Multiple outbreaks of nosocomial salmonellosis in Russia and Belarus caused by a single clone of Salmonella enterica serovar Typhimurium producing an extended-spectrum beta-lactamase

Prevalence and resistance to antibacterial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan

Background and Aim: Salmonella is one of the main causative agents of foodborne infections. The source of the pathogen, in most cases, is poultry products. The intensification of poultry farming and the constant and uncontrolled use of antimicrobials has led to an increase in the level of antibiotic resistance, especially in developing countries. This study aimed to determine the level of sensitivity to antimicrobial agents in Salmonella enterica strains isolated from poultry products in Northern Kazakhstan, as well as to determine the genetic mechanisms of resistance and the presence of integrons. Materials and Methods: In total, 398 samples of poultry products sold in Northern Kazakhstan were selected. Salmonella strains were isolated from product samples using microbiological methods. Salmonella was identified based on morphological, biochemical, and serological methods, as well as polymerase chain reaction (PCR). Sensitivity testing for antimicrobial agents was performed using the disk diffusion method. The detection of resistance genes was performed using PCR and gel electrophoresis. Results: Out of 398 samples of poultry products, a total of 46 Salmonella isolates were obtained. Most of the isolates belong to the serovar Salmonella Enteritidis (80.4%). The assessment of sensitivity to antibacterial agents showed that Salmonella was mainly resistant to nalidixic acid (63%), furadonin (60.9%), ofloxacin (45.6%), and tetracycline (39.1%). In 64.3% of cases, Salmonella was resistant to three or more groups of antibacterial agents. Resistance genes such as tetA, tetB, blaTEM, aadA, sul3, and catII, as well as integrons of two classes (teg1 and teg2), were identified. Conclusion: Poultry products contain antimicrobial-resistant strains of Salmonella, as well as genes encoding resistance mechanisms. The results emphasize the need for constant monitoring of not only pathogenic microorganisms but also their sensitivity to antimicrobial agents. The potential threat to human health requires a unified approach to the problem of antibiotic resistance from representatives of both public health and the agroindustrial complex. Keywords: antibiotic resistance, food safety, poultry, resistance genes, Salmonella.

The prevalence and characterization of ESBL-producing strains of Salmonella enterica circulating in the territory of the Russian Federation (2016–2020)

Objective. To analyze frequency and identify genetic determinants of resistance of non-typhoid Salmonella (NTS) producing extended-spectrum β-lactamase (ESBL) isolated in the Russian Federation over the period 2016 to 2020. Materials and Methods. Salmonella isolates, suspected to ESBL production, were collected by the All-Russia Reference Center of Salmonellosis during the national Salmonellosis surveillance program. Phenotypic resistance was determined by the broth microdilution method using G-I and G-II Mikrolatest®SensiLaTest MIC plates and by the double-disk synergy test. Whole genome sequencing was performed on the NextSeq platform (Illumina, USA), with subsequent de novo genome assembly (SPAdes 3.15.4), identification of plasmid types (MOB-suite v3.0.0), and identification of resistance genes (AMRFinderPlus v3.10.40). Results. Out of 1792 NTS isolates, 22 strains contained bla-genes of molecular classes A and D (blaTEM, blaCTX-M, blaSHV, blaOXA), one strain – AmpC (blaCMY-2) and three strains – combination ESBL of class A and AmpC (blaTEM, blaCMY-2, blaDHA). The frequency of occurrence of ESBL-producing Salmonella is 1.3%, AmpC – 0.2%. Additionally, strains were resistant to other non-β-lactam antibiotics. Six different types of plasmids were identified (IncI, IncFIB, IncC, IncHI2A, IncL/M and IncX1) in studied isolates. It was possible for 17 strains to identify location of resistance genes in plasmids of a certain type. Conclusions. The frequency of occurrence of Salmonella strains producing ESBL and AmpC was 1.45%, which were found in sporadic cases of human diseases, as well as food and environmental objects were sources of isolation. The fact of detection of such strains among various NTC serotypes and a wide range of sources of isolation confirms the relevance of monitoring antimicrobial resistance of Salmonella strains in the future.

