In vitro prediction of the evolution of GES-1 β-lactamase hydrolytic activity

Phylogenetic predictions of carbapenemase activity from the Guiana extended-spectrum (GES) family of β-lactamases

Objectives

We investigated the amino acid substitutions in the GES family of ESBLs that were most likely to be involved in the evolution of carbapenemase activity.

Methods

To identify the substitutions that are functionally important, we analysed the evolutionary history of the GES β-lactamases using an alignment and phylogeny to identify sites in GES that show evidence of positive selection and the selected phenotypes.

Results and Conclusions

Data indicate that the substitutions G170S and G243A are associated with carbapenemase activity. The substitutions Q43E, E104K and T237A are most likely associated with ESBL activity.

Municipal wastewater monitoring revealed the predominance of bla GES genes with diverse variants among carbapenemase-producing organisms: high occurrence and persistence of Aeromonas caviae harboring the new bla GES variant bla GES-48

IMPORTANCE

The emergence and spread of carbapenemase-producing organisms (CPOs) represent a global health threat because they are associated with limited treatment options and poor clinical outcomes. Wastewater is considered a hotspot for the evolution and dissemination of antimicrobial resistance. Thus, analyses of municipal wastewater are critical for understanding the circulation of these CPOs and carbapenemase genes in local communities, which remains scarcely known in Japan. This study resulted in several key observations: (i) the vast majority of bla GES genes, including six new bla GES variants, and less frequent bla IMP genes were carbapenemase genes encountered exclusively in wastewater influent; (ii) the most dominant CPO species were Aeromonas spp., in which a remarkable diversity of new sequence types was observed; and (iii) CPOs were detected from combined sewer wastewater, but not from separate sewer wastewater, suggesting that the load of CPOs from unrecognized environmental sources could greatly contribute to their detection in influent wastewater.

A panel of diverse Klebsiella pneumoniae clinical isolates for research and development

Klebsiella pneumoniae are a leading cause of healthcare-associated infections worldwide. In particular, strains expressing extended-spectrum β-lactamases (ESBLs) and carbapenemases pose serious treatment challenges, leading the World Health Organization (WHO) to designate ESBL and carbapenem-resistant Enterobacteriaceae as 'critical' threats to human health. Research efforts to combat these pathogens can be supported by accessibility to diverse and clinically relevant isolates for testing novel therapeutics. Here, we describe a panel of 100 diverse K. pneumoniae isolates that are publicly available to assist the research community in this endeavour. Whole-genome sequencing (WGS) was performed on 3878 K. pneumoniae clinical isolates housed at the Multidrug-Resistant Organism Repository and Surveillance Network. The isolates were cultured from 63 facilities in 19 countries between 2001 and 2020. Core-genome multilocus sequence typing and high-resolution single-nucleotide polymorphism-based phylogenetic analyses captured the genetic diversity of the collection and were used to select the final panel of 100 isolates. In addition to known multidrug-resistant (MDR) pandemic lineages, the final panel includes hypervirulent lineages and isolates with specific and diverse resistance genes and virulence biomarkers. A broad range of antibiotic susceptibilities, ranging from pan-sensitive to extensively drug-resistant isolates, are described. The panel collection, and all associated metadata and genome sequences, are available at no additional cost and will be an important resource for the research community and for the design and development of novel antimicrobial agents and diagnostics against this important pathogen.

