Prevalence of clinical isolates of Escherichia coli producing inhibitor-resistant beta-lactamases at a University Hospital in Barcelona, Spain, over a 3-year period

First Record of Dissemination of BLBLI-Resistant Enterobacter cloacae from Public Hospitals in Baghdad, Iraq

Background:

Enterobacter cloacae are most frequently isolated from human clinical specimens.

Objective:

This cross-sectional study aimed to investigate the dissemination of E. cloacae clinical isolates resistant to β-lactam-β-lactamase inhibitor (BLBLI) combinations from different clinical specimens of hospitalized patients.

Methods:

E. cloacae isolates were recovered from different clinical samples of hospitalized patients in three main hospitals in Baghdad city. E. cloacae isolates were identified based on their morphology and biochemical tests, and the identification was confirmed using Vitek-2 system. The antibiotic susceptibility testing of E. cloacae isolates to a variety of antibiotics was achieved using disc diffusion test (DDT) and Vitek-2 system.

Results:

Results found that among 335 culture-positive samples, 30 isolates (8.9%) belonged to E. cloacae. A high rate of isolation was observed in urine isolates (46.6%), followed by wounds (burns) isolates (26.6%). Out of 30 E. cloacae strains isolated during this study, 18 (60%) showed reduced susceptibility to BLBLI combinations. TEM genes (TEM-1 and TEM-2) were successfully amplified from 7/18 isolates (38.8%) and high rate of BLBLI genes was detected (CTX-M, bla-SHV, SHV-2, and OXA-1). However, no BLBLI genes of bla-AmpC, bla- OXA-2, and bla- OXA-10 were found in E. cloacae isolates when tested using specific primers for bla-AmpC and bla-OXA genes.

Conclusion:

From this study, we can conclude that the production of inhibitor-resistant β-lactamases by E. cloacae isolates could be increasingly common in nosocomial pathogens other than E. coli or K. pneumoniae in public hospitals in Baghdad, Iraq.

Prevalence of and risk factors for extended-spectrum beta-lactamase genes carriership in a population-based cohort of middle-aged and elderly

INTRODUCTION

Increasing resistance to beta-lactam antibiotics is an alarming development worldwide. Fecal carriership of TEM, SHV, CTX-M and CMY was studied in a community-dwelling population of middle-aged and elderly individuals.

PATIENTS AND METHODS

Feces was obtained from individuals of the Rotterdam Study. Carriership of the TEM, SHV, CTX-M and CMY genes was determined using real-time polymerase chain reaction (qPCR). Possible associations were investigated between carriership of these genes and several risk factors, such as the use of antimicrobial drugs, diabetes mellitus, protein pump inhibitor (PPI) use, travelling, the composition of the gut microbiota, and intake of certain foods.

RESULTS

The most prevalent gene was TEM (53.0%), followed by SHV (18.4%), CTX-M (5.4%) and CMY (3.6%). Use of penicillins with extended spectrum was associated with TEM carriership, whereas use of macrolides and lincosamides was associated with TEM and SHV carriership. Interestingly, use of PPIs was associated with a higher prevalence of carriership of TEM, SHV and CMY (TEM: odds ratio [OR] 1.34; 95% confidence interval [CI] 1.05-1.77; SHV: OR 2.17; 95%CI 1.55-2.87; CMY: OR 2.26; 95%CI 1.23-4.11). Furthermore, associations were found between the richness and composition of the gut microbiota and TEM and SHV carriership.

CONCLUSIONS

The prevalence of carriership of TEM was substantial, but the prevalence of carriership of the extended-spectrum β-lactamase gene, CTX-M and the AmpC β-lactamase gene, CMY was relatively low in this community-dwelling, population-based cohort. The composition of the microbiota might play a role in the retention of resistance genes, but future studies are necessary to further elucidate this relationship.