Extended-Spectrum β-Lactamases in Human Isolates of Multidrug-Resistant Non-typhoidal Salmonella enterica

A total of 291 non-duplicate isolates of non-typhoidal Salmonella (NTS) were collected from the fecal samples of patients with salmonellosis in Armenia and Georgia during 1996–2016. The isolates were tested for resistance to antimicrobials, including extended-spectrum β-lactamases (ESBL). The high prevalence of multidrug-resistance (MDR) and ESBL-producer phenotypes was detected among Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) isolates collected from patients in Armenia between 1996 and 2016. A total of 36 MDR NTS isolates were subjected to whole genome sequencing (WGS) to determine the genetic background of antimicrobial resistance (AMR) and mobile genetic elements. All ESBL-producing S. Typhimurium isolates belonged to the same sequence type (ST328). The ESBL-producer phenotype was associated with plasmid-encoded CTX-M-5 production. A range of other plasmids was associated with resistance to other antimicrobials, including the MDR phenotype.

Prevalence of blaCTX-M and Emergence of blaCTX-M-5-Carrying Escherichia coli in Chrysomya megacephala (Diptera: Calliphoridae), Northern Thailand

This study was undertaken to assess the prevalence of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli (ESBL-EC) among blow fly (Chrysomya megacephala) populations in Northern Thailand. Of 600 blow flies collected from rural (n = 400) and urban (n = 200) areas, 334 blow flies carried ESBL-EC (55.7%). Prevalence of ESBL-EC in blow flies captured from rural areas was significantly higher than that from urban region (72.5% vs. 22.0%, p < 0.001). Susceptibility tests revealed that 68.6% of ESBL-EC possessed multidrug-resistant phenotypes. Coresistance to gentamicin (85%) was common, while resistance to ciprofloxacin was relatively low (18.0%). Of the 334 isolates, 253 isolates (75.7%) harbored bla_CTX-M, in which bla_{CTX-M group 1} was predominant (56.5%), followed by bla_{CTX-M group 9} (39.1%). Interestingly, a single isolate was found to carry bla_CTX-M-5, which resided on the IncA/C conjugative plasmid. This is the first report of bla_CTX-M-5 from Thailand and its first identification in blow fly. Pulsed field gel electrophoresis (PFGE) demonstrated high genetic diversity among ESBL-EC isolates. Nevertheless, identical and closely related PFGE profiles were detected among isolates within the same regions and the regions which are several kilometers apart, suggesting that clonal transmission has occurred. Moreover, epidemiologically related isolates were observed between ESBL-EC from blow flies and human intestinal tract. This study provides evidences that blow flies, C. megacephala, are important reservoirs for ESBL-EC and could potentially act as vectors for the spread of ESBL-EC in a Thai community.

The genetic background of antibiotic resistance among clinical uropathogenic Escherichia coli strains

The spreading mechanisms of antibiotic resistance are related to many bacterial and environment factors. The overuse of antibiotics is leading to an unceasing emergence of new multidrug resistant strains. This problem also concerns uropathogenic Escherichia coli strains, which is the most common pathogen causing urinary tract infections. The aim of this study was the genetic analysis of antibiotic resistance in comparison to the phenotypic background of E. coli strains. The characterized collection of E. coli strains isolated 10 years ago from the urine samples of patients with urinary tract infections was used for antimicrobial susceptibility testing (the disc diffusion method) and analysis of antibiotic resistance genes (PCR reaction, sequencing). Additionally, the presence of ESBL strains was analyzed. Fourteen genes were associated with resistance to beta-lactams, aminoglycosides, sulfonamides and quinolones. The genetic analysis revealed that bla_TEM-1 and sul2 were present in almost all of the studied strains. Other drug-resistance genes were very rare or non-existent. Otherwise, the phenotypic resistance to fluoroquinolones was well correlated with the genotypic background of the studied bacteria. The presence of particular genes and specific mutations indicate a high bacterial potential to multidrug resistance. On the other hand, it needs to be emphasized that the standard disk diffusion test for the routine antimicrobial susceptibility analysis is still the best way to estimate the current situation of bacterial drug-resistance.

Complete Genome Sequences of Two Salmonella Viruses, VSe11 and VSe102 (Family Myoviridae, Subfamily Ounavirinae), with a Very High Degree of Similarity

Two lytic double-stranded DNA bacteriophages, VSe11 and VSe102, infecting broad-spectrum Salmonella enterica were isolated from the sewage of two different poultry farms. The phage genomes comprise 86,360 bp and 86,365 bp, respectively, with a G+C content of 39.0%, and both contain 129 putative coding sequences.