Genome-wide analysis reveals the emergence of multidrug resistant Stenotrophomonas acidaminiphila strain SINDOREI isolated from a patient with sepsis

Stenotrophomonas acidaminiphila, the most recent reported species in genus Stenotrophomonas, is a relatively rare bacteria and is an aerobic, glucose non-fermentative, Gram-negative bacterium. However, little information of S. acidaminiphila is known to cause human infections. In this research, we firstly reported a multidrug-resistant strain S. acidaminiphila SINDOREI isolated from the blood of a patient with sepsis, who was dead of infection eventually. The whole genome of strain SINDOREI was sequenced, and genome comparisons were performed among six closely related S. acidaminiphila strains. The core genes (2,506 genes) and strain-specific genes were identified, respectively, to know about the strain-level diversity in six S. acidaminiphila stains. The presence of a unique gene (narG) and essential genes involved in biofilm formation in strain SINDOREI are important for the pathogenesis of infections. Strain SINDOREI was resistant to trimethoprim/sulfamethoxazole, ciprofloxacin, ofloxacin, cefepime, ceftazidime, and aztreonam. Several common and specific antibiotic resistance genes were identified in strain SINDOREI. The presence of two sul genes and exclusive determinants GES-1, aadA3, qacL, and cmlA5 is responsible for the resistance to multidrug. The virulence factors and resistance determinants can show the relationship between the phenotype and genotype and afford potential therapeutic strategies for infections.

In vivo translational assessment of the GES genotype on the killing profile of ceftazidime, ceftazidime/avibactam and meropenem against Pseudomonas aeruginosa

Objectives

To evaluate the in vivo killing profile of human-simulated exposures of ceftazidime, ceftazidime/avibactam and meropenem against GES-harbouring Pseudomonas aeruginosa in the murine thigh infection model.

Methods

Five P. aeruginosa isolates [three isogenic (GES-1, GES-5 and GES-15) and two clinical (GES-5 and GES-15)] were evaluated. MICs were determined using broth microdilution. Human-simulated regimens (HSRs) of ceftazidime 2 g IV q8h as a 2 h infusion, ceftazidime/avibactam 2.5 g IV q8h as a 2 h infusion and meropenem 2 g IV q8h as a 3 h infusion were administered. Change in bacterial burden relative to baseline was assessed.

Results

Modal MICs ranged from 8 to >64 mg/L for ceftazidime, from 1 to 16 mg/L for ceftazidime/avibactam and from 1 to >64 mg/L for meropenem. In vivo, for the isogenic strains, avibactam augmented ceftazidime activity against the GES-1- and GES-15-harbouring isolates. Both ceftazidime and ceftazidime/avibactam resulted in significant kill against the GES-5 isogenic isolate. The meropenem HSR produced >1 log₁₀ kill against each isogenic isolate (MICs of 1–4 mg/L). Against the GES-5 clinical isolate, ceftazidime and ceftazidime/avibactam resulted in >1 log₁₀ kill compared with bacterial growth with the meropenem HSR. In the clinical isolate harbouring GES-15, the elevated MICs of ceftazidime and ceftazidime/avibactam reduced the effectiveness of both compounds, while the observed reduction in meropenem MIC translated into in vivo efficacy of the HSR regimen, predictive of clinical efficacy.

Conclusions

In GES-harbouring P. aeruginosa, quantitative reductions in bacterial density observed with the translational murine model suggest that the phenotypic profile of ceftazidime, ceftazidime/avibactam and meropenem is predictive of clinical efficacy when using the evaluated dosing regimens.

Characterization of a Novel Plasmid in Serratia marcescens Harbouring blaGES-5 Isolated from a Nosocomial Outbreak in Japan

Serratia marcescens is a nosocomial pathogen with carbapenem resistance, which limits the availability of effective treatment options. In this study, we performed molecular characterization of GES-5 carbapenemase-producing S. marcescens isolated from an outbreak in Japan. Comparative genetic analysis revealed that the bla_GES-5-encoding plasmid p2020-O-9 is a unique plasmid contributing to carbapenem resistance. Furthermore, this study highlights the necessity of surveillance programs for monitoring novel, along with commonly occurring carbapenemases in clinical settings.

