Molecular epidemiology of Enterobacteriaceae isolates producing extended-spectrum beta-lactamases in a French hospital

Population genomics uncovers global distribution, antimicrobial resistance, and virulence genes of the opportunistic pathogen Klebsiella aerogenes

Klebsiella aerogenes is an understudied and clinically important pathogen. We therefore investigate its population structure by genome analysis aligned with metadata. We sequence 130 non-duplicated K. aerogenes clinical isolates and identify two inter-patient transmission events. We then retrieve all publicly available K. aerogenes genomes (n = 1,026, accessed by January 1, 2023) and analyze them with our 130 genomes. We develop a core-genome multi-locus sequence-typing scheme. We find that K. aerogenes is a species complex comprising four phylogroups undergoing evolutionary divergence, likely forming three species. We delineate remarkable clonal diversity and identify three worldwide-distributed carbapenemase-encoding clonal clusters, representing high-risk lineages. We uncover that K. aerogenes has an open genome equipped by a large arsenal of antimicrobial resistance genes. We identify two genetic regions specific for K. aerogenes, encoding a type VI secretion system and flagella/chemotaxis for motility, respectively, both contributing to the virulence. These results provide much-needed insights into the population structure and pan-genomes of K. aerogenes.

In silico and biological activity evaluation of quercetin-boron hybrid compounds, anti-quorum sensing effect as alternative potential against microbial resistance

Boronic acid compounds and the natural flavonoid compound quercetin were handled to synthesize two novel ligands encoded as B1(2,2'-(1,4-phenylenebis (benzo [1,3,2] dioxaborole-2,5-diyl)) bis (3,5,7-trihydroxy-4H- chromen-4-one) and B2(3.3.6. 3,5,7-trihydroxy-2-(2-(6-methoxypyridin-3-yl)benzo[d][1,3,2]dioxaborol-5-yl)- 4 H-chromene-4). Antioxidant activities of ligands were investigated by DPPH, ABTS and CUPRAC methods. Cholinesterase inhibition effects of ligands were determined by acetylcholinesterase and butyrylcholinesterase enzyme inhibition methods, cytotoxic effects of ligands were applied to healthy breast and colon cancer cell lines by MTT method, and urease and tyrosinase enzyme activities were determined. Antimicrobial properties of the compounds were analyzed by detecting their anti-QS potentials on Chromobacterium violaceum biosensor strain. Both compounds were found to have significant antioxidant effects compared to controls. It was determined that the compound B1 at 1-10 µg/mL was more active than the reference compounds (α-TOC and BHT). Moreover, the enzyme activity studies on ligands demonstrated that acetylchoinesterase and butyrylcholinesterase enzyme inhibitions were higher than the reference compounds. As expected, boron derivatives exhibited respectable activity against the biofilms of Escherichia coli (E. coli) and P. aeruginosa (P. aeruginosa). These results demonstrate the potential applicability of boron derivatives in the treatment of biofilm-associated infections and provide a practical strategy for the design of new boron-based antimicrobial materials. In silico molecular docking studies were performed on ligands to identify newly synthesized compounds. The binding parameter values and binding sites of the compounds were also determined. In conclusion, our studies showed that newly synthesized hybrid compounds could be solutions for antimicrobial resistance and enzyme-related disorders.

Epidemiology and mechanisms of tigecycline- and carbapenem- resistant Enterobacter cloacae in Southwest China: a five-year retrospective study

BACKGROUND

The prevalence and molecular epidemiology of tigecycline resistance in carbapenem-resistant Enterobacter cloacae (CREC) in mainland China is unknown. In this study, we aimed to investigate the molecular characteristics and resistance mechanism of tigecycline-resistant CREC (TCREC) in Southwest China.