Exploring the genetic mechanisms underlying amoxicillin-clavulanate resistance in waterborne Escherichia coli

Escherichia coli is a human commensal and faecal indicator bacteria which is also the etiologic agent of several nosocomial- and community-acquired infections. Amoxicillin-clavulanate (AMC) is a widely prescribed β-lactam/β-lactamase inhibitor which is used against E. coli infections. Resistance to AMC in E. coli has been primarily attributed to point mutations in bla_TEM-1 resulting in inhibitor-resistant TEM (IRT) β-lactamases. In this study, we have explored the reasons underlying AMC-resistance in waterborne E. coli. Most of the studies regarding IRT-producing E. coli have been conducted on clinical samples and studies exploring genetic mechanisms underlying AMC-resistance in aquatic E. coli are scarce. Since, bla_TEM-1 and several antimicrobial resistance determinants are located on mobile genetic elements they can easily disseminate among other microbes inhabiting urban waterbodies. Thus, it is important to understand the underlying mechanisms to check the dissemination of AMC-resistance in other waterborne pathogens. Our results indicated that AMC-resistant E. coli were susceptible to other β-lactam/β-lactamase inhibitors like, ampicillin/sulbactam and piperacillin/tazobactam. Though, bla_TEM-1 was present, none of the strains harbored point mutations which could qualify as IRT and only one strain harbored both bla_TEM-1 and bla_OXA-1. Hyperproduction of bla_TEM-1, presence of plasimd-mediated ampC or promoter/attenuator mutations in the chromososmal ampC might not be related to IRT-like phenotype or AMC-resistance. This suggests that other mechanisms like, increased plasmid copy numbers or gene amplification or deficiency in the expression/function of porins might be responsible for AMC-resistance in waterborne E. coli.

Distribution of integrons and phylogenetic groups among Escherichia coli causing community-acquired urinary tract infection in Upper Egypt

Escherichia coli is a major cause of community-acquired urinary tract infections (CA-UTIs). In this study, we investigated the antimicrobial resistance patterns, the distribution of phylogenetic groups, and the prevalence and characteristics of integron-bearing E. coli isolates from outpatients with CA-UTIs in El-Minia governorate, in Upper Egypt. Out of the 583 urine samples collected, 134 were positive for E. coli, from which the most resistant isolates (n = 80) were selected for further analysis. The majority of these isolates (62.5%, 50/80) showed multidrug resistance profiles. Group B2 was the most predominant phylogenetic group (52.5%), followed by group F (21.25%), Clades I or II (12.5%), and finally isolates of unknown phylogroup (13.75%). Of the 80 isolates, 7 (8.75%) carried class 1 integrons, which contained 3 different types of integrated gene cassettes, including those conferring resistance to streptomycin/spectinomycin, trimethoprim, and some open reading frames of unknown function (gcuF). In conclusion, the types and combinations of the gene cassettes in our study may reflect the specific selective pressures to which the isolates were subjected within the study region, therefore, providing valuable data for future intervention strategies that are precisely tailored to prevent the dissemination of the uropathogenic E. coli strains circulating within Upper Egypt.

Molecular Characterization Of Pathogenic Salmonella Spp From Raw Beef In Karachi, Pakistan

The aim of the present study was to estimate the prevalence of Salmonella and investigate the dominant serovars distribution in raw beef and to screen the isolated serovars for the prescense of beta-lactamases and virulence genes. A total of 150 samples of raw beef sold at butcher shops (n = 75) and supermarkets (n = 75) in Karachi city were collected (50 samples each from muscles, lymph nodes, and minced beef). The samples were cultured according to the ISO-6579-1guidlines. The overall prevalence of Salmonella strains was found to be 21.34%. A total of 56 isolates of Salmonella belonging to four serogroups (Salmonella Pullorum, Salmonella Enteritidis, Salmonella Typhimurium and Salmonella Choleraesuis) were isolated from beef muscles (12%), lymph nodes (24%) and minced beef (28%) samples collected from butcher shops (av. 21.34%). No Salmonella was detected in beef samples collected from supermarkets. S. Enteritidis contamination was highest (37.5 %), followed by S. Choleraesuis (30.4%), S. Pullorum (19.6%) and S. Typhimurium (12.5 %). Antibiotic susceptibility testing revealed that Salmonella isolates were highly resistant to Oxytetracycline (90%), Ampicillin (90.5%), Amoxicillin (81.1%), Tetracycline (76%), Neomycin, (79.8%) and Ciprofloxacin (61.4%). The Salmonella isolates examined were more susceptible to the Cephalosporin antibiotics such as Cefixime (43.2%), Cefepime (48.2) and Cefoxitin (49.8%). PCR based screening of blaTEM, blaCTX-M and blaSHV revealed that blaCTX-M and blaTEM were the dominant resistant genes in S. Enteritidis and S. Typhimurium followed by S. Pullorum and S. Choleraesuis whereas blaSHV was the least detected beta-lactamase in Salmonella isolates. Virulence genes screening revealed that at least five genes were present in all the serovars, highest being present in S. Enteritidis (12/17) and S. Typhimurium (12/17). S. Cholerasuis (5/17) carried the least number of virulence genes followed by S. Pullorum (6/17). The present data suggest that beef samples from butcher shops of Karachi city are heavily contaminated with MDR Salmonella. The presence of resistance and virulence genes in MDR strains of Salmonella may play a significant role in transmission and development of Salmonella infection in humans.