DIVERSITY OF ANTIMICROBIAL RESISTANCE MECHANISMS IN SALMONELLA

Abstract. Current review presents information on the antimicrobial resistance of Salmonella of various serotypes. The phenotypes of resistance and the main resistance mechanisms to the antimicrobials of various groups are described. Comparison data on the resistance to antimicrobials of Salmonella serological variants, which circulate worldwide including the Russian Federation (S. Typhimurium DT104, S. Newport, S. Virchow, S. Enteritidis) are shown. Moreover, epidemiological characteristics of transmission factors related to these pathogens are discussed. Special attention is given to genetic determinants, which encode the resistance of Enterobacteriaceae, as well as mobile genetic elements (integrons, plasmids, pathogenicity islands), which are involved in the spread of resistance.

Long-term dissemination of CTX-M-5-producing hypermutable Salmonella enterica serovar typhimurium sequence type 328 strains in Russia, Belarus, and Kazakhstan

In this paper, we present evidence of long-term circulation of cefotaxime-resistant clonally related Salmonella enterica serovar Typhimurium strains over a broad geographic area. The genetic relatedness of 88 isolates collected from multiple outbreaks and sporadic cases of nosocomial salmonellosis in various parts of Russia, Belarus, and Kazakhstan from 1996 to 2009 was established by multilocus tandem-repeat analysis (MLVA) and multilocus sequence typing (MLST). The isolates belong to sequence type 328 (ST328) and produce CTX-M-5 β-lactamase, whose gene is carried by highly related non-self-conjugative but mobilizable plasmids. Resistance to nalidixic acid and low-level resistance to ciprofloxacin is present in 37 (42%) of the isolates and in all cases is determined by various single point mutations in the gyrA gene quinolone resistance-determining region (QRDR). Isolates of the described clonal group exhibit a hypermutable phenotype that probably facilitates independent acquisition of quinolone resistance mutations.

Possibility of CTX-M-14 Gene Transfer from Shigella sonnei to a Commensal Escherichia coli Strain of the Gastroenteritis Microbiome

Objectives

To investigated whether the CTX-M-14 gene could be transferred from a clinical Shigella sonnei strain to commensal Escherichia coli strain in the gastroenteritis microbiome.

Methods

E. coli strains were isolated from 30 stool samples of S. sonnei infected students in a gastroenteritis outbreak in 2004 and were characterized by antibiotic resistance analysis, in vitro conjugation and in vivo transfer of CTX-M-14 gene and molecular assays.

Results

One strain of Escherichia coli that had high levels of resistance to cefotaxime was isolated from a patient infected with S. sonnei. Isoelectric focusing showed that the E. coli and S. sonnei strains produced a β-lactamase with an isoelectric point of 8.1. Moreover, polymerase chain reaction analysis indicated that both strains possessed the same DNA sequences for CTX-M-14. The results of in vitro and in vivo conjugation showed that the efficiency of CTX-M-14 transfer from S. sonnei to E. coli was similar to CTX-M-14 transfer between E. coli strains.

Conclusion

The data suggest that the acquisition of the extended-spectrum β-lactamases gene by pathogenic bacteria in the human intestinal tract to commensal microbiome bacteria can cause serious infectious diseases.

Salmonella enterica serotype Gambia with CTX-M-3 and armA resistance markers: nosocomial infections with a fatal outcome

We report two cases of bacteremia caused by the Salmonella enterica serotype Gambia in our children's hospital, with one fatal outcome. The isolates showed indistinguishable genotypes and infrequent resistance markers: CTX-M-3 extended-spectrum β-lactamase and armA methyltransferase. This is the first report of S. Gambia exhibiting CTX-M-3 and armA markers involved in serious infections.

Extended-spectrum β-lactamase-producing Salmonella enterica serovar Oranienburg (CTX-M-2 group) in a pediatric hospital in Tucumán, Argentina

INTRODUCTION: Salmonella sp infections have been reported over recent years in hospitals in Argentina and other countries due to multiresistant strains. The aim of this study was to characterize the extended-spectrum β-lactamases in third-generation cephalosporin-resistant strains of Salmonella enterica serovar Oranienburg. METHODS: We studied 60 strains isolated from children with gastroenteritis and/or extraintestinal complications. The antibiotic susceptibility patterns of the isolates were analyzed and the β-lactamases were characterized using phenotyping and genotyping methods. RESULTS: All the strains were resistant to ampicillin, cefotaxime, cefepime and aztreonam and partially susceptible to ceftazidime, thus corresponding well with the resistance phenotype conferred by CTX-M-type β-lactamases. An isoelectric point enzyme (pI = 7.9) was detected in all of the strains, and this was confirmed by PCR as a member of the CTX-M-2 group. CONCLUSIONS: This is the first report of Salmonella enterica serovar Oranienburg producing β-lactamases of the CTX-M-2 group in a pediatric hospital in Tucumán, Argentina.