METHODS

We conducted a five-year retrospective study. TCREC isolates were subjected to antimicrobial susceptibility testing, pulsed-field gel electrophoresis, and multilocus sequence typing. We determined the presence of genes, deficiency of outer membrane proteins, and expression of efflux pumps using polymerase chain reaction (PCR), reverse transcription-polymerase chain reaction (RT-PCR), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

We found that a high incidence rate of 21.7% (36/166) of isolates were positive for TCREC. All isolates were resistant to ertapenem whereas 67% remained susceptible to imipenem and meropenem. ST88 (10/36, 27.8%) was predominant and associated with moderate resistance to tigecycline and high resistance to carbapenems, followed by ST256 (3/36, 8.3%), ST78 (2/36, 5.6%), ST577 (2/36, 5.6%), and ST102 (2/36, 5.6%). bla_NDM-1 (6/36, 16.6%) carriers was the most common carbapenemase gene and ST88 (5/6, 83.3%) was the most common type, followed by bla_IMP-8 (n=3/36, 8.3%). Coexistence of extensive-spectrum β-lactamase (ESBL) genes and outer membrane protein OmpF and/or OmpC loss were found in 27 out of 36 isolates, in addition, increased co-expression of efflux pump genes acrB and oqxA was identified in 25 out of 36 isolates, which may together contribute to co-resistance to carbapenem and tigecycline.

CONCLUSION

Most ST88 strains carried carbapenemases, especially New Delhi metallo-β-lactamase 1 (NDM-1). Overexpression of efflux pumps contributed to tigecycline resistance. The presence of carbapenemase and/or ESBL genes and lack of outer membrane proteins, but not overexpression of efflux pumps, may confer carbapenem resistance. Reasonable supervision and management the epidemic of TCREC will help to stem the transmission of the isolates.

Enterobacter spp.: Update on Taxonomy, Clinical Aspects, and Emerging Antimicrobial Resistance

The genus Enterobacter is a member of the ESKAPE group, which contains the major resistant bacterial pathogens. First described in 1960, this group member has proven to be more complex as a result of the exponential evolution of phenotypic and genotypic methods. Today, 22 species belong to the Enterobacter genus. These species are described in the environment and have been reported as opportunistic pathogens in plants, animals, and humans. The pathogenicity/virulence of this bacterium remains rather unclear due to the limited amount of work performed to date in this field. In contrast, its resistance against antibacterial agents has been extensively studied. In the face of antibiotic treatment, it is able to manage different mechanisms of resistance via various local and global regulator genes and the modulation of the expression of different proteins, including enzymes (β-lactamases, etc.) or membrane transporters, such as porins and efflux pumps. During various hospital outbreaks, the Enterobacter aerogenes and E. cloacae complex exhibited a multidrug-resistant phenotype, which has stimulated questions about the role of cascade regulation in the emergence of these well-adapted clones.

Draft Genome Sequences of Two Enterobacter cloacae subsp. cloacae Strains Isolated from Australian Hematology Patients with Bacteremia

Enterobacter cloacae is a common member of the gut microbiota in healthy individuals. However, it is also an opportunistic pathogen, capable of causing bacteremia. We report the draft genomes of two Enterobacter cloacae subspecies cloacae strains isolated from hematology patients with bacteremia. Both isolates carry genes encoding extended-spectrum β-lactamases.

Molecular epidemiology of quinolon resistant strains of extended spectrum beta-lactamase producing Escherichia coli

Objective:

To determine the clonal relationship of ESBL-producing and quinolone resistant E.coli strains and to investigate the risk factors for infections with these microorganisms.

Methods:

A total of 95 ESBL-producing and quinolone resistant E.coli strains isolated from various clinical specimens of inpatients and outpatients in our hospital were included in the study. Risk factors for infections with ESBL-producing E.coli and demographic data of the patients were obtained from hospital records. The rep-PCR method was used for the determination of the genetic relationship of the strains.

Results:

Of the strains included in the study, 33(34.7%) were isolated from inpatients and 62(65.3%) from outpatients. At least one risk factor has been identified in all patients for infection with ESBL producing E.coli and the mean of the risk factors of patients was 4.2. The most common risk factor was urinary catheter insertion (57.9%). The distribution of the strains in each clone was as fallows: clone A: 9(9.5%), clone B: 10(10.5%), clone C: 38(40%), clone D: 12(12.5%), clone E: 6(6.3%), clone F: 7(7.3%) and clone G 5(5.3%). The clones A, D and C (dominant clone) were isolated from hospital and community acquired infections. Clones E, F and G were identified as nosocomial clones.

Conclusion:

Infections with multidrug resistant bacteria may be related to the hospital although they were isolated from outpatients. Developing a medical record system is vitally important to prevent the occurence and spread of resistant bacterial infections in the community.