High prevalence and diversity of extended-spectrum β-lactamase and emergence of OXA-48 producing Enterobacterales in wildlife in Catalonia

Most of the studies focused on antimicrobial resistance (AMR) performed in wildlife describe Escherichia coli as the principal indicator of the selective pressure. In the present study, several species of Enterobacterales with a large panel of cephalosporin resistant (CR) genes have been isolated from wildlife in Catalonia. A total of 307 wild animals were examined to determine the prevalence of CR enterobacteria, AMR phenotypes and the presence of common carbapenem and CR genes. The overall prevalence of CR-phenotype was 13% (40/307): 17.3% in wild mammals (18/104) and 11.5% in wild birds (22/191) (p<0.01). Hedgehogs showed the highest prevalence (13.5% of 104) of the mammal specimens, and raptors the highest in bird specimen (7.3% of 191). Although CR E. coli was the most frequently isolated (45%), other CR- Enterobacterales like Klebsiella pneumoniae (20%), Citrobacter freundii (15%), Enterobacter cloacae (5%), Proteus mirabilis (5%), Providencia spp (5%) and Serratia marcescens (2.5%) were also isolated. A high diversity of CR genes was identified among the isolates, with 50% yielding blaCMY-2, 23% blaSHV-12, 20% blaCMY-1 and 18% blaCTX-M-15. Additionally, resistance to carbapenems associated to OXA-48 gene was found. Most of the CR isolates, principally K. pneumoniae and C. freundii, were multi-resistant with co-resistance to fluoroquinolones, tetracycline, sulphonamides and aminoglycosides. This study reports high prevalence of Enterobacterales harbouring a variety of CR genes and OXA-48 mediated-carbapenem resistance, all of them frequently associated to nosocomial human infections, for the first time in wild mammals and wild birds. Implementation of control measures to reduce the impact of anthropogenic pressure in the environment is urgently needed.

Phage selection restores antibiotic sensitivity in MDR Pseudomonas aeruginosa

Increasing prevalence and severity of multi-drug-resistant (MDR) bacterial infections has necessitated novel antibacterial strategies. Ideally, new approaches would target bacterial pathogens while exerting selection for reduced pathogenesis when these bacteria inevitably evolve resistance to therapeutic intervention. As an example of such a management strategy, we isolated a lytic bacteriophage, OMKO1, (family Myoviridae) of Pseudomonas aeruginosa that utilizes the outer membrane porin M (OprM) of the multidrug efflux systems MexAB and MexXY as a receptor-binding site. Results show that phage selection produces an evolutionary trade-off in MDR P. aeruginosa, whereby the evolution of bacterial resistance to phage attack changes the efflux pump mechanism, causing increased sensitivity to drugs from several antibiotic classes. Although modern phage therapy is still in its infancy, we conclude that phages, such as OMKO1, represent a new approach to phage therapy where bacteriophages exert selection for MDR bacteria to become increasingly sensitive to traditional antibiotics. This approach, using phages as targeted antibacterials, could extend the lifetime of our current antibiotics and potentially reduce the incidence of antibiotic resistant infections.

β-Lactamases in amoxicillin-clavulanate-resistant Escherichia coli strains isolated from a Chinese tertiary hospital

A total of 52 strains were resistant to amoxicillin-clavulanate by disk diffusion method in a Chinese tertiary hospital from July 2011 to December 2011. Among these isolates, 2 isolates possessed a phenotype consistent with production of inhibitor-resistant temoniera (TEM) (IRT) β-lactamase, and the TEM-type gene was cloned into strains of Escherichia coli JM109 cells. Both had no blaTEM mutations and were identified as TEM-1 β-lactamase producers. As a result, no IRT β-lactamase was detected. Multiplex PCR detected most of these strains produced TEM-1 enzymes, and plasmid-mediated AmpC β-lactamase and oxacillinase-1 β-lactamases are important mechanisms of resistance as well.