Extended Spectrum Beta-Lactamase (ESBL) Produced by Gram-Negative Bacteria in Trinidad and Tobago

Gram-negative bacterial infections are a global health problem. The production of beta-lactamase is still the most vital factor leading to beta-lactam resistance. In Trinidad and Tobago, extended spectrum beta-lactamase (ESBL) production has been detected and reported mainly in the isolates of Klebsiella pneumoniae and Escherichia coli and constitutes a public health emergency that causes high morbidity and mortality in some patients. In this literature review, the authors cover vast information on ESBL frequency and laboratory detection using both conventional and molecular methods from clinical data. The aim is to make the reader reflect on how the actual knowledge can be used for rapid detection and understanding of the spread of antimicrobial resistance problems stemming from ESBL production among common Gram-negative organisms in the health care system.

In Vivo Evolution of GES β-Lactamases Driven by Ceftazidime/Avibactam Treatment of Pseudomonas aeruginosa Infections

The mechanisms underlying an in vivo switch in the resistance phenotype of P. aeruginosa after ceftazidime-avibactam treatment was investigated. The initial isolate (a blood culture) was resistant to meropenem but remained susceptible to antipseudomonal cephalosporins and combinations with β-lactamase inhibitors. One week after ceftazidime-avibactam therapy, a subsequent isolate (a rectal swab) recovered from the same patient showed the opposite phenotype. Whole-genome sequence analysis revealed a single SNP difference between both (ST235) isolates, leading to a P162S change in bla_GES-5, creating bla_GES-15. Thus, bla_GES-1, bla_GES-5, and bla_GES-15 were cloned and expressed in the wild-type strain PAO1. Susceptibility profiles confirmed the P162S substitution reverted the carbapenemase phenotype determined by the G170S change of GES-5 back into the ESBL phenotype of GES-1.

Extended-spectrum β-lactamases: an update on their characteristics, epidemiology and detection

Extended-spectrum β-lactamase (ESBL)-producing Gram-negative pathogens are a major cause of resistance to expanded-spectrum β-lactam antibiotics. Since their discovery in the early 1980s, they have spread worldwide and an are now endemic in Enterobacterales isolated from both hospital-associated and community-acquired infections. As a result, they are a global public health concern. In the past, TEM- and SHV-type ESBLs were the predominant families of ESBLs. Today CTX-M-type enzymes are the most commonly found ESBL type with the CTX-M-15 variant dominating worldwide, followed in prevalence by CTX-M-14, and CTX-M-27 is emerging in certain parts of the world. The genes encoding ESBLs are often found on plasmids and harboured within transposons or insertion sequences, which has enabled their spread. In addition, the population of ESBL-producing Escherichia coli is dominated globally by a highly virulent and successful clone belonging to ST131. Today, there are many diagnostic tools available to the clinical microbiology laboratory and include both phenotypic and genotypic tests to detect β-lactamases. Unfortunately, when ESBLs are not identified in a timely manner, appropriate antimicrobial therapy is frequently delayed, resulting in poor clinical outcomes. Several analyses of clinical trials have shown mixed results with regards to whether a carbapenem must be used to treat serious infections caused by ESBLs or whether some of the older β-lactam-β-lactamase combinations such as piperacillin/tazobactam are appropriate. Some of the newer combinations such as ceftazidime/avibactam have demonstrated efficacy in patients. ESBL-producing Gram-negative pathogens will continue to be major contributor to antimicrobial resistance worldwide. It is essential that we remain vigilant about identifying them both in patient isolates and through surveillance studies.

Multidrug-resistant Klebsiella pneumoniae: mechanisms of resistance including updated data for novel β-lactam-β-lactamase inhibitor combinations

