Survey of extended-spectrum beta-lactamases in clinical isolates of Escherichia coli and Klebsiella pneumoniae: prevalence of TEM-52 in Korea

The Fitness of Beta-Lactamase Mutants Depends Nonlinearly on Resistance Level at Sublethal Antibiotic Concentrations

Adaptive evolutionary processes are constrained by the availability of mutations which cause a fitness benefit and together make up the fitness landscape, which maps genotype space onto fitness under specified conditions. Experimentally derived fitness landscapes have demonstrated a predictability to evolution by identifying limited "mutational routes" that evolution by natural selection may take between low and high-fitness genotypes. However, such studies often utilize indirect measures to determine fitness. We estimated the competitive fitness of mutants relative to all single-mutation neighbors to describe the fitness landscape of three mutations in a β-lactamase enzyme. Fitness assays were performed at sublethal concentrations of the antibiotic cefotaxime in a structured and unstructured environment. In the unstructured environment, the antibiotic selected for higher-resistance types-but with an equivalent fitness for a subset of mutants, despite substantial variation in resistance-resulting in a stratified fitness landscape. In contrast, in a structured environment with a low antibiotic concentration, antibiotic-susceptible genotypes had a relative fitness advantage, which was associated with antibiotic-induced filamentation. These results cast doubt that highly resistant genotypes have a unique selective advantage in environments with subinhibitory concentrations of antibiotics and demonstrate that direct fitness measures are required for meaningful predictions of the accessibility of evolutionary routes. IMPORTANCE The evolution of antibiotic-resistant bacterial populations underpins the ongoing antibiotic resistance crisis. We aim to understand how antibiotic-degrading enzymes can evolve to cause increased resistance, how this process is constrained, and whether it can be predictable. To this end, competition experiments were performed with a combinatorially complete set of mutants of a β-lactamase gene subject to subinhibitory concentrations of the antibiotic cefotaxime. While some mutations confer on their hosts high resistance to cefotaxime, in competition these mutations do not always confer a selective advantage. Specifically, high-resistance mutants had equivalent fitnesses despite different resistance levels and even had selective disadvantages under conditions involving spatial structure. Together, our findings suggest that the relationship between resistance level and fitness at subinhibitory concentrations is complex; predicting the evolution of antibiotic resistance requires knowledge of the conditions that select for resistant genotypes and the selective advantage evolved types have over their predecessors.

Growing threat of extended-spectrum β-lactamase-producing Enterobacteriaceae colonisation in high-risk pregnancies: A cross-sectional study

OBJECTIVE

To investigate the epidemiological changes in extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-E) vaginal colonisation in pregnant women deemed at high risk, and to identify independent risk factors. Further, the differences in perinatal outcomes according to maternal ESBL-E vaginal colonisation were analysed.

DESIGN

Cross-sectional study.

SETTING

Republic of Korea.

POPULATION

A cohort of 1460 women admitted to our high-risk pregnancy unit between 14⁺⁰ and 36⁺⁶  weeks of gestation.

METHODS

The trend of changes in the association of ESBL-E vaginal colonisation from January 2010 to December 2020 was analysed. The main outcomes were analysed over the study period and ESBL-E vaginal colonisation.

MAIN OUTCOME MEASURES

Rate of ESBL-E vaginal colonisation, risk factors for ESBL-E vaginal colonisation and perinatal outcomes.

RESULTS

The ESBL-E vaginal colonisation rate has tended to increase over the past 11 years, which was attributed to a significantly higher proportion of ESBL-producing Escherichia coli. Cerclage (RR 3.7, 95% CI 2.19-6.40) and prior antibiotic treatment (RR 4.0, 95% CI 2.44-6.54) were found as independent risk factors for ESBL-E vaginal colonisation. Earlier gestational age at delivery and higher proven early-onset neonatal sepsis (EONS) rate were observed in the ESBL-E-positive group.

CONCLUSIONS

The ESBL-E vaginal colonisation rate in pregnant patients at high risk has increased over the past decade, and the independent risk factors for colonisation are cerclage and prior antibiotic treatment. Additionally, maternal ESBL-E vaginal colonisation is associated with higher rates of proven EONS.

Detection of Beta-Lactamases (ESBL and MBL) Producing Gram-Negative Pathogens in National Public Health Laboratory of Nepal

Background

Bacterial resistance to antibiotics has increased in recent years. Resistance to β-lactams in Gram-negative bacteria has been reported to be associated with extended spectrum beta-lactamases and metallo-beta-lactamases. This study was aimed at determining the distribution and antibiotic susceptibility patterns of Gram-negative pathogens producing extended spectrum beta lactamases and metallo-beta lactamases. Method and Methodology. This cross-sectional study was conducted at the National Public Health Laboratory during a period of six months. All clinical specimens were obtained and processed for the identification of Gram-negative pathogens by culture, morphological, and biochemical tests. Antibiotic susceptibility testing of the isolates was performed by the Kirby Bauer disc diffusion and the isolates were tested for ESBL and MBL by the combined disk method.