Analysis of β-lactamase phenotypes and carriage of selected β-lactamase genes among Escherichia coli strains obtained from Kenyan patients during an 18-year period

Background

Although β-lactam antibiotics are heavily used in many developing countries, the diversity of β-lactamase genes (bla) is poorly understood. We screened for major β-lactamase phenotypes and diversity of bla genes among 912 E. coli strains isolated from clinical samples obtained between 1992 and 2010 from hospitalized and non-hospitalized patients.

Results

None of the isolates was resistant to carbapenems but 30% of all isolates were susceptible to cefepime, cephamycins and piperacillin-tazobactam. Narrow spectrum β-lactamase (NSBL) phenotype was observed in 278 (30%) isolates that contained bla_TEM-1 (54%) or bla_SHV-1 (35%) or both (11%). Extended Spectrum β-lactamase (ESBL) phenotype was detected in 247 (27%) isolates which carried bla_CTX-M-14 (29%), bla_CTX-M-15 (24%), bla_CTX-M-9 (2%), bla_CTX-M-8 (4%), bla_CTX-M-3 (11%), bla_CTX-M-1 (6%), bla_SHV-5 (3%), bla_SHV-12 (5%), and bla_TEM-52 (16%). Complex Mutant TEM-like (CMT) phenotype was detected in 220 (24%) isolates which carried bla_TEM-125 (29%), while bla_TEM-50, bla_TEM-78, bla_TEM-109, bla_{TEM −152} and bla_TEM-158 were detected in lower frequencies of between 7% and 11%. Majority of isolates producing a combination of CTX-M-15 + OXA-1 + TEM-1 exhibited resistance phenotypes barely indistinguishable from those of CMT-producers. Although 73 (8%) isolates exhibited Inhibitor Resistant TEM-like (IRT) phenotype, bla_TEM-103 was the only true IRT-encoding gene identified in 18 (25%) of strains with this phenotype while the rest produced a combination of TEM-1 + OXA-1. The pAmpCs-like phenotype was observed in 94 (10%) isolates of which 77 (82%) carried bla_CMY-2 while 18% contained bla_CMY-1.

Isolates from urine accounted for 53%, 53%, 74% and 72% of strains exhibiting complex phenotypes such as IRT, ESBL, CMT or pAmpC respectively. On the contrary, 55% isolates from stool exhibited the relatively more susceptible NSBL-like phenotype. All the phenotypes, and majority of the bla genes, were detected both in isolates from hospitalized and non-hospitalized patients but complex phenotypes were particularly common among strains obtained between 2000 and 2010 from urine of hospitalized patients.

Conclusions

The phenotypes and diversity of bla genes in E. coli strains implicated in clinical infections in non-hospitalized and hospitalized patients in Kenya is worryingly high. In order to preserve the efficacy of β-lactam antibiotics, culture and susceptibility data should guide therapy and surveillance studies for β-lactamase-producers in developing countries should be launched.

Spanish multicenter study of the epidemiology and mechanisms of amoxicillin-clavulanate resistance in Escherichia coli

We conducted a prospective multicenter study in Spain to characterize the mechanisms of resistance to amoxicillin-clavulanate (AMC) in Escherichia coli. Up to 44 AMC-resistant E. coli isolates (MIC ≥ 32/16 μg/ml) were collected at each of the seven participant hospitals. Resistance mechanisms were characterized by PCR and sequencing. Molecular epidemiology was studied by pulsed-field gel electrophoresis (PFGE) and by multilocus sequence typing. Overall AMC resistance was 9.3%. The resistance mechanisms detected in the 257 AMC-resistant isolates were OXA-1 production (26.1%), hyperproduction of penicillinase (22.6%), production of plasmidic AmpC (19.5%), hyperproduction of chromosomic AmpC (18.3%), and production of inhibitor-resistant TEM (IRT) (17.5%). The IRTs identified were TEM-40 (33.3%), TEM-30 (28.9%), TEM-33 (11.1%), TEM-32 (4.4%), TEM-34 (4.4%), TEM-35 (2.2%), TEM-54 (2.2%), TEM-76 (2.2%), TEM-79 (2.2%), and the new TEM-185 (8.8%). By PFGE, a high degree of genetic diversity was observed although two well-defined clusters were detected in the OXA-1-producing isolates: the C1 cluster consisting of 19 phylogroup A/sequence type 88 [ST88] isolates and the C2 cluster consisting of 19 phylogroup B2/ST131 isolates (16 of them producing CTX-M-15). Each of the clusters was detected in six different hospitals. In total, 21.8% of the isolates were serotype O25b/phylogroup B2 (O25b/B2). AMC resistance in E. coli is widespread in Spain at the hospital and community levels. A high prevalence of OXA-1 was found. Although resistant isolates were genetically diverse, clonality was linked to OXA-1-producing isolates of the STs 88 and 131. Dissemination of IRTs was frequent, and the epidemic O25b/B2/ST131 clone carried many different mechanisms of AMC resistance.