Introduction: Multi-drug-resistant Klebsiella pneumoniae is currently one of the most pressing emerging issues in bacterial resistance. Treatment of K.pneumoniae infections is often problematic due to the lack of available therapeutic options, with a relevant impact in terms of morbidity, mortality and healthcare-associated costs. Soon after the launch of Ceftazidime-Avibactam, one of the approved new β-lactam/β-lactamase inhibitor combinations, reports of ceftazidime-avibactam-resistant strains developing resistance during treatment were published. Being a hospital-associated pathogen, K.pneumoniae is continuously exposed to multiple antibiotics resulting in constant selective pressure, which in turn leads to additional mutations that are positively selected.Areas covered: Herein the authors present the K.pneumoniae mechanisms of resistance to different antimicrobials, including updated data for ceftazidime-avibactam.Expert opinion: K.pneumoniae is a nosocomial pathogen commonly implicated in hospital outbreaks with a propensity for antimicrobial resistance toward mainstay β-lactam antibiotics and multiple other antibiotic classes. Following the development of drug resistance and understanding the mechanisms involved, we can improve the efficacy of current antimicrobials, by applying careful stewardship and rational use to preserve their potential utility. The knowledge on antibiotic resistance mechanisms should be used to inform the design of novel therapeutic agents that might not be subject to, or can circumvent, mechanisms of resistance.

Activity of carbonyl cyanide-3-chlorophenylhydrazone on biofilm formation and antimicrobial resistance in Pseudomonas aeruginosa using quantum dots-meropenem conjugates as nanotools

Hospital infections associated with multidrug-resistant (MDR) Pseudomonas aeruginosa are a worldwide public health problem. Efflux systems and biofilm formation are mechanisms related to resistance to carbapenemics. In this study, quantum dots (QDs) were used to evaluate the effect of carbonyl cyanide-3-chlorophenylhydrazone (CCCP), an efflux pump system inhibitor, on biofilm formation and antimicrobial resistance profile of P. aeruginosa strains. For this, QDs were covalently conjugated to meropenem (MPM) and incubated with a P. aeruginosa resistant isolate (P118) or a control sensitive strain (ATCC Pa27853). P118 was also analyzed with conjugates after previous CCCP efflux inhibitor incubation. Fluorescence microscopy images showed that both sensitive and resistant bacteria were efficiently labeled. Nevertheless, P118 isolates presented fluorescent cell agglomerates, suggesting biofilm formation. The addition of the CCCP changed the labeling profile of the resistant isolate, and the absence of agglomerates was observed, indicating no biofilm formation. Genetic assays revealed the presence of MexA and MexE genes encoding channel proteins from efflux pump systems in both resistant and sensitive strains. Disk-diffusion and broth microdilution tests determined drug susceptibility profiles in the presence and absence of CCCP for P118 isolates. We verified that the CCCP efflux system inhibitor may contribute to P. aeruginosa resistant phenotype reduction for some antimicrobials. This study verified the efficiency of QD-MPM conjugates to trigger and study biofilm formation, or its inhibition, before and after CCCP addition. QDs conjugated to antimicrobials can be used as nanotools to investigate multidrug-resistant bacterial strains on biofilm formation.

ESBLs and resistance to ceftazidime/avibactam and ceftolozane/tazobactam combinations in Escherichia coli and Pseudomonas aeruginosa

OBJECTIVES

To evaluate the efficacy of the recently launched β-lactam/β-lactamase inhibitor combinations ceftazidime/avibactam and ceftolozane/tazobactam against ESBL-producing Escherichia coli and Pseudomonas aeruginosa strains.

METHODS

A series of ESBL-encoding genes (blaTEM, blaSHV, blaCTX-M, blaVEB, blaPER, blaGES and blaBEL) was cloned and expressed in E. coli or P. aeruginosa recipient strains. Cultures of E. coli TOP10 harbouring recombinant plasmids and therefore producing the different ESBLs tested were grown in order to perform measurements of catalytic activities, using benzylpenicillin, ceftazidime and ceftolozane as substrates. IC50s were additionally determined for clavulanic acid, tazobactam and avibactam.

RESULTS

We showed here an overall better activity of ceftazidime/avibactam compared with ceftolozane/tazobactam toward ESBL-producing E. coli and P. aeruginosa. Several ESBLs of the GES, PER and BEL types conferred resistance to ceftolozane/tazobactam in E. coli and P. aeruginosa. For GES-6 and PER-1 producers, resistance to ceftolozane/tazobactam could be explained by a high hydrolysis of ceftolozane and a low activity of tazobactam as an inhibitor. On the other hand, PER-producing P. aeruginosa also exhibited resistance to ceftazidime/avibactam.

