Detection and characterization of Enterobacteriaceae producing metallo-β-lactamases in a tertiary-care hospital in Spain

Genomically-supported Redefinition of an Outbreak in a Pediatric Unit Caused by blaVIM -harboring Klebsiella michiganensis

BACKGROUND

Klebsiella michiganensis , a member of the Klebsiella oxytoca complex, is an emerging nosocomial pathogen known to frequently carry plasmids with antibiotic-resistance genes, including carbapenemases. Using genomics, this study redefined an outbreak alert of K. michiganensis carrying a blaVIM carbapenemase in a pediatric ward in a Spanish hospital.

METHODS

A total of 31 isolates of Verona integron-encoded metallo-β-lactamase (VIM)-carbapenemase K. oxytoca from suspected outbreak cases and unrelated controls from 2015 to 2022 were analyzed. Whole-genome sequencing (both short and long reads) was applied to determine phylogenetic relationships based on single-nucleotide polymorphisms (SNPs) and identify plasmids and antimicrobial resistance genes.

RESULTS

The sequences from 12 isolates identified in 2021 showed pairwise SNP distances ranging from 0 to 16 SNPs, confirming the outbreak. Examination of isolates before and after the study period revealed 7 additional cases, 2 in 2020 and 5 in 2022. The outbreak comprised 18 isolates from 17 patients in 3 different pediatric wards, together with 1 environmental sample. In all outbreak isolates, the blaVIM-1 gene was located within a gene cassette carried by a class 1 integron on an IncFIB(pQil) plasmid. A genomic network based on SNPs revealed 5 unsampled intermediate nodes, suggesting additional subclones that may have involved healthcare staff, patient relatives or environmental reservoirs. Blood and rectal isolates obtained from the same patient were positioned on separate branches of the network, making a direct evolutionary pathway between them unlikely.

CONCLUSIONS

Our study redefined the full extent of this K. michiganensis -VIM outbreak and highlights the critical importance of genomic analysis in accurately understanding outbreaks in healthcare settings.

Xenogenetic evolutionary of integrons promotes the environmental pollution of antibiotic resistance genes - Challenges, progress and prospects

Environmental pollution of antibiotic resistance genes (ARGs) has been a great public concern. Integrons, as mobile genetic elements, with versatile gene acquisition systems facilitate the horizontal gene transfer (HGT) and pollution disseminations of ARGs. However, little is understood about the characteristics of ARGs mediated by integrons, which hampers our monitoring and control of the mobile antimicrobial resistance risks. To address these issues, we reviewed 3,322 publications concerning detection methods and pipeline, ARG diversity and evolutionary progress, environmental and geographical distribution, bacterial hosts, gene cassettes arrangements, and based on which to identify ARGs with high risk levels mediated by integrons. Diverse ARGs of 516 subtypes attributed to 12 types were capable of being carried by integrons, with 62 core ARG subtypes prevalent in pollution source, natural and human-related environments. Hosts of ARG-carrying integrons reached 271 bacterial species, most frequently carried by opportunistic pathogens Escherichia coli, Pseudomonas aeruginosa and Klebsiella pneumoniae. Moreover, the observed emergence of ARGs together with their multiple arrangements indicated the accumulation of ARGs mediated by integrons, and thus pose increasing HGT risks under modern selective agents. With the concerns of public health, we urgently call for a better monitoring and control of these high-risk ARGs. Our identified Risk Rank I ARGs (aacA7, blaOXA10, catB3, catB8, dfrA5) with high mobility, reviewed key trends and noteworthy advancements, and proposed future directions could be reference and guidance for standard formulation.

Klebsiella oxytoca Complex: Update on Taxonomy, Antimicrobial Resistance, and Virulence