Characterization of a novel extended-spectrum β-lactamase phenotype from OXA-1 expression in Salmonella Typhimurium strains from Africa and Ireland

Salmonella enterica (S. Typhimurium) strains from Kenya, Malawi, and Ireland showing elevated cefepime MIC values carried bla(OXA-1). These strains were not detected by current guidelines for extended-spectrum β-lactamase production based on MIC values or clavulanate inhibition, since cefepime is a preferred substrate for OXA-1 and this enzyme is reported to be resistant to clavulanate inhibition. bla(OXA-1) was located within a class I integron and an activated P(2) promoter was identified upstream of bla(OXA-1). P(2) was activated by the insertion of a triplet 'GGG' upstream of the -10 signal. All African strains were ST313, prevalent in this continent, and the Irish isolate belonged to ST19.

Molecular characterization of resistance to extended-spectrum cephalosporins in clinical Escherichia coli isolates from companion animals in the United States

Resistance to extended-spectrum cephalosporins (ESC) among members of the family Enterobacteriaceae occurs worldwide; however, little is known about ESC resistance in Escherichia coli strains from companion animals. Clinical isolates of E. coli were collected from veterinary diagnostic laboratories throughout the United States from 2008 to 2009. E. coli isolates (n = 54) with reduced susceptibility to ceftazidime or cefotaxime (MIC ≥ 16 μg/ml) and extended-spectrum-β-lactamase (ESBL) phenotypes were analyzed. PCR and sequencing were used to detect mutations in ESBL-encoding genes and the regulatory region of the chromosomal gene ampC. Conjugation experiments and plasmid identification were conducted to examine the transferability of resistance to ESCs. All isolates carried the bla(CTX-M-1)-group β-lactamase genes in addition to one or more of the following β-lactamase genes: bla(TEM), bla(SHV-3), bla(CMY-2), bla(CTX-M-14-like), and bla(OXA-1.) Different bla(TEM) sequence variants were detected in some isolates (n = 40). Three isolates harbored a bla(TEM-181) gene with a novel mutation resulting in an Ala184Val substitution. Approximately 78% of the isolates had mutations in promoter/attenuator regions of the chromosomal gene ampC, one of which was a novel insertion of adenine between bases -28 and -29. Plasmids ranging in size from 11 to 233 kbp were detected in the isolates, with a common plasmid size of 93 kbp identified in 60% of isolates. Plasmid-mediated transfer of β-lactamase genes increased the MICs (≥ 16-fold) of ESCs for transconjugants. Replicon typing among isolates revealed the predominance of IncI and IncFIA plasmids, followed by IncFIB plasmids. This study shows the emergence of conjugative plasmid-borne ESBLs among E. coli strains from companion animals in the United States, which may compromise the effective therapeutic use of ESCs in veterinary medicine.

[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.

Population analysis and epidemiological features of inhibitor-resistant-TEM-beta-lactamase-producing Escherichia coli isolates from both community and hospital settings in Madrid, Spain

