of these plasmids will further complicate the management of A. baumannii infections. This study aimed to characterize the spread of these plasmids and their significance in A. baumannii isolates in Taiwan.     

Molecular Characterization of ISCR1-Mediated blaPER-1 in a Non-O1, Non-O139 Vibrio cholerae Strain from China

We report the detection of PER-1 extended-spectrum β-lactamase (ESBL) in a clinical non-O1, non-O139 Vibrio cholerae strain from China. ISCR1-mediated bla_PER-1 was embedded in a complex In4 family class 1 integron belonging to the lineage of Tn1696 on a conjugative IncA/C plasmid. A free 8.98-kb circular molecule present with the ISCR1-bla_PER-1–truncated 3′-conserved sequence (CS) structure was detected in this isolate. These findings may provide insight into the mobilization of bla_PER-1.