CONCLUSIONS

Altogether, the results show that the ESBL PER-1, which is widespread worldwide, may be a source of resistance to both ceftolozane/tazobactam and ceftazidime/avibactam. Excellent activity of ceftazidime/avibactam was highlighted for both ESBL-producing E. coli and ESBL-producing P. aeruginosa.

A disposable gold-cellulose nanofibril platform for SERS mapping

In this study, we present a disposable and inexpensive paper-like gold nanoparticle-embedded cellulose nanofibril substrate for the rapid enumeration of Escherichia coli (E. coli) using surface-enhanced Raman scattering (SERS) mapping. A disposable SERS substrate was simply constructed by mixing CNF and gold chloride solution at 120 °C in a water bath. The application of the resulting substrate was carried out by enrichment and SERS detection of E. coli. To this end, the spherical gold nanoparticle-embedded cellulose nanofibril substrate was used as a scavenger for E. coli. After the target bacteria E. coli were separated from the matrix via oriented antibodies, the sandwich assay procedure was carried out using 5,5-dithiobis-(2-nitrobenzoic acid) (DTNB)-coated Au nanorod particles that acted as SERS mapping probes. The distribution density of DTNB was demonstrated visually using SERS mapping, and the assay was completed in one hour. The correlation between the E. coli and SERS mapping signals was found to be linear within the range of 15 cfu mL-1 to 1.5 × 105 cfu mL-1. The limit of detection for the SERS mapping assay was determined to be 2 cfu mL-1. The selectivity of the developed method was examined with Micrococcus luteus (M. luteus), Bacillus subtilis (B. subtilis), and Enterobacter aerogenes (E. aerogenes), which did not produce any significant response. Furthermore, the developed method was evaluated for detecting E. coli in artificially contaminated samples, and the results were compared with those of the plate-counting method.

Acquisition of Extended-Spectrum β-Lactamase GES-6 Leading to Resistance to Ceftolozane-Tazobactam Combination in Pseudomonas aeruginosa

A clinical Pseudomonas aeruginosa isolate resistant to all β-lactams, including ceftolozane-tazobactam and carbapenems, was recovered. It belonged to sequence type 235 and produced the extended-spectrum β-lactamase (ESBL) GES-6 differing from GES-1 by two amino acid substitutions (E104K and G170S). GES-6 possessed an increased hydrolytic activity toward carbapenems and to ceftolozane and a decreased susceptibility to β-lactamase inhibitors compared to GES-1, except for avibactam. We show here that resistance to ceftolozane-tazobactam may occur through acquisition of a specific ESBL in P. aeruginosa but that ceftazidime-avibactam combination remains an effective alternative.

Past and Present Perspectives on β-Lactamases

β-Lactamases, the major resistance determinant for β-lactam antibiotics in Gram-negative bacteria, are ancient enzymes whose origins can be traced back millions of years ago. These well-studied enzymes, currently numbering almost 2,800 unique proteins, initially emerged from environmental sources, most likely to protect a producing bacterium from attack by naturally occurring β-lactams. Their ancestors were presumably penicillin-binding proteins that share sequence homology with β-lactamases possessing an active-site serine. Metallo-β-lactamases also exist, with one or two catalytically functional zinc ions. Although penicillinases in Gram-positive bacteria were reported shortly after penicillin was introduced clinically, transmissible β-lactamases that could hydrolyze recently approved cephalosporins, monobactams, and carbapenems later became important in Gram-negative pathogens. Nomenclature is based on one of two major systems. Originally, functional classifications were used, based on substrate and inhibitor profiles. A later scheme classifies β-lactamases according to amino acid sequences, resulting in class A, B, C, and D enzymes. A more recent nomenclature combines the molecular and biochemical classifications into 17 functional groups that describe most β-lactamases. Some of the most problematic enzymes in the clinical community include extended-spectrum β-lactamases (ESBLs) and the serine and metallo-carbapenemases, all of which are at least partially addressed with new β-lactamase inhibitor combinations. New enzyme variants continue to be described, partly because of the ease of obtaining sequence data from whole-genome sequencing studies. Often, these new enzymes are devoid of any phenotypic descriptions, making it more difficult for clinicians and antibiotic researchers to address new challenges that may be posed by unusual β-lactamases.