Klebsiella oxytoca is actually a complex of nine species-Klebsiella grimontii, Klebsiella huaxiensis, Klebsiella michiganensis, K. oxytoca, Klebsiella pasteurii, Klebsiella spallanzanii, and three unnamed novel species. Phenotypic tests can assign isolates to the complex, but precise species identification requires genome-based analysis. The K. oxytoca complex is a human commensal but also an opportunistic pathogen causing various infections, such as antibiotic-associated hemorrhagic colitis (AAHC), urinary tract infection, and bacteremia, and has caused outbreaks. Production of the cytotoxins tilivalline and tilimycin lead to AAHC, while many virulence factors seen in Klebsiella pneumoniae, such as capsular polysaccharides and fimbriae, have been found in the complex; however, their association with pathogenicity remains unclear. Among the 5,724 K. oxytoca clinical isolates in the SENTRY surveillance system, the rates of nonsusceptibility to carbapenems, ceftriaxone, ciprofloxacin, colistin, and tigecycline were 1.8%, 12.5%, 7.1%, 0.8%, and 0.1%, respectively. Resistance to carbapenems is increasing alarmingly. In addition to the intrinsic bla_OXY, many genes encoding β-lactamases with varying spectra of hydrolysis, including extended-spectrum β-lactamases, such as a few CTX-M variants and several TEM and SHV variants, have been found. bla_KPC-2 is the most common carbapenemase gene found in the complex and is mainly seen on IncN or IncF plasmids. Due to the ability to acquire antimicrobial resistance and the carriage of multiple virulence genes, the K. oxytoca complex has the potential to become a major threat to human health.

Characterization of the IncFII-IncFIB(pB171) Plasmid Carrying bla NDM-5 in Escherichia coli ST405 Clinical Isolate in Japan

Purpose

New Delhi metallo-β-lactamase 5 (NDM-5) shows stronger resistance to carbapenems and broad-spectrum cephalosporins than NDM-1 because NDM-5 differs from NDM-1 by two amino acid substitutions. In this study, our aim was to characterize a NDM-5-producing Escherichia coli isolate KY1497 from a patient with urinary tract infection in Japan, who had no recent history of overseas travel.

Patients and Methods

NDM-5-producing E. coli isolate KY1497 was detected in the urine sample of a patient hospitalized in a tertiary hospital in Japan. The complete genome sequence of isolate KY1497 was determined by short- and long-read sequencing with hybrid assembly, followed by multilocus sequence typing (MLST), core-genome phylogeny analysis, plasmid analysis, and transconjugation experiments.

Results

KY1497 was classified as ST405 by MLST, and core-genome phylogeny exhibited the closest lineage to the clinical isolates in Nepal (IOMTU605) and Canada (FDAARGOS_448). KY1497 harbors bla_NDM-5 in the IncFII-IncFIB(pB171) replicon plasmid (pKY1497_1, 123,767 base pairs). Plasmid analysis suggested that the cognate plasmids of pKY1497_1 have a minor plasmid background, rather than the globally disseminated IncX3 plasmid carrying bla_NDM-5. Transconjugation analysis revealed that pKY1497_1 is transmissible to the recipient E. coli J53 strain.

Conclusion

We characterized a novel Inc replicon plasmid (IncFII-IncFIB[pB171]) carrying bla_NDM-5 and its host E. coli strain. NDMs are associated with a high risk of infection worldwide because of their antibiotic resistance and untreatable and hard-to-treat infections. Other patients in the hospital showed negative results for carbapenem-resistant Enterobacteriaceae. As NDM-producing strains are only sporadically detected in Japan, attention should be provided to the community prevalence of NDM-producing E. coli strains to prevent nosocomial infections.

Genomic path to pandrug resistance in a clinical isolate of Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae have spread globally throughout tertiary hospitals. Many Carbapenem-resistant K. pneumoniae clinical isolates are multidrug-resistant (MDR) and may become eventually pandrug-resistant (PDR). Here we present the closed genome of a PDR VIM-1-producing K. pneumoniae strain (KP1050) obtained in a tertiary hospital. The isolate belonged to sequence type 54 (ST54) and had five extrachromosomal elements (four plasmids and a circular phage genome). Most of the antimicrobial resistance genes (ARGs) were located in two clusters borne by two of the plasmids, comprising a class 1 integron that contained up to 14 ARGs including a VIM-1 metallo-β-lactamase gene, and an IS26 transposon that contained a mobile element from Acinetobacter baumannii encoding the amikacin resistance gene aac(6')-Ian. A MDR isolate obtained 6 years previously was identified (KP1048) retrospectively and was sequenced. Comparison of the two genomes showed that chromosomal mutations in outer membrane porins as well as mutations in the ramR and phoQ genes contributed to increase the resistance spectrum.

Community-Onset Bloodstream and Other Infections, Caused by Carbapenemase-Producing Enterobacteriaceae: Epidemiological, Microbiological, and Clinical Features

Background. Because most infections caused by carbapenemase-producing Enterobacteriaceae (CPE) begin during hospitalization, there are limited data about community-onset (CO) infections caused by CPE. Our aim is to describe the frequency of CO infections caused by CPE as well as the clinical features of CO bloodstream infections (CO-BSIs).