Case report of pediatric gastroenteritis due to CTX-M-15 extended-spectrum beta-lactamase-producing Salmonella enterica serotype enteritidis

A clinical isolate of Salmonella enterica serotype Enteritidis in Korea was found to produce the extended-spectrum beta-lactamase CTX-M-15. The isolate was recovered in 2008 from the stool of a 3-yr-old boy with gastroenteritis. This isolate was found to be resistant to multiple drugs, including ampicillin, piperacillin, cefotaxime, ceftazidime, cefepime, and aztreonam. The resistance to cefotaxime was transferred by conjugation to recipient Escherichia coli J53. The patient was eventually successfully treated with trimethoprim-sulfamethoxazole. This is the first report of the bla (CTX-M-15) gene in S. enterica serotype Enteritidis in Korea.

Emergence of CTX-M-15 type extended-spectrum beta-lactamase-producing Salmonella spp. in Kuwait and the United Arab Emirates

Cephalosporins are major antimicrobials used to treat serious Salmonella infections. However, their effectiveness is being compromised by the emergence of extended-spectrum beta-lactamases (ESBLs). The genetic determinants encoding ESBL in Salmonella spp. isolated from patients in Kuwait and United Arab Emirates (UAE) were studied over a 2 year period. Out of a total of 407 isolates, 116 isolates possessed the resistance phenotypes consistent with possible ESBL production. Of these, 69 (59.5 %) were ESBL positive. PCR and sequencing were used to determine the genetic determinant(s) responsible for ESBL phenotypes. A total of 14 (12.1 %) and 29 (24.6 %) isolates were CTX-M-15 ESBL producers and TEM producers, respectively. Ten CTX-M-15 producers carried the insertion sequence ISEcpI gene. PFGE analysis revealed identical profiles in 4 of the 13 Kuwaiti strains. This study reports the presence of the bla(CTX-M-15) gene in Salmonella spp. and Salmonella enterica serotype Typhi from Kuwait and UAE for what is believed to be the first time. This is of great concern as the gene is also found in association with the ISEcpI gene, which may easily facilitate its spread. These isolates originated mostly from non-Kuwaiti Arabs rather than from people of Asian origin.

Convergent in vivo and in vitro selection of ceftazidime resistance mutations at position 167 of CTX-M-3 beta-lactamase in hypermutable Escherichia coli strains

We report on a novel CTX-M extended-spectrum beta-lactamase (ESBL), designated CTX-M-42, with enhanced activity toward ceftazidime. CTX-M-42 was identified in a hypermutable Escherichia coli nosocomial isolate (isolate Irk2320) and is a Pro167Thr amino acid substitution variant of CTX-M-3. By molecular typing of ESBL-producing E. coli strains previously isolated in the same hospital ward, we were able to identify a putative progenitor (strain Irk1224) of Irk2320, which had a mutator phenotype and harbored the CTX-M-3 beta-lactamase. To reproduce the natural evolution of CTX-M-3, we selected for ceftazidime resistance mutations in bla CTX-M-3 gene in vitro both in clinical isolate Irk1224 and in laboratory-derived hypermutable (mutD5) strain GM2995. These experiments yielded CTX-M-3 Pro167Ser and CTX-M-3 Asn136Lys mutants which conferred higher levels of resistance to ceftazidime than to cefotaxime. CTX-M-3 Asn136Lys had a level of low activity toward ampicillin, which may explain its absence from clinical isolates. We conclude that the selection of CTX-M-42 could have occurred in vivo following treatment with ceftazidime and was likely facilitated by the hypermutable background.