Rapid identification of carbapenemase-type blaGES and ESBL-type blaGES using multiplex PCR

Guiana extended-spectrum (GES) β-lactamases are emerging in Japan. The GES family can be classified into 2 groups, one with extended-spectrum β-lactamase (ESBL)-like activity, which hydrolyzes penicillins and cephalosporins, and the other with carbapenemase-like activity with an extended spectrum toward carbapenems. This difference is mediated by variations in a specific amino acid in the GES protein: G170 N or G170S substitutions. We developed an amplification refractory mutation system (ARMS) PCR assay that enabled rapid identification of these variant genes without sequencing.

Detection of multidrug-resistant Pseudomonas aeruginosa harboring bla GES-1 and bla GES-11 in Recife, Brazil

INTRODUCTION

Pseudomonas aeruginosa, an important pathogen globally, presents several resistance mechanisms. This study aimed to investigate the presence of bla GES in clinical isolates of Pseudomonas aeruginosa obtained from various clinical specimens from patients admitted to three different hospitals in Recife, Brazil. The Guiana extended spectrum beta-lactamase (GES) enzymes are responsible for conferring broad spectrum resistance to beta-lactam drugs, including the carbapenems.

METHODS

A total of 100 carbapenem-resistant P. aeruginosa isolates underwent polymerase chain reaction (PCR) testing to identify bla GES, bla KPC, bla SPM-1, bla IMP, and bla VIM. Additionally, PCR products positive for bla GES were sequenced. The clonal profiles of these same isolates were then determined by means of enterobacterial repetitive intergenic consensus (ERIC)-PCR analysis.

RESULTS

PCR analysis revealed that four isolates harbored bla GES; DNA sequencing showed that two harbored bla GES-1 and two bla GES-11. Beta-lactamase genes bla SPM-1, bla IMP, bla VIM, and bla KPC were investigated; none of these genes was detected. Automated susceptibility testing methods (Vitek®2, bioMérieux) showed that the bla GES-1-positive isolates were only susceptible to polymyxin B. The patterns obtained with ERIC-PCR methods showed clonal relationship between the two isolates that harbored bla GES-11, whereas different clonal profiles were found in the isolates harboring bla GES-1.

CONCLUSIONS

We detected the presence of bacterial isolates positive for two different variants of the enzyme GES in three different hospitals from Recife, Brazil. These enzymes have a great capacity for dissemination among Gram-negative bacteria and confer broad-spectrum resistance to beta-lactam antibiotics and to the carbapenems.

A Structure-Based Classification of Class A β-Lactamases, a Broadly Diverse Family of Enzymes

For medical biologists, sequencing has become a commonplace technique to support diagnosis. Rapid changes in this field have led to the generation of large amounts of data, which are not always correctly listed in databases. This is particularly true for data concerning class A β-lactamases, a group of key antibiotic resistance enzymes produced by bacteria. Many genomes have been reported to contain putative β-lactamase genes, which can be compared with representative types. We analyzed several hundred amino acid sequences of class A β-lactamase enzymes for phylogenic relationships, the presence of specific residues, and cluster patterns. A clear distinction was first made between dd-peptidases and class A enzymes based on a small number of residues (S70, K73, P107, 130SDN132, G144, E166, 234K/R, 235T/S, and 236G [Ambler numbering]). Other residues clearly separated two main branches, which we named subclasses A1 and A2. Various clusters were identified on the major branch (subclass A1) on the basis of signature residues associated with catalytic properties (e.g., limited-spectrum β-lactamases, extended-spectrum β-lactamases, and carbapenemases). For subclass A2 enzymes (e.g., CfxA, CIA-1, CME-1, PER-1, and VEB-1), 43 conserved residues were characterized, and several significant insertions were detected. This diversity in the amino acid sequences of β-lactamases must be taken into account to ensure that new enzymes are accurately identified. However, with the exception of PER types, this diversity is poorly represented in existing X-ray crystallographic data.