Results

Out of 4266 clinical specimens, 197 (4.6%) were found to be Gram-negative bacterial isolates. 47 (23.9%) isolates were ESBL producers. The most predominant organisms were Escherichia coli (53%), Klebsiella pneumonia (23%), and Pseudomonas spp. (13%). 16 (8.2%) were positive for MBL producers, and 6(3.1%) were both ESBL and MBL producers. The MBL activity was seen in E. coli (38%), followed by Pseudomonas spp. (31%), and K. pneumoniae (19%). The ESBL producers showed a higher degree of sensitivity towards imipenem and amikacin, followed by piperacillin tazobactam. MBL producers showed sensitivity towards amikacin only.

Conclusion

The prevalence of ESBL and MBL producing Gram-negative bacteria was found to be high in bacterial infections in Nepal. Routine laboratory testing for ESBL and MBL is needed in order to optimize antibiotic management and reduce the risk of spread of infections caused by ESBL and MBL producers.

Serotypes, Antibiotic Resistance Genes, and Salmonella Pathogenicity Island Genes of Salmonella from Patients in a Hospital in Weifang, China

Background: Salmonella is an important foodborne pathogen that causes diarrhea in humans worldwide. Objectives: This study aimed to determine the serotype distribution, antibiotic-resistant genes, and Salmonella pathogenicity island (SPI) genes of clinical isolates of Salmonella in Weifang. Methods: A total of 111 Salmonella strains were collected from Weifang People’s Hospital between 2018 and 2020 and subjected to serotyping using the Kauffmann-White antigen table. Meanwhile, the polymerase chain reaction detected eleven SPI1-6 genes and six antibiotic resistance genes. Results: Among the 111 Salmonella strains, 17 serotypes were identified, with S. Typhimurium, S. Typhi, and S. Enteritidis being the most prevalent. The hilA, ssaB, sseC, marT, siiE, pipB, sopB, and pagN SPI1-6 genes were all found during analysis. The InvA, misL, and siiD genes were detected at 98.2, 97.30, and 97.30% rates, respectively. Also, sul2 and blaTEM were the most prevalent antibiotic resistance genes in this investigation, accounting for 68.47 and 21.62% of the total, respectively. Conclusions: Salmonella isolated from the clinical samples was found to have a diversity of serotypes and possessed various SPI and antibiotic resistance genes.

TEM,CTX-M,SHV Genes in ESBL-Producing Escherichia coli and Klebsiella pneumoniae Isolated from Clinical Samples in a County Clinical Emergency Hospital Romania-Predominance of CTX-M-15

Background: CTX-M betalactamases have shown a rapid spread in the recent years among Enterobacteriaceae and have become the most prevalent Extended Spectrum Beta-Lactamases (ESBLs) in many parts of the world. The introduction and dissemination of antibiotic-resistant genes limits options for treatment, increases mortality and morbidity in patients, and leads to longer hospitalization and expensive costs. We aimed to identify the beta-lactamases circulating encoded by the genes bla_CTX-M-15, bla_SHV-1 and bla_TEM-1 in Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) strains. Furthermore, we established the associated resistance phenotypes among patients hospitalized in the Intensive Care Unit (ICU) from County Clinical Emergency Hospital of Craiova, Romania. Methods: A total of 46 non-duplicated bacterial strains (14 strains of E. coli and 32 strains of K. pneumoniae), which were resistant to ceftazidime (CAZ) and cefotaxime (CTX) by Kirby–Bauer disk diffusion method, were identified using the automated VITEK2 system. Detection of ESBL-encoding genes and other resistance genes was carried out by PCR. Results. E. coli strains were resistant to 3rd generation cephalosporins and moderately resistant to quinolones, whereas K. pneumoniae strains were resistant to penicillins, cephalosporins, and sulfamides, and moderately resistant to quinolones and carbapenems. Most E. coli strains harbored bla_CTX-M-15 gene (13/14 strains), a single strain had the bla_SHV-1 gene, but 11 strains harbored bla_TEM-1 gene. The mcr-1 gene was not detected. We detected tet(A) gene in six strains and tet(B) in one strain. In K. pneumoniae strains we detected bla_CTX-M-15 in 23 strains, bla_SHV-₁ in all strains and bla_TEM-1 in 14 strains. The colistin resistance gene mcr-1 was not detected. The tetracycline gene tet(A) was detected in 11 strains, but the gene tet(B) was not detected in any strains. Conclusions. The development in antibiotic resistance highlights the importance of establishing policies to reduce antibiotic use and improving the national resistance surveillance system in order to create local antibiotic therapy guidelines.