Punctual mutations in the TEM-1 or TEM-2 gene may lead to inhibitor-resistant-TEM (IRT) beta-lactamases with resistance to beta-lactam-beta-lactamase inhibitor combinations and susceptibility to cephalosporins. The aim of this work was to analyze the current epidemiology of IRT beta-lactamases in contemporary clinical Escherichia coli. Isolates were prospectively collected in our hospital (2007 and 2008) from both outpatients (59.8%) and hospitalized patients (40.2%). The genetic relationships of the isolates were determined by XbaI pulsed-field gel electrophoresis, multilocus sequence typing, and phylogenetic group analysis. IRT genes were sequenced and located by hybridization, and the incompatibility group of the plasmids was determined. From a total of 3,556 E. coli isolates recovered during the study period, 152 (4.3%) showed reduced susceptibility to amoxicillin-clavulanate, with 18 of them producing IRT enzymes (0.5%). These were mostly recovered from urine (77.8%). A high degree of IRT diversity was detected (TEM-30, -32, -33, -34, -36, -37, -40, and -54), and the isolates were clonally unrelated but were mostly associated with phylogenetic group B2 (55.5%). In 12 out of 16 (75%) isolates, the bla(IRT) gene was plasmid located and transferred by conjugation in 9 of them, whereas chromosomal localization was demonstrated in 4 isolates (25%). The sizes of the plasmids ranged from 40 kb (IncN) to 100 kb (IncFII, IncFI/FIIA), and they showed different restriction patterns by restriction fragment length polymorphism analysis. Unlike extended-spectrum beta-lactamase producers, the frequency of IRT producers remains low in both community and hospital settings, with most of them causing urinary tract infections. Although bla(IRT) genes are mainly associated with plasmids, they can be also located in the chromosome. Despite this situation, clonal expansion and/or gene dispersion was not observed, denoting the independent emergence of these enzymes.

Three decades of beta-lactamase inhibitors

Since the introduction of penicillin, beta-lactam antibiotics have been the antimicrobial agents of choice. Unfortunately, the efficacy of these life-saving antibiotics is significantly threatened by bacterial beta-lactamases. beta-Lactamases are now responsible for resistance to penicillins, extended-spectrum cephalosporins, monobactams, and carbapenems. In order to overcome beta-lactamase-mediated resistance, beta-lactamase inhibitors (clavulanate, sulbactam, and tazobactam) were introduced into clinical practice. These inhibitors greatly enhance the efficacy of their partner beta-lactams (amoxicillin, ampicillin, piperacillin, and ticarcillin) in the treatment of serious Enterobacteriaceae and penicillin-resistant staphylococcal infections. However, selective pressure from excess antibiotic use accelerated the emergence of resistance to beta-lactam-beta-lactamase inhibitor combinations. Furthermore, the prevalence of clinically relevant beta-lactamases from other classes that are resistant to inhibition is rapidly increasing. There is an urgent need for effective inhibitors that can restore the activity of beta-lactams. Here, we review the catalytic mechanisms of each beta-lactamase class. We then discuss approaches for circumventing beta-lactamase-mediated resistance, including properties and characteristics of mechanism-based inactivators. We next highlight the mechanisms of action and salient clinical and microbiological features of beta-lactamase inhibitors. We also emphasize their therapeutic applications. We close by focusing on novel compounds and the chemical features of these agents that may contribute to a "second generation" of inhibitors. The goal for the next 3 decades will be to design inhibitors that will be effective for more than a single class of beta-lactamases.

Increased amoxicillin-clavulanic acid resistance in Escherichia coli blood isolates, Spain

To determine the evolution and trends of amoxicillin–clavulanic acid resistance among Escherichia coli isolates in Spain, we tested 9,090 blood isolates from 42 Spanish hospitals and compared resistance with trends in outpatient consumption. These isolates were collected by Spanish hospitals that participated in the European Antimicrobial Resistance Surveillance System network from April 2003 through December 2006.

IRT and CMT beta-lactamases and inhibitor resistance

Acquired resistance to penicillin-beta-lactamase inhibitor combinations in Escherichia coli is due to: (i) penicillinase hyperproduction due to the presence of the bla(TEM-1) gene in small multicopy plasmids or strong promoters; (ii) overproduction of constitutive AmpC cephalosporinase; and (iii) OXA-type and inhibitor-resistant TEM (IRT) beta-lactamases. IRT enzymes emerge via mutational events from TEM-1 or TEM-2 beta-lactamases that affect substrate affinity for beta-lactamase inhibitors. They are mainly isolated in urinary infections from community patients. Prevalence is variable, depending on geographical area, detection methods and potential selection pressure. These enzymes may evolve into complex mutants (CMT enzymes), which also confer resistance to extended-spectrum cephalosporins. CTX-M enzymes with the IRT phenotype have not been detected to date. New studies of IRT enzymes, including population structure, association with virulence traits and plasmid dispersion, are needed.