Methods. This study includes retrospective case series of CO infections caused by CPE in a tertiary hospital from January 2010 to July 2014. Any clinical sample with a positive culture for CPE that had been ordered by primary care doctors or by doctors at the emergency room (ER) were classified as CO. Epidemiological and microbiological features of CO cases were assessed as were clinical features of CO-BSIs.

Results. Of 780 clinical samples with CPE, 180 were requested at the ER or by primary care doctors (22.9%), 150 of which were produced by Klebsiella pneumoniae (83.3%). The bla_OXA−48 gene was detected in 149 isolates (82.8%) followed by the bla_VIM gene, 29 (16.1%). Sixty-one patients (33.9%) had a prior history of CPE infection/colonization. Thirty-four of the 119 (28.6%) patients without prior history of CPE infection/colonization did not fulfill Friedman criteria for healthcare-associated infections (HAIs). Considering previous hospitalization of up to 12 months as a criterion for defining HAI, only 16 (13.4%) cases were identified as community-acquired infections. The most frequent positive sample was urine (133 of 180; 73.9%). Twenty-one (11.7%) patients had a BSI, 9 of them secondary to urinary tract infections (42.9%). Thirty-day crude mortality among patients with BSI was 23.8% (5 of 21).

Conclusions. Community-onset infections caused by CPE are an important subgroup of all CPE infections. The urinary tract is the main source. Bloodstream infections accounted for more than 10% of the cases.

Clinical Characteristics of Carbapenem-resistant Klebsiella pneumoniae Infections in Ill and Colonized Children in Colombia

BACKGROUND

Multidrug-resistant Gram-negative infections represent a growing problem and a serious global threat. Data in children are scarce. Klebsiella pneumoniae carbapenemases (KPC) are the most common mechanism of resistance this organism has developed. We report the clinical characteristics and outcomes from a cohort of children infected or colonized with carbapenem-resistant K. pneumoniae (CRKp) at a tertiary care center in Medellín, Colombia.

METHODS

We performed a retrospective chart review of all pediatric cases from whom CRKp isolates were obtained from 2008 to 2013. Clinical characteristics and outcomes were recorded.

RESULTS

A total of 34 infected children (median age, 22.8 months) with 43 episodes and 55 colonized patients (median age, 33 months) were identified. All patients had at least 1 risk factor previously related with multidrug-resistant Gram-negative infections (premorbid conditions, previous exposure to antibiotics, prolonged length of stay and use of indwelling devices). Urinary tract infections, abdominal infections and bacteremia were the most common clinical presentations. Overall mortality was 38%, and it was lower when a meropenem-containing regimen was used. Colistin was the most used antibiotic either alone or in combination and was associated with 8.8% of nephrotoxicity.

CONCLUSION

CRKp infections have high mortality in children and usually occur in children with comorbidities, prolonged hospital stay and prior antibiotic exposure. Combined therapy with meropenem-containing regimens seems to be the best option in severely ill children.

Carbapenem-Resistant Enterobacteriaceae Infections in Children

Carbapenem-resistant Enterobacteriaceae (CRE) are an emerging global public health threat. Infections due to CRE are associated with significant morbidity and mortality. Few therapeutic options are available for treatment of these infections, and optimal antibiotic treatment regimens are unclear. Along with the rapidly increasing prevalence of CRE in the USA and worldwide, several studies have described the epidemiology of CRE in the adult population. While CRE are now also reported sporadically in children, there is a significant lack of data on the epidemiology, risk factors, treatment, and outcomes in this population. This article provides a comprehensive review of what is known to date about CRE, including clinical and molecular epidemiology, microbiologic diagnosis, antibiotic treatment options, and outcomes. In particular, this review will focus on the available data on CRE in the pediatric population.

Molecular epidemiology of VIM-1 producing Escherichia coli from Germany referred to the National Reference Laboratory

The distribution of carbapenemase genes in Escherichia coli strains isolated between September 2009 and May 2013 in Germany was investigated. Out of 192 isolates with carbapenemase production OXA-48 was found in 44.8%, VIM-1 in 18.8%, NDM-1 in 11.5% and KPC-2 in 6.8%. Patients with VIM-1 producing E. coli (n=36) differed from patients with OXA-48 by an older age, less frequent mention of travel history and an increased proportion of clinical over screening specimens. These data might indicate that introduction from abroad is of minor importance for VIM-1 producing E. coli compared to other carbapenemases. Multilocus sequence typing revealed that E. coli with VIM-1 were mostly multiclonal, emphasizing the role of horizontal gene transfer in its spread. Susceptibility testing of VIM-1 producing E. coli demonstrated aztreonam susceptibility in 55.6%. Among non-β-lactams susceptibility rates of >90% were observed for amikacin, tigecycline, colistin, fosfomycin and nitrofurantoin.