Structural and Functional Aspects of Class A Carbapenemases

The fight against infectious diseases is probably one of the greatest public health challenges faced by our society, especially with the emergence of carbapenem-resistant gram-negatives that are in some cases pan-drug resistant. Currently,β-lactamase-mediated resistance does not spare even the newest and most powerful β-lactams (carbapenems), whose activity is challenged by carbapenemases. The worldwide dissemination of carbapenemases in gram-negative organisms threatens to take medicine back into the pre-antibiotic era since the mortality associated with infections caused by these "superbugs" is very high, due to limited treatment options. Clinically-relevant carbapenemases belong either to metallo-β- lactamases (MBLs) of Ambler class B or to serine-β-lactamases (SBLs) of Ambler class A and D enzymes. Class A carbapenemases may be chromosomally-encoded (SME, NmcA, SFC-1, BIC-1, PenA, FPH-1, SHV-38), plasmid-encoded (KPC, GES, FRI-1) or both (IMI). The plasmid-encoded enzymes are often associated with mobile elements responsible for their mobilization. These enzymes, even though weakly related in terms of sequence identities, share structural features and a common mechanism of action. They variably hydrolyse penicillins, cephalosporins, monobactams, carbapenems, and are inhibited by clavulanate and tazobactam. Three-dimensional structures of class A carbapenemases, in the apo form or in complex with substrates/inhibitors, together with site-directed mutagenesis studies, provide essential input for identifying the structural factors and subtle conformational changes that influence the hydrolytic profile and inhibition of these enzymes. Overall, these data represent the building blocks for understanding the structure-function relationships that define the phenotypes of class A carbapenemases and can guide the design of new molecules of therapeutic interest.

Nosocomial dissemination of VIM-2-producing ST235 Pseudomonas aeruginosa in Lithuania

Pseudomonas aeruginosa multidrug resistance, and particularly the production of carbapenemases linked to international high-risk clones, is of growing concern. While high levels of carbapenem resistance (>60 %) have been reported in Lithuania, so far, there is no information on the underlying mechanisms. Thus, the aim of this work was to determine the molecular epidemiology and prevalence of acquired carbapenemases among 73 carbapenem-resistant P. aeruginosa isolates recovered in a hospital from Kaunas, Lithuania in 2011-2012. The presence of acquired carbapenemases was evaluated through phenotypic (modified Hodge test, cloxacillin inhibition test, double-disc synergy test) and genetic methods [polymerase chain reaction (PCR) and sequencing]. Clonal relatedness was assessed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Acquired β-lactamases were detected in 19 (26 %) of the isolates, whereas resistance was exclusively chromosomal (OprD inactivation ± AmpC hyperproduction) in the remaining 54 (74 %) isolates. The acquired β-lactamases detected included 16 VIM-2, one PER-1 and two GES enzymes. PFGE revealed that 15 of the 16 VIM-2 isolates belonged to a single clone, identified as the international high-risk clone ST235 by MLST. bla VIM-2 was preceded by aacA7 in a class I integron, similar to epidemic ST235 isolates described in nearby countries. Additionally, sequencing of bla GES revealed the presence of the carbapenem-hydrolysing enzyme GES-5 in one of the isolates and a novel GES variant, designated GES-27, in the other. GES-27 differed from GES-5 by a single amino acid substitution, proline 167, that was replaced by glutamine. Increasing emergence and dissemination of concerning resistance mechanisms and international clones warrants global surveillance and control strategies.