Patterns of resistance to beta-lactams and characterization of beta-lactamases in Escherichia coli isolates from children in Tunisia

Seventy-six (75.2%) of 101 Escherichia coli isolates, collected over a 2-month period in 2002 at the Children's Hospital of Tunis (Tunisia), were resistant to at least one beta-lactam. They produced beta-lactamases which were further characterized by spectrophotometry, isoelectric focusing (IEF) and PCR. Seventy-five isolates had a pI 5.4 beta-lactamase and one isolate expressed a pI 5.6 beta-lactamase. These beta-lactamases were active against penicillins and cephalothin. Nineteen of 76 isolates were resistant to ticarcillin-clavulanic acid combination. The bla(TEM) gene was detected in 71 isolates, all expressed a pI 5.4 beta-lactamase that was assumed to be TEM-1 or inhibitor-resistant TEM (IRT). Thirty-eight of 76 isolates showed one weak band on IEF with pIs ranging from 8.2 to >9, suggesting low level expression of the chromosomal AmpC beta-lactamase. Five of 76 isolates produced extended-spectrum beta-lactamases (ESBLs), with a basic pI of 7.9 or 8.7, active on penicillins, extended-spectrum cephalosporins, but not on cefoxitin. bla(SHV) genes were detected in three isolates producing pI 7.9 ESBLs but not in two isolates expressing pI 8.7 ESBLs. These latter showed strong cefotaxime-hydrolyzing activities. Hence, they might be CTX-M-type ESBLs.

CTX-M-2 and a new CTX-M-39 enzyme are the major extended-spectrum beta-lactamases in multiple Escherichia coli clones isolated in Tel Aviv, Israel

The rate of occurrence of the extended-spectrum beta-lactamase (ESBL)-producing phenotype among Escherichia coli isolates in Tel Aviv is 12% (22). The aim of this study was to understand the molecular epidemiology of E. coli ESBL producers and to identify the ESBL genes carried by them. We studied 20 single-patient ESBL-producing E. coli clinical isolates. They comprised 11 distinct nonrelated pulsed-field gel electrophoresis (PFGE) genotypes: six isolates belonged to the same PFGE clone, four other clones included two isolates each, and six unrelated clones included only one isolate. All isolates produced various beta-lactamases with pIs ranging from 5.2 to 8.2, varying within similar PFGE clones. The most prevalent ESBL gene was bla(CTX-M); 16 isolates carried bla(CTX-M-2) and three carried a new ESBL gene designated bla(CTX-M-39). Three strains carried bla(SHV) (two bla(SHV-12) and one bla(SHV-5)), and two strains carried inhibitor-resistant ESBL genes, bla(TEM-33) and bla(TEM-30); 18 strains carried bla(TEM-1) and eight strains carried bla(OXA-2). Plasmid mapping and Southern blot analysis with a CTX-M-2 probe demonstrated that bla(CTX-M-2) is plasmid borne. The wide dissemination of ESBLs among E. coli isolates in our institution is partly related to clonal spread, but more notably to various plasmid-associated ESBL genes, occurring in multiple clones, wherein the CTX-M gene family appears almost uniformly. We report here a new CTX-M gene, designated bla(CTX-M-39), which revealed 99% homology with bla(CTX-M-26), with a substitution of arginine for glutamine at position 225.

Understanding the longevity of the beta-lactam antibiotics and of antibiotic/beta-lactamase inhibitor combinations

Microbial resistance necessitates the search for new targets and new antibiotics. However, it is likely that resistance problems will eventually threaten these new products and it may, therefore, be instructive to review the successful employment of beta-lactam antibiotic/beta-lactamase inhibitor combinations to combat penicillin resistance. These combination drugs have proven successful for more than two decades, with inhibitor resistance still being relatively rare. The beta-lactamase inhibitors are mechanism-based irreversible inactivators. The ability of the inhibitors to avoid resistance may be due to the structural similarities between the substrate and inhibitor.