Clinical and Molecular Epidemiology of Extended-Spectrum Beta-Lactamase-Producing Klebsiella spp.: A Systematic Review and Meta-Analyses

Healthcare-related infections caused by extended-spectrum beta-lactamase (ESBL)-producing Klebsiella spp. are of major concern. To control transmission, deep understanding of the transmission mechanisms is needed. This systematic review aimed to identify risk factors and sources, clonal relatedness using molecular techniques, and the most effective control strategies for ESBL-producing Klebsiella spp. A systematic search of PubMed, Embase, and Outbreak Database was performed. We identified 2771 articles from November 25th, 1960 until April 7th, 2014 of which 148 were included in the systematic review and 23 in a random-effects meta-analysis study. The random-effects meta-analyses showed that underlying disease or condition (odds ratio [OR] = 6.25; 95% confidence interval [CI] = 2.85 to 13.66) generated the highest pooled estimate. ESBL-producing Klebsiella spp. were spread through person-to-person contact and via sources in the environment; we identified both monoclonal and polyclonal presence. Multi-faceted interventions are needed to prevent transmission of ESBL-producing Klebsiella spp.

In Vivo Evolution of Bacterial Resistance in Two Cases of Enterobacter aerogenes Infections during Treatment with Imipenem

Infections caused by multidrug resistant (MDR) bacteria are a major concern worldwide. Changes in membrane permeability, including decreased influx and/or increased efflux of antibiotics, are known as key contributors of bacterial MDR. Therefore, it is of critical importance to understand molecular mechanisms that link membrane permeability to MDR in order to design new antimicrobial strategies. In this work, we describe genotype-phenotype correlations in Enterobacter aerogenes, a clinically problematic and antibiotic resistant bacterium. To do this, series of clinical isolates have been periodically collected from two patients during chemotherapy with imipenem. The isolates exhibited different levels of resistance towards multiple classes of antibiotics, consistently with the presence or the absence of porins and efflux pumps. Transport assays were used to characterize membrane permeability defects. Simultaneous genome-wide analysis allowed the identification of putative mutations responsible for MDR. The genome of the imipenem-susceptible isolate G7 was sequenced to closure and used as a reference for comparative genomics. This approach uncovered several loci that were specifically mutated in MDR isolates and whose products are known to control membrane permeability. These were omp35 and omp36, encoding the two major porins; rob, encoding a global AraC-type transcriptional activator; cpxA, phoQ and pmrB, encoding sensor kinases of the CpxRA, PhoPQ and PmrAB two-component regulatory systems, respectively. This report provides a comprehensive analysis of membrane alterations relative to mutational steps in the evolution of MDR of a recognized nosocomial pathogen.

An adaptive response of Enterobacter aerogenes to imipenem: regulation of porin balance in clinical isolates

Imipenem (IPM) is a carbapenem antibiotic frequently used in severe hospital infections. Several reports have mentioned the emergence of resistant isolates exhibiting membrane modifications. A study was conducted between September 2005 and August 2007 to survey infections due to Enterobacter aerogenes in patients hospitalised in a French university hospital. Resistant E. aerogenes clinical isolates obtained from patients treated with IPM and collected during the 3 months following initiation of treatment were phenotypically and molecularly characterised for β-lactamases, efflux pumps activity and outer membrane proteins. Among the 339 patients infected with E. aerogenes during the study period, 41 isolates (12.1%) were resistant to extended-spectrum cephalosporins and 17 patients (5.0%) were treated with IPM. The isolates from these 17 patients presented TEM-24 and basal efflux expression. Following IPM treatment, an IPM-intermediate-susceptible (IPM-I) isolate emerged in 11 patients and an IPM-resistant (IPM-R) isolate in 6 patients. A change in the porin balance (Omp35/Omp36) was observed in IPM-I isolates exhibiting ertapenem resistance. Finally, a porin deficiency (Omp35 and Omp36 absence) was detected in IPM-R isolates associated with efflux pump expression. This study indicates that the alteration in porin expression, including the shift of porin expression and lack of porins, contribute to the E. aerogenes adaptive response to IPM treatment.

Extended-spectrum beta-lactamase-producing Klebsiella pneumoniae infection in a neonatal intensive care unit

BACKGROUND

A molecular epidemiological survey was conducted on an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBLKp) infection in our neonatal intensive care unit (NICU) from February to June 2008.

METHODS

Cultures of clinical samples from neonates in the NICU, the hands of healthcare workers and the environment of the NICU were subjected to ESBLKp isolation. Pulsed-field gel electrophoresis was performed to determine Klebsiella pneumoniae strains (type A-D).

RESULTS

In 1439 neonates, 38 (2.6%) had infections and 65 (4.5%) had colonizations with ESBLKp. Microbiological sampling of the NICU environment yielded 33 (14.9%) ESBLKp isolates from 222 samples. Clone A was found in 88.2% of the infected neonates, 66.7% of the colonized neonates, 69.7% of the environmental samples, and the hands of a healthcare worker.

CONCLUSIONS

The detection rate of ESBLKp is high in environmental samples, especially those from frequently touched surfaces. Since ESBLKp was identified on the hands of a healthcare worker in the present study, hand and environmental hygiene is mandatory for infection control in neonatal intensive care units.

Virulence potential of Escherichia coli strains causing asymptomatic bacteriuria during pregnancy

We compared the virulence properties of a collection of asymptomatic bacteriuria (ABU) Escherichia coli strains to urinary tract infection (UTI) strains isolated from pregnant women in a university hospital over 1 year. The in vitro and in vivo studies suggest that ABU strains presented a virulence behavior similar to that of strains isolated from cases of cystitis.

Membrane permeability, a pivotal function involved in antibiotic resistance and virulence in Enterobacter aerogenes clinical isolates

Imipenem-susceptible E. aerogenes isolates exhibiting extended spectrum β-lactamases, target mutations and a basal efflux expression, were identified in five patients. After imipenem treatment, imipenem-intermediate susceptible (IMI-I) or resistant (IMI-R) isolates emerged in these patients. Alteration in porin synthesis and increase in efflux expression were observed in the IMI-I isolates whereas complete loss of the porins, LPS alteration and efflux overexpression were observed in the IMI-R isolates. Bacterial virulence of the strains was investigated by the Caenorhabditis elegans model. The IMI-R isolates were shown to be significantly less virulent than the IMI-susceptible or IMI-I isolates. The pleiotropic membrane alteration and its associated fitness burden exhibited by E. aerogenes isolates influence their antibiotic resistance and their virulence behaviour. These findings highlight the balance between the low permeability-related resistance and virulence and their relationships with the treatment of resistant pathogens.

Implication of porins in beta-lactam resistance of Providencia stuartii

An integrative approach combining biophysical and microbiological methods was used to characterize the antibiotic translocation through the outer membrane of Providencia stuartii. Two novel members of the General Bacterial Porin family of Enterobacteriaceae, named OmpPst1 and OmpPst2, were identified in P. stuartii. In the presence of ertapenem (ERT), cefepime (FEP), and cefoxitin (FOX) in growth media, several resistant derivatives of P. stuartii ATCC 29914 showed OmpPst1-deficiency. These porin-deficient strains showed significant decrease of susceptibility to β-lactam antibiotics. OmpPst1 and OmpPst2 were purified to homogeneity and reconstituted into planar lipid bilayers to study their biophysical characteristics and their interactions with β-lactam molecules. Determination of β-lactam translocation through OmpPst1 and OmpPst2 indicated that the strength of interaction decreased in the order of ertapenem ≫ cefepime > cefoxitin. Moreover, the translocation of these antibiotics through OmpPst1 was more efficient than through OmpPst2. Heterologous expression of OmpPst1 in the porin-deficient E. coli strain BL21(DE3)omp8 was associated with a higher antibiotic susceptibility of the E. coli cells to β-lactams compared with expression of OmpPst2. All our data enlighten the involvement of porins in the resistance of P. stuartii to β-lactam antibiotics.

Nationwide survey of extended-spectrum {beta}-lactamase-producing Enterobacteriaceae in the French community setting

OBJECTIVES

The aim of this study was to assess the prevalence of the extended-spectrum beta-lactamase (ESBL)-producing enterobacteria (ESBLE) in the French community, during a 2006 survey.

METHODS

All enterobacteria isolated from urine samples of patients, exhibiting a decreased susceptibility to broad-spectrum cephalosporins, were analysed for their beta-lactamase content (synergy test, isoelectrofocusing, conjugation transfer, PCR amplification and/or cloning experiments and sequencing). Additional co-resistances were investigated by PCR, sequencing and/or cloning. Epidemiological relationship was studied by PFGE for all species and, in addition, for Escherichia coli by the determination of the phylogenetic group, multilocus sequence type (ST) and O25b antigen. Characteristics of CTX-M-producing E. coli carriers were compared with other ESBLE carriers.

RESULTS

Seventy-two ESBLE were collected from 71 patients. Most of them expressed a CTX-M enzyme (n = 42, comprising 40 E. coli), with a predominance of CTX-M-15 (n = 24); 10 CTX-M-15-producing E. coli belonged to the same clone (phylogroup B2, ST131, serotype O25b). The 30 remaining strains possessed a TEM- or SHV-type ESBL. In addition, three strains presented unusual co-resistances such as DHA-1 (n = 2), QnrB4 and ArmA. Risk factors for ESBLE acquisition were substantially less frequent when the ESBL was of the CTX-M type, except for prior antimicrobial therapy. Eighteen percent of the patients were considered to have true community-acquired ESBLE; most of them harboured a CTX-M-producing E. coli.

CONCLUSIONS

This first nationwide study reports an ESBLE prevalence of 1.1% in the French community setting in 2006, mainly related to the presence of CTX-M-producing E. coli strains; furthermore, unusual co-resistances rarely found in the community setting were occasionally observed, which may threaten future emergence.

Occurrence of efflux mechanism and cephalosporinase variant in a population of Enterobacter aerogenes and Klebsiella pneumoniae isolates producing extended-spectrum beta-lactamases

We investigated the occurrence of multidrug resistance in 44 Enterobacter aerogenes and Klebsiella pneumoniae clinical isolates. Efflux was involved in resistance in E. aerogenes isolates more frequently than in K. pneumoniae isolates (100 versus 38% of isolates) and was associated with the expression of phenylalanine arginine beta-naphthylamide-susceptible active efflux. AcrA-TolC overproduction in E. aerogenes isolates was noted. An analysis of four E. aerogenes isolates for which cefepime MICs were high revealed no modification in porin expression but a new specific mutation in the AmpC beta-lactamase.

Evidence for recombination among the alleles encoding TEM and SHV beta-lactamases

OBJECTIVES

The objective of this research was to determine whether recombination occurs in class A beta-lactamases.

METHODS

We performed chi(2) analysis of the observed and expected numbers of times that beta-lactamases from the TEM, SHV and CTX-M groups co-occurred. Additionally, we performed phylogenetic analysis to detect independent occurrences of silent mutations in bla(TEM) and bla(SHV) variants.

RESULTS

We found that the distribution of co-occurring bla(TEM), bla(SHV) and bla(CTX-M) alleles in clinical microbial populations is consistent with the regular occurrence of recombination among alleles within the groups. We also found that the distribution of silent mutations in bla(TEM) and bla(SHV) alleles is inconsistent with spontaneous point mutations.

CONCLUSIONS

Our findings indicate that recombination has an important effect on the sequence evolution and population distribution of the alleles that encode class A beta-lactamases.

Identification and evolution of drug efflux pump in clinical Enterobacter aerogenes strains isolated in 1995 and 2003

Background

The high mortality impact of infectious diseases will increase due to accelerated evolution of antibiotic resistance in important human pathogens. Development of antibiotic resistance is a evolutionary process inducing the erosion of the effectiveness of our arsenal of antibiotics. Resistance is not necessarily limited to a single class of antibacterial agents but may affect many unrelated compounds; this is termed ‘multidrug resistance’ (MDR). The major mechanism of MDR is the active expulsion of drugs by bacterial pumps; the treatment of Gram negative bacterial infections is compromised due to resistance mechanisms including the expression of efflux pumps that actively expel various usual antibiotics (ß-lactams, quinolones, …).

Methodology/Principal Findings

Enterobacter aerogenes has emerged among Enterobacteriaceae associated hospital infections during the last twenty years due to its faculty of adaptation to antibiotic stresses. Clinical isolates of E. aerogenes belonging to two strain collections isolated in 1995 and 2003 respectively, were screened to assess the involvement of efflux pumps in antibiotic resistance. Drug susceptibility assays were performed on all bacterial isolates and an efflux pump inhibitor (PAßN) previously characterized allowed to decipher the role of efflux in the resistance. Accumulation of labelled chloramphenicol was monitored in the presence of an energy poison to determine the involvement of active efflux on the antibiotic intracellular concentrations. The presence of the PAßN-susceptible efflux system was also identified in resistant E. aerogenes strains.

Conclusions/Significance

For the first time a noticeable increase in clinical isolates containing an efflux mechanism susceptible to pump inhibitor is report within an 8 year period. After the emergence of extended spectrum ß-lactamases in E. aerogenes and the recent characterisation of porin mutations in clinical isolates, this study describing an increase in inhibitor-susceptible efflux throws light on a new step in the evolution of mechanism in E. aerogenes.

Virulence genotype and nematode-killing properties of extra-intestinal Escherichia coli producing CTX-M beta-lactamases

This study evaluated the virulence potential of Escherichia coli isolates producing CTX-M beta-lactamases. During a 24-month period, 33 extended-spectrum beta-lactamase (ESBL)-producing E. coli, including 14 CTX-M-producers, were isolated from urinary tract infections at Nîmes University Hospital, France. The prevalence of 14 major virulence factors (VFs) was investigated by PCR and compared with the prevalence in a group of 99 susceptible E. coli isolates. Ten VFs were less prevalent (p <0.05) in the ESBL isolates than the susceptible E. coli, while iutA and traT were more prevalent in ESBL isolates (p <0.05). Moreover, the CTX-M-producing isolates had significantly fewer VFs than TEM-producing isolates. A novel infection model using the nematode Caenorhabditis elegans was developed to assess the virulence properties of extra-intestinal pathogenic E. coli (ExPEC) strains in vivo. C. elegans infection assays, using 14 ESBL-producing E. coli and ten susceptible E. coli isolates, indicated that the ability to kill nematodes correlated with the presence of VFs, and that CTX-M-producing isolates had relatively low virulence in vivo. Overall, the results suggested that hospital-acquired CTX-M-producing E. coli, although adapted for survival in an antibiotic-rich environment such as the hospital milieu, have a relatively low intrinsic virulence potential.

Recombination and selection can remove blaTEM alleles from bacterial populations

We passaged cells expressing TEM-1 and TEM-12 from a single plasmid through either ampicillin or ceftazidime. We found that the combined effects of recombination and selection removed the bla(TEM-1) allele from the bacterial population when it was passaged through ceftazidime or the bla(TEM-12) allele when cultures were passaged through ampicillin.

Fitness trade-offs in blaTEM evolution

bla(TEM-1) expression results in penicillin resistance, whereas expression of many bla(TEM-1) descendants, called extended-spectrum beta-lactamases (ESBLs), results simultaneously in resistance to penicillins and extended-spectrum cephalosporins. Despite the expanded resistance phenotypes conferred by many ESBLs, bla(TEM-1) is still the most abundant bla(TEM) allele in many microbial populations. This study examines the fitness effects of the two amino acid substitutions, R164S and E240K, that have occurred repeatedly among ESBL bla(TEM-1) descendants. Using a single-nucleotide polymorphism-specific real-time quantitative PCR method, we analyzed the fitness of strains expressing bla(TEM-1), bla(TEM-10), and bla(TEM-12). Our results show that bacteria expressing the ancestral bla(TEM-1) allele have a fitness advantage over those expressing either bla(TEM-10) or bla(TEM-12) when exposed to ampicillin. This observation, combined with the fact that penicillins are the most prevalent antimicrobials prescribed worldwide, may explain why bla(TEM-1) has persisted as the most frequently encountered bla(TEM) allele in bacterial populations.

Prevalence and spread of extended-spectrum beta-lactamase-producing Enterobacteriaceae in Europe

Extended-spectrum beta-lactamases (ESBLs) represent a major threat among resistant bacterial isolates. The first types described were derivatives of the TEM-1, TEM-2 and SHV-1 enzymes during the 1980s in Europe, mainly in Klebsiella pneumoniae associated with nosocomial outbreaks. Nowadays, they are mostly found among Escherichia coli isolates in community-acquired infections, with an increasing occurrence of CTX-M enzymes. The prevalence of ESBLs in Europe is higher than in the USA but lower than in Asia and South America. However, important differences among European countries have been observed. Spread of mobile genetic elements, mainly epidemic plasmids, and the dispersion of specific clones have been responsible for the increase in ESBL-producing isolates, such as those with TEM-4, TEM-24, TEM-52, SHV-12, CTX-M-9, CTX-M-14, CTX-M-3, CTX-M-15 and CTX-M-32 enzymes.

Nationwide study of the prevalence, characteristics, and molecular epidemiology of extended-spectrum-beta-lactamase-producing Enterobacteriaceae in France

Among 10,872 isolates of Enterobacteriaceae from a nationwide study of 88 French hospitals in 2005, 169 (1.7%) expressed an extended-spectrum beta-lactamase. The most prevalent species were Escherichia coli (48.5%), Enterobacter aerogenes (23.7%), and Klebsiella pneumoniae (14.8%). Molecular analysis underlined the polyclonal spread of CTX-M-expressing E. coli, primarily isolates of the CTX-M-1 subgroup.

An early response to environmental stress involves regulation of OmpX and OmpF, two enterobacterial outer membrane pore-forming proteins

Bacterial adaptation to external stresses and toxic compounds is a key step in the emergence of multidrug-resistant strains that are a serious threat to human health. Although some of the proteins and regulators involved in antibiotic resistance mechanisms have been described, no information is available to date concerning the early bacterial response to external stresses. Here we report that the expression of ompX, encoding an outer membrane protein, is increased during early exposure to drugs or environmental stresses. At the same time, the level of ompF porin expression is noticeably affected. Because of the role of these proteins in membrane permeability, these data suggest that OmpF and OmpX are involved in the control of the penetration of antibiotics such as beta-lactams and fluoroquinolones through the enterobacterial outer membrane. Consequently, the early control of ompX and ompF induced by external stresses may represent a preliminary response to antibiotics, thus triggering the initial bacterial line of defense against antibiotherapy.

Extended-spectrum-beta-lactamase-producing Enterobacteriaceae strains in various types of private health care centers

During a 2004 survey, 49 extended-spectrum-beta-lactamase-producing enterobacteria were collected in 20 French private health care centers and one local hospital. They included 12 CTX-M-producing Escherichia coli strains (1.8% versus 0.3% in a 1999 survey). Most of them belonged to the same clone and contained a bla(CTX-M-15) gene on similar conjugative plasmids.

Nosocomial outbreak due to extended-spectrum-beta-lactamase- producing Enterobacter cloacae in a cardiothoracic intensive care unit

Enterobacter cloacae has been associated with several outbreaks, usually involving strains that overproduce chromosomal beta-lactamase or, uncommonly, strains expressing extended-spectrum beta-lactamases (ESBL). Only sporadic cases of ESBL-producing E. cloacae have been identified in our hospital in recent years. We describe the epidemiology and clinical and microbiological characteristics of an outbreak caused by ESBL-producing E. cloacae in a cardiothoracic intensive care unit (CT-ICU). Prospective surveillance of patients with infection or colonization by ESBL-producing E. cloacae among patients admitted to the CT-ICU was performed during the outbreak. Production of ESBL was determined by decreased susceptibility to expanded-spectrum cephalosporins and a positive double-disk test result. Clone relatedness was determined by pulsed-field gel electrophoresis (PFGE). From July to September 2005, seven patients in the CT-ICU with ESBL-producing E. cloacae were identified (four males; median age, 73 years; range, 45 to 76 years); six patients had cardiac surgery. Four patients developed infections; three had primary bacteremia, one had ventilator-associated pneumonia, and one had tracheobronchitis. ESBL-producing E. cloacae showed resistance to quinolones and aminoglycosides. PFGE revealed two patterns. Five isolates belonged to clone A; two carried a single ESBL (pI 8.2 and a positive PCR result for the SHV type), and three carried two ESBLs (pIs 8.1 and 8.2 and positive PCR results for the SHV and CTX-M-9 types). Isolates belonging to clone B carried a single ESBL (pI 5.4 and a positive PCR result for the TEM type). Review of antibiotic consumption showed increased use of cefepime and quinolones during June and July 2005. The outbreak was stopped by the implementation of barrier measures and cephalosporin restriction. ESBL production could be increasingly common in nosocomial pathogens other than Escherichia coli or Klebsiella pneumoniae.

Dissemination and persistence of a plasmid-mediated TEM-3-like beta-lactamase, TEM-139, among Enterobacteriaceae in Bulgaria

During a survey of extended-spectrum beta-lactamases (ESBLs) in Bulgaria from 1996 to 2003, a TEM-3-like ESBL was detected in strains of Klebsiella pneumoniae, Escherichia coli, Citrobacter freundii and Klebsiella oxytoca from three centres in three different towns. The nucleotide sequence of the cloned gene was identical to that of TEM-3, except for one substitution (C347A) causing an amino acid exchange at position 49 from leucine to methionine. This TEM-3 variant with both a unique nucleotide and amino acid sequence was designated TEM-139. Transformants producing TEM-3 or TEM-139 expressed identical beta-lactam resistance phenotypes. TEM-139 was the only TEM-type ESBL detected in the surveyed hospitals (seven centres in three towns). TEM-139 is a natural variant of TEM-3 with an amino acid exchange without informational content, detectable only by molecular procedures, e.g. a nucleotide-specific polymerase chain reaction.

CTX-M beta-lactamase-producing Escherichia coli in French hospitals: prevalence, molecular epidemiology, and risk factors

In 2004, 65 CTX-M-producing Escherichia coli isolates were collected from infected patients in four French hospitals. The blaCTX-M-15 genes were predominant. Pulsed-field gel electrophoresis highlighted a clonal propagation of CTX-M-15-producing strains belonging to phylogenetic group B2, notably in the community. The main risk factors for acquiring these isolates were urinary tract infections or the presence of a urinary catheter in diabetic or renal failure patients.

Caenorhabditis elegans : modèle d'étude in vivo de la virulence bactérienne

The nematode Caenorhabditis elegans presents many advantages as a model system. The worm has recently emerged as a potentially useful tool for the study of host-pathogen interactions. This paper presents advantages and inconveniences of this model, the variety of bacterial pathogens studied, and its use to monitor virulence of Extraintestinal Escherichia coli strains.

qnrA in CTX-M-producing Escherichia coli isolates from France

By PCR, we screened for qnr genes 112 clinical isolates of extended-spectrum beta-lactamase-producing Escherichia coli collected from hospitals in France during 2004. For the first time, 7.7% of CTX-M-producing E. coli isolates presented a plasmid-mediated resistance to quinolones. All strains harbored a qnrA gene located on a sul1-type class 1 integron with similar structure to the In36 integron.

Spread of novel expanded-spectrum β-lactamases in Enterobacteriaceae in a university hospital in the Paris area, France

In 2002, 28 non-duplicate enterobacterial isolates producing extended-spectrum beta-lactamases (ESBLs) were collected from infected patients at the Bicêtre Hospital in Paris, France. Escherichia coli was the predominant ESBL-positive enterobacterial species, comprising ten (36%) of the isolates. CTX-M enzymes (CTX-M-3, CTX-M-10, CTX-M-14 and CTX-M-15) were produced by 11 (39%) of the isolates (six E. coli, two Enterobacter cloacae, one Enterobacter aerogenes, one Proteus mirabilis and one Citrobacter freundii). Other ESBLs, such as VEB-1 and PER-1, were also detected, but less frequently.

Successive emergence of Enterobacter aerogenes strains resistant to imipenem and colistin in a patient

Enterobacter aerogenes is an agent of hospital-acquired infection that exhibits a remarkable resistance to beta-lactam antibiotics during therapy. Five successive isolates of E. aerogenes infecting a patient and exhibiting a multiresistance phenotype to beta-lactam antibiotics and fluoroquinolones were investigated. Among these clinical strains, four presented resistant phenotypes during successive imipenem and colistin treatments. The involved resistance mechanisms exhibited by the successive isolates were associated with alterations of the outer membrane that caused a porin decrease and lipopolysaccharide modifications.