Prevalence of extended-spectrum β-lactamase (ESBL) and molecular detection of blaTEM, blaSHV and blaCTX-M genotypes among Enterobacteriaceae isolates from patients in Khartoum, Sudan

Introduction

the emergence of antibiotic resistance pathogens is an important health risk. Usually Gram negative bacteria acquire resistance to beta-lactam antibiotics by beta-lactamase production. The objectives of this study was to assess the prevalence of ESBL and to detect the frequency of blaTEM, blaSHV and blaCTX-M genotypes among ESBL producing Enterobacteriaceae isolates from patients in Khartoum, Sudan.

Methods

a total of 171 isolates of Enterobacteriaceae were recovered from hospitals in Khartoum, Sudan (2014 -2015) were used to detect ESBL production using disc diffusion method. blaTEM, blaSHV and blaCTX-M genes were investigated by PCR based methods using gene-specific primers.

Results

the high resistance among Enterobacteriaceae was noticed in ciprofloxacin (72%) and ofloxacin (73%). ESBL production was mainly in Escherichia Coli (38%) and Klebsiella pneumonia (34%). Prevalent genotypes were blaTEM (86%), blaCTX-M (78%) and blaSHV (28%). These were found mainly in Escherichia Coli (38%, 37%, 2%) and K. pneumonia (34%, 31%, 26.1%). The majority of ESBL producing isolates possess more than one ESBL genes.

Conclusion

the ESBL production in Enterobacteriaceae was high, with blaTEM and blaCTX-M genotypes more prevalent. Public health and laboratory standard of excellence is needed to reducing the spread of resistant pathogens.

The Emergence of Klebsiella pneumoniae with Reduced Susceptibility Against Third Generation Cephalosporins and Carbapenems in Lagos Hospitals, Nigeria

This study investigated the prevalence of Klebsiella (K.) pneumoniae isolates among clinical samples of patients in four medical centers in Lagos, Nigeria and the burden of extended-spectrum beta-lactamases (ESBL) and carbapenem-resistant K. pneumoniae (CRKP) strains. Different samples (stool, blood, urine, wound swabs and nasal swabs) from 127 patients with suspected Gram-negative infections based on on-site performed Gram-stain from four public hospitals between March and September 2015 were analyzed. K. pneumoniae was identified in 43 (34%) patients. Resistance rates of these 43 strains according to the CLSI breakpoints were as followed: cotrimoxazole (90.7%), cefuroxime (74.4%), ofloxacin (55.8%), ceftazidime (46.5%), and cefixime (35%). Three isolates (7%) were resistant to imipenem. All isolates were susceptible to amoxicillin/clavulanic acid and nitrofurantoin. The prevalence of ESBL-producing, MDR and CRKP strains was 69.8%, 62.8%, and 7.0%, respectively. Of the ESBL-producing isolates, two K. pneumoniae isolates obtained from urine harbored both bla_SHV and bla_CTX-M-1, and a third isolate from urine harbored only the bla_CTX-M-1. This study revealed the emergence of CRKP isolates and bla_CTX-M-1 and bla_SHV co-harboring K. pneumoniae strains in Lagos hospitals. The emergence of CRKP strains is an early warning signal for carbapenem antibiotics’ prudent use with concern for their efficacies.

Exploitation of Antibiotic Resistance as a Novel Drug Target: Development of a β-Lactamase-Activated Antibacterial Prodrug

Expression of β-lactamase is the single most prevalent determinant of antibiotic resistance, rendering bacteria resistant to β-lactam antibiotics. In this article, we describe the development of an antibiotic prodrug that combines ciprofloxacin with a β-lactamase-cleavable motif. The prodrug is only bactericidal after activation by β-lactamase. Bactericidal activity comparable to ciprofloxacin is demonstrated against clinically relevant E. coli isolates expressing diverse β-lactamases; bactericidal activity was not observed in strains without β-lactamase. These findings demonstrate that it is possible to exploit antibiotic resistance to selectively target β-lactamase-producing bacteria using our prodrug approach, without adversely affecting bacteria that do not produce β-lactamase. This paves the way for selective targeting of drug-resistant pathogens without disrupting or selecting for resistance within the microbiota, reducing the rate of secondary infections and subsequent antibiotic use.

Profiling of antimicrobial resistance and plasmid replicon types in β-lactamase producing Escherichia coli isolated from Korean beef cattle

In this study, 78 isolates of Escherichia coli isolated from Korean beef cattle farms were investigated for the production of extended-spectrum β-lactamase (ESBL) and/or AmpC β-lactamase. In the disc diffusion test with ampicillin, amoxicillin, cephalothin, ceftiofur, cefotaxime, ceftazidime, and cefoxitin, 38.5% of the isolates showed resistance to all of ampicillin, amoxicillin, and cephalothin. The double disc synergy method revealed that none of the isolates produced ESBL or AmpC β-lactamases. DNA sequencing showed that all isolates encoded genes for TEM-1-type β-lactamase. Moreover, 78.2% of the isolates transferred the TEM-1-type β-lactamase gene via conjugation. In plasmid replicon typing