CTX-M: changing the face of ESBLs in the UK

The UK has experienced a sudden rise in extended-spectrum beta-lactamase (ESBL) rates, largely due to the appearance and spread of Escherichia coli producing CTX-M-15 type beta-lactamase. The British Society for Antimicrobial Chemotherapy organized two update meetings during 2004 to report and discuss the recognition, clinical diagnosis, treatment and control of bacteria producing these beta-lactamases. This paper reports the data and reviews made by contributors to the conferences. The historical distribution and emergence of ESBLs was reviewed along with the emergence of plasmid-mediated CTX-M ESBLs following their mobilization from the chromosome of Kluyvera spp. The first significant outbreak of CTX-M producers in the UK occurred in 2001 and involved Klebsiella pneumoniae with CTX-M-26 at one site, but by 2003, cloned and diverse E. coli with CTX-M-15 were widespread, with Shropshire one of the most affected regions. The specific experience in Shropshire was reported on and a comprehensive review made of the level of awareness of the need for ESBL detection in laboratories in England and Wales, together with a description of the variety of methods that may be applied, with recommendations for optimal methodology. The increased mortality associated with inappropriate treatment of infections caused by ESBL-producing strains was highlighted, together with discussion on potential control of cross-infection. The meeting concluded that the CTX-M genes have now become widespread in not only E. coli but other Enterobacteriaceae in the UK and this will represent a substantial threat to both the treatment of infections caused by these bacteria in the community and within hospitals.

beta-Lactamases among extended-spectrum beta-lactamase (ESBL)-resistant Salmonella from poultry, poultry products and human patients in The Netherlands

OBJECTIVES

The purpose of this work was to study the genetic determinants responsible for extended-spectrum beta-lactamase (ESBL) resistance of Salmonella isolated from Dutch poultry, poultry meat and hospitalized humans.

METHODS

Thirty-four ESBL-resistant Salmonella isolates from The Netherlands were tested towards 21 antimicrobial agents. PCR and sequencing were used to determine the underlying genetic determinants responsible for the ESBL phenotypes. The transferability of the ESBL phenotypes was tested by conjugation to a susceptible Salmonella enterica serovar Dublin and plasmid purification, restriction fragment length polymorphism (RFLP) and pulsed-field gel electrophoresis (PFGE) were employed to further characterize a subset of the isolates.

RESULTS

A great genetic diversity was seen among the isolates. The bla(TEM-52) gene was most predominant and was found among Salmonella enterica serovars Blockley, Thomson, London, Enteritidis phage type 14b, Paratyphi B, Virchow and Typhimurium phage types 11 and 507. We also found the bla(TEM-20) gene in S. Paratyphi B var. Java and the bla(TEM-63) gene in S. Isangi. Furthermore, we detected the bla(CTX-M-28) gene in S. Isangi and the bla(CTX-M-3) gene in S. Typhimurium phage type 507. The bla(CTX-M-2) gene was identified in S. Virchow, which also contained a copy of the bla(SHV-2) gene and a copy of the bla(TEM-1) gene. The bla(SHV-12) gene was found alone in S. Concord and together with the bla(TEM-52) gene in S. Typhimurium. Finally, the bla(ACC-1) gene was cloned from a S. Bareilly isolate and was found to be present on indistinguishable plasmids in all S. Bareilly isolates examined as well as in a S. Braenderup isolate and a S. Infantis isolate.

CONCLUSIONS

Our data underscore the diversity of ESBL genes in Salmonella enterica isolated from animals, food products and human patients.

Isolation of an amikacin-resistant Escherichia coli strain after tobramycin treatment of previous recurrent episodes of respiratory tract infections caused by Pseudomonas aeruginosa

Amikacin-resistant Escherichia coli strains are isolated rarely from clinical samples. In the present study, investigation of an amikacin-resistant clinical isolate of E. coli demonstrated the presence of two class 1 integrons carrying the aacA4 gene plus the aacA7 gene, and the dfrA17 gene plus the aadA5 gene, respectively. Resistance to amikacin in this E. coli isolate was related to the presence of both aacA4 and aacA7.

Susceptibility of Escherichia coli to the amoxycillin-clavulanate combination: which recommendations should be used to provide relevant information to clinicians?

This study compared MIC distributions of amoxycillin-clavulanate obtained with NCCLS and French (Comite de l'Antibiogramme de la Societe Francaise de Microbiologie; CA-SFM) methodologies for Escherichia coli isolates from urine that were non-susceptible to amoxycillin-clavulanate by the disk diffusion method. With the NCCLS and CA-SFM methods, 74% and 13%, respectively, of these isolates were susceptible to amoxycillin-clavulanate. Therefore, the apparent relatively poor efficacy of amoxycillin-clavulanate against E. coli in French hospitals probably reflects a methodological difference rather than a localised resistance problem. This implies that amoxycillin-clavulanate could be used as an alternative to fluoroquinolones for treatment of E. coli urinary tract infections. Susceptibility tests for amoxycillin-clavulanate should be standardised worldwide.