Prevalence and characterization of extended-spectrum cephalosporin-resistant nontyphoidal Salmonella isolates in adults in Saint Petersburg, Russia (2002-2005)

We studied the prevalence of resistance to extended-spectrum cephalosporins (ESC) among 1,078 Salmonella enterica isolates collected from adults admitted to Botkin Hospital, St. Petersburg, Russia, for gastroenteritis between 2002 and 2005. Only two ESC-resistant isolates were detected, giving a low percentage of strains resistant to ESC (0.2%). One multidrug-resistant (MDR) isolate of the Virchow serotype produced a CTXM-3 extended-spectrum beta-lactamase (ESBL). The bla(CTX-M-3) gene was located downstream from an ISEcp1 element, on an 80-kb conjugative plasmid. The Virchow isolate possessed a class 1 integron with a 2.2-kb gene cassette (dhfrXII-orfF-aadA2). The second ESC-resistant isolate belonged to serotype Newport, was also MDR and produced a CMY-2 cephamycinase. This CMY-2-producing isolate (also called Newport MDR-AmpC) possessed a class 1 integron with a 1-kb gene cassette including a new variant of the aadA gene, aadA24. A large plasmid (>125 kb) was involved in transfer of the bla(CMY-2) gene. The ESC-resistant S. enterica isolates detected in this study were different from those (S. enterica serotype Typhimurium DT193 producing CTXM-4 or CTX-M-5 ESBLs) involved in several nosocomial outbreaks between 1994 and 2003 in Russia. This is the first description of both CTX-M-3 ESBL-producing S. enterica and Newport MDR-AmpC in Russia.

Molecular characterisation of multidrug-resistant Salmonella enterica serovar Typhimurium isolates from Gomel region, Belarus

This study describes the characterisation by pulsed-field gel electrophoresis (PFGE), multilocus variable number tandem repeat analysis (MLVA) typing and antimicrobial resistance profiles of 35 Salmonella enterica serovar Typhimurium isolates, mostly from infections in children who acquired an infection outside hospitals in the Gomel region of Belarus. Thirty-one isolates were highly similar according to PFGE and MLVA typing, were multidrug-resistant, including resistance to ceftiofur, and harboured the bla(CTX-M-5) gene. These results indicate that a common source may have been responsible for most of the infections.

Clonal emergence of extended-spectrum beta-lactamase (CTX-M-2)-producing Salmonella enterica serovar Virchow isolates with reduced susceptibilities to ciprofloxacin among poultry and humans in Belgium and France (2000 to 2003)

Antibiotic treatment is not required in cases of Salmonella enterica gastroenteritis but is essential in cases of enteric fever or invasive salmonellosis or in immunocompromised patients. Although fluoroquinolones and extended-spectrum cephalosporins are the drugs of choice to treat invasive Salmonella, resistance to these antibiotics is increasing worldwide. During the period 2000 to 2003, 90 Salmonella enterica serovar Virchow poultry and poultry product isolates and 11 serovar Virchow human isolates were found to produce an extended-spectrum beta-lactamase, CTX-M-2, concomitantly with a TEM-1 beta-lactamase. The bla(CTX-M-2) gene was located on a large conjugative plasmid (>100 kb). Pulsed-field gel electrophoresis indicated a clonal relationship between the poultry and human isolates. All these isolates displayed additional resistance to trimethoprim-sulfamethoxazole and tetracycline as well as a reduced susceptibility to ciprofloxacin (MICs of between 0.5 and 1 mug/ml). CTX-M-2-producing Salmonella with a reduced susceptibility to fluoroquinolones constitutes a major concern, since such strains could disseminate on a large scale and jeopardize classical antibiotic therapy in immunocompromised patients.

Salmonella resistant to extended-spectrum cephalosporins: prevalence and epidemiology

Salmonella resistant to extended-spectrum cephalosporins (ESCs) have emerged worldwide since 1988. By 2004, 43 countries had reported this public health problem. Resistance was mediated by classical extended-spectrum beta-lactamases, plasmid-mediated cephalosporinases, and recently a class A carbapenemase. Of these, CMY-2 is the most widely disseminated enzyme. Salmonella enterica serotype Typhimurium and S. enterica serotype Enteritidis are the most common serovars associated with ESC resistance in human infections. Many outbreaks in humans have been reported, most often among children and neonates. ESC-resistant Salmonella is frequently recovered from animals and food, with poultry as primary food source, suggesting that humans are often infected by these routes.

The first detection of CTX-M-14 extended-spectrum β-lactamase among diverse β-lactamase–producing Proteus mirabilis clinical isolates

CTX-M-14- and -2-like extended-spectrum beta-lactamases were detected in 5 and 1 Proteus mirabilis isolates, respectively, among 92 non-duplicate strains tested from December 2002 to September 2003. This is the first report of the CTX-M-14 enzyme in P. mirabilis to the best of our knowledge and suggests that the CTX-M-type enzyme is gradually spreading to this species. bla(TEM), bla(SHV-1), and/or bla(OXA-10) alleles were also detected in 35 ampicillin-resistant isolates tested.

Analysis of Salmonella spp. with resistance to extended-spectrum cephalosporins and fluoroquinolones isolated in North America and Latin America: report from the SENTRY Antimicrobial Surveillance Program (1997–2004)

Emerging antimicrobial-resistant Salmonella spp. requires increased efforts to appropriately test susceptibility. The SENTRY Antimicrobial Surveillance Program monitored Salmonella spp. and detected nalidixic acid-resistant strains with elevated fluoroquinolone minimum inhibitory concentration (MIC) results and strains with extended-spectrum beta-lactamase (ESBL) "phenotypes" over the last 8 years. A total of 786 stool and bloodstream isolates from North American and Latin American medical centers (2001-2003) were tested by reference broth microdilution methods. Genetic analysis was used to further characterize the resistance mechanisms. Twenty-one sites forwarded 89 (11.3%) nalidixic acid-resistant (MIC, > or =32 microg/mL) strains. Nineteen of these isolates were studied to determine mutations in the quinolone resistance-determining region (QRDR). Among the nalidixic acid-resistant Salmonella spp. isolates, fluoroquinolone MIC values were also elevated (8- to 32-fold) compared with "wild-type" strains. Ciprofloxacin and gatifloxacin (MIC(90), 0.5 microg/mL) were more potent than levofloxacin and garenoxacin (1 microg/mL) against nalidixic acid-resistant strains. Single gyrA mutations were responsible for elevated fluoroquinolone MIC values and included D87Y (5), S83F (7), D87N (5), and S83Y (2). During 2001, 9 sites contributed 11 (2.9%) strains that met ESBL screening criteria (> or =2 microg/mL) for aztreonam or ceftazidime or ceftriaxone. ESBL confirmation was evaluated by Etest (AB BIODISK, Solna, Sweden) ESBL strips and the enzymes were characterized by polymerase chain reaction and gene sequencing. The ESBL phenotype isolates had the following MIC patterns: ceftazidime (> or =16 microg/mL), aztreonam (4 to >16 microg/mL), and ceftriaxone (8-32 microg/mL). All strains were susceptible to cefepime, carbapenems, gentamicin, and fluoroquinolones. No strains were inhibited by clavulanic acid consistent with all isolates producing the identified CMY-2, AmpC-like enzyme. Fluoroquinolones may be compromised among isolates with QRDR mutations detected using nalidixic acid as a screening agent. Salmonella spp. with ESBL phenotypes were likely to harbor CMY-2 (not an ESBL) and remain susceptible to cefepime, carbapenems, and fluoroquinolones, which can be used for serious invasive Salmonella spp. infections. Compared with the stool culture isolates, the blood culture isolates had higher QRDR mutations, but remained susceptible to the fluoroquinolones. The blood culture isolates were more susceptible to penicillins (ampicillin and ticarcillin) and not significantly different for ceftriaxone or trimethoprim/sulfamethoxazole susceptibility patterns. No QRDR trends over time were detected in North America, but increased resistance was observed in Latin America.

Dissemination of CTX-M-type extended-spectrum beta-lactamase genes to unusual hosts

A Citrobacter amalonaticus and a Morganella morganii producing the CTX-M-1 extended-spectrum beta-lactamase (ESBL) were isolated from an area where this enzyme is now widespread in Escherichia coli. This is the first report of CTX-M-1 in the former species. In both cases the ESBL determinant was possibly acquired by these unusual hosts in vivo, after coinfection with E. coli strains carrying conjugative plasmids encoding CTX-M-1.

Nosocomial outbreak of pediatric gastroenteritis caused by CTX-M-14-type extended-spectrum beta-lactamase-producing strains of Salmonella enterica serovar London

CTX-M-14-type extended-spectrum beta-lactamase was first detected in Salmonella enterica serovar London strains which were isolated from three hospitalized pediatric patients with gastroenteritis. The isolates had pulsed-field gel electrophoresis patterns identical to those of the previously isolated antimicrobial-susceptible strains from community-acquired gastroenteritis, suggesting the susceptible clone acquired the resistance.