[The threat of the carbapenemase-producing enterobacteriaceae in Spain: positioning report of the SEIMC study groups, GEIH and GEMARA]

The emergence and spread of carbapenemase-producing Enterobacteriaceae (CPE), as the current paradigm of extensive drug-resistance and multi-drug resistance to antibiotics, is a serious threat to patient health and public health. The increase in OXA-48- and VIM-1-producing Klebsiella pneumoniae isolates represents the greatest impact of CPE in Spain. This evidence has lead the members of a representative panel of the Spanish Study Groups of Nosocomial Infections and Mechanisms of Action and Resistance to Antimicrobials of the Spanish Society of Clinical Microbiology and Infectious Diseases (GEIH/GEMARA-SEIMC) to make a position statement expressing the need for: (i) definitive and coordinated action by all health professionals and authorities involved, and (ii) an adaptation of health systems to facilitate their early control and minimize their impact.

Bugs, hosts and ICU environment: countering pan-resistance in nosocomial microbiota and treating bacterial infections in the critical care setting

ICUs are areas where resistance problems are the largest, and these constitute a major problem for the intensivist's clinical practice. Main resistance phenotypes among nosocomial microbiota are (i) vancomycin-resistance/heteroresistance and tolerance in grampositives (MRSA, enterococci) and (ii) efflux pumps/enzymatic resistance mechanisms (ESBLs, AmpC, metallo-betalactamases) in gramnegatives. These phenotypes are found at different rates in pathogens causing respiratory (nosocomial pneumonia/ventilator-associated pneumonia), bloodstream (primary bacteremia/catheter-associated bacteremia), urinary, intraabdominal and surgical wound infections and endocarditis in the ICU. New antibiotics are available to overcome non-susceptibility in grampositives; however, accumulation of resistance traits in gramnegatives has led to multidrug resistance, a worrisome problem nowadays. This article reviews microorganism/infection risk factors for multidrug resistance, suggesting adequate empirical treatments. Drugs, patient and environmental factors all play a role in the decision to prescribe/recommend antibiotic regimens in the specific ICU patient, implying that intensivists should be familiar with available drugs, environmental epidemiology and patient factors.

Carbapenemases: Partners in crime

Carbapenemases, β-lactamases that inactivate carbapenems and most β-lactam antibiotics, are most widely known for their ability to confer resistance to β-lactams. They include serine carbapenemases, such as the widespread KPC family of enzymes, and the metallo-β-lactamases that contain the IMP, NDM and VIM enzyme families acquired by Gram-negative bacteria on transferable elements. These enzymes are almost always produced by organisms that encode at least one other β-lactamase, with as many as eight different β-lactamase genes detected in a single isolate. This consortium of β-lactamases includes a full spectrum of molecular and biochemical characteristics, providing the producing organism with a range of catalytic activities. In addition to the variety of β-lactamases found in carbapenemase-producing Gram-negative pathogens are multiple other resistance factors, especially aminoglycoside-modifying enzymes and 16S rRNA methylases that confer resistance to aminoglycosides. Other acquired genes encode fluoroquinolone, trimethoprim, sulfonamide, rifampicin and chloramphenicol resistance determinants on mobile elements that travel together with β-lactamase genes. Thus, the recent proliferation of transferable carbapenemases serves to magnify resistance to virtually all antibiotic classes. Judicial use of current antibiotics and a quest for novel antibacterial agents are necessary, as multidrug-resistant bacteria continue to multiply.

Rapid evolution and spread of carbapenemases among Enterobacteriaceae in Europe

Plasmid-acquired carbapenemases in Enterobacteriaceae, which were first discovered in Europe in the 1990s, are now increasingly being identified at an alarming rate. Although their hydrolysis spectrum may vary, they hydrolyse most β-lactams, including carbapenems. They are mostly of the KPC, VIM, NDM and OXA-48 types. Their prevalence in Europe as reported in 2011 varies significantly from high (Greece and Italy) to low (Nordic countries). The types of carbapenemase vary among countries, partially depending on the cultural/population exchange relationship between the European countries and the possible reservoirs of each carbapenemase. Carbapenemase producers are mainly identified among Klebsiella pneumoniae and Escherichia coli, and still mostly in hospital settings and rarely in the community. Although important nosocomial outbreaks with carbapenemase-producing Enterobacteriaceae have been extensively reported, many new cases are still related to importation from a foreign country. Rapid identification of colonized or infected patients and screening of carriers is possible, and will probably be effective for prevention of a scenario of endemicity, as now reported for extended-spectrum β-lactamase (mainly CTX-M) producers in all European countries.

Carbapenem-resistant enterobacteriaceae: an emerging problem in children

Antibiotic resistance among gram-negative bacteria has reached critical levels. The rise of carbapenem resistance in Enterobacteriaceae carrying additional resistance genes to multiple antibiotic classes has created a generation of organisms nearly resistant to all available therapy. Carbapenem-resistant Enterobacteriaceae (CRE) infections are known to be associated with significant morbidity and mortality, and these pathogens have now made their way to the most vulnerable populations, including children. This review provides a brief overview of CRE, with a focus on CRE infections in children, and highlights available data on the epidemiology, clinical characteristics, carbapenemase types, risk factors, treatment, and outcomes of these multi-drug resistant infections in the pediatric population.

Fecal carriage of carbapenemase-producing Enterobacteriaceae: a hidden reservoir in hospitalized and nonhospitalized patients

Fecal carriage of carbapenemase-producing Enterobacteriaceae (CPE) has not been extensively investigated, except in the cases of selected patients at risk, mostly during outbreaks. A total of 1,100 fecal samples randomly collected in our institution in two different periods in 2006 (n = 600) and 2009-2010 (n = 500) from hospitalized (26.8%) and nonhospitalized (73.2%) patients were screened for CPE. The first period coincided with an outbreak of VIM-1-producing Enterobacteriaceae, and the second one coincided with the emergence of KPC enzymes in our hospital. Diluted samples in saline were cultured in Luria-Bertani broth with 1 μg/ml imipenem and subcultured in MacConkey agar plates with 4 μg/ml ceftazidime. Growing colonies were screened for CPE (modified Hodge test and EDTA and boronic acid synergy tests). Carbapenemase genes, plasmids in which they are located, and clonal relatedness were determined. Individuals who exhibited fecal carriage of CPE (11/1,043, 1.1%; 95% confidence interval [CI], 0.53 to 1.88) included 8 hospitalized (carriage rate, 2.9%; 95% CI, 1.24 to 5.55) and 3 nonhospitalized patients (carriage rate, 0.4%; 95% CI, 0.08 to 1.14), the latter being identified in 2009. Eighty-two percent of colonized patients were not infected with CPE. Isolates harboring bla(VIM-1) with or without bla(SHV-12) were identified as Klebsiella pneumoniae (n = 8; ST39, ST688, ST253, and ST163), Enterobacter cloacae (n = 3; two pulsed-field gel electrophoresis [PFGE] types), Escherichia coli (n = 2; ST155 and ST2441), and Citrobacter freundii (n = 1). Some of these lineages had previously been detected in our institution. The bla(VIM-1) gene was a member of the class 1 integrons In110 (bla(VIM-1)-aacA4-aadA1) and In113 (bla(VIM-1)-aacA4-dhfrII) located on plasmids IncN (n = 11; 30 to 50 kb) and IncHI2 (n = 3; 300 kb), respectively. Dissemination of bla(VIM-1) class-1 integrons within highly transferable plasmids in a polyclonal population has potentially contributed to the maintenance and spread of CPE.

Nosocomial outbreak of VIM-1-producing Klebsiella pneumoniae isolates of multilocus sequence type 15: molecular basis, clinical risk factors, and outcome

We study the epidemiology, molecular basis, clinical risk factors, and outcome involved in the clonal dissemination of VIM-1-producing Klebsiella pneumoniae isolates in the hospital setting. All patients infected/colonized by carbapenem-nonsusceptible K. pneumoniae (CNSKP) in 2009 were included. Molecular epidemiology was studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Antibiotic resistance genes were analyzed by PCR and sequencing. Plasmids were studied by PFGE with S1 nuclease digestion and for incompatibility group by a PCR-based replicon typing scheme. Risk factors associated with CNSKP colonization/infection were assessed by an observational case-control study. All 55 patients studied were infected (n = 28) or colonized (n = 27) by VIM-1-producing K. pneumoniae. All but one acquired isolates of a single clone (PFGE cluster 1 [C1], sequence type 15 [ST15]), while another clone (PFGE C2, ST340) was detected in four patients. C1 isolates also produced the new extended-spectrum β-lactamase SHV-134. bla(VIM-1) was carried in a class 1 integron and an untypeable plasmid of ∼50 bp. The number of days that the patient received mechanical ventilation, the use of parenteral nutrition, previous treatment with linezolid, and treatment with extended-spectrum cephalosporins for more than 7 days were detected to be independent risk factors for CNSKP acquisition. The VIM-1-producing K. pneumoniae ST15 clone has a high capacity to spread among intensive care unit patients with severe underlying conditions. A high rate of associated mortality and great difficulty in controlling the spread of this clone, without permanent behavioral changes in the personnel, were observed.

Evaluation of the VITEK 2 AST-N111 card for detection of extended-spectrum beta-lactamases (ESBLs) in Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca compared to ESBL Etests and combination disk methods

The VITEK 2 AST-N111 card was evaluated for detection of extended-spectrum beta-lactamases (ESBLs) by testing 51 ESBL positive and 50 ESBL negative isolates of E. coli, K. pneumoniae, and K. oxytoca. The occurrence of beta-lactamase genes was confirmed by PCR and sequencing. The advanced expert system (AES) of the VITEK 2 system achieved sensitivity and specificity values of 100% and 96.0%, respectively. The ESBL test of the VITEK 2 AST-N111 card showed a sensitivity of 92.1% and a specificity of 90.0%. Contradictory results obtained with the two VITEK 2 tools could be clarified by combination disk tests in nine of 11 isolates. The combined use of AES and ESBL tests of the AST-N111 card in association with combination disk tests in case of contradictory results seems to be a reliable method for ESBL detection.

Outbreak of vim-1-carbapenemase-producing Enterobacter cloacae in a pediatric intensive care unit

Pediatric patients are rarely infected with metallo-β-lactamase-producing Enterobacteriaceae. We describe 3 cases of children infected with VIM-1-producing clonal Enterobacter cloacae. Patients were treated with amikacin and cotrimoxazole. The blaVIM-1 gene was carried into a class 1 integron and an IncHI2 incompatibility group plasmid. Emergence of pediatric infections caused by carbapenemases-producing Enterobacteriaceae is a critical issue as they are resistant to most β-lactam antibiotics.

Emergence of VIM-1 metallo-β-lactamase-producing Escherichia coli in a neonatal intensive care unit

A carbapenem-resistant Escherichia coli isolate was recovered from rectal swab of a 12-day-old female neonate, which was admitted to a Greek neonatal intensive care unit (NICU). Phenotypic testing, polymerase chain reaction assays with sequencing, and plasmid analysis revealed that the isolate harbored a plasmid-mediated bla(VIM-1) metallo-β-lactamase gene. The appearance of a metallo-β-lactamase-producing E. coli in NICU is worrisome. Further surveys are needed to determine whether such Enterobacteriaceae may also be spreading in other NICUs.

[Interpretive reading of enterobacteria antibiograms]

The resistance pattern observed in the antibiogram of an isolate should be the sum of its natural resistance pattern, characteristic of the species, plus the acquired resistances. In Enterobacteriaceae, the production of inactivating enzymes is the main mechanism of resistance to beta-lactams and aminoglycosides. Each one of these enzymes recognizes one or more specific beta-lactams or aminoglycosides as substrate. This substrate specificity implies a specific resistance pattern from which we can deduce the enzymes present in the isolate. However, enzymatic-mediated resistance is not the only mechanism implicated and resistance is frequently multifactorial. Resistance to quinolones is mainly due to precise, sequential chromosomal mutations that can be selected by fluoroquinolone treatments. Recently, certain plasmid-mediated genes which code enzymes that modify quinolones or that are target protectors have been implicated in the low level resistance to quinolones.

Carbapenem-resistant KPC-2-producing Escherichia coli in a Tel Aviv Medical Center, 2005 to 2008

All of the carbapenem-resistant Escherichia coli (CREC) isolates identified in our hospital from 2005 to 2008 (n = 10) were studied. CREC isolates were multidrug resistant, all carried bla(KPC-2), and six of them were also extended-spectrum beta-lactamase producers. Pulsed-field gel electrophoresis indicated six genetic clones; within the same clone, similar transferable bla(KPC-2)-containing plasmids were found whereas plasmids differed between clones. Tn4401 elements were identified in all of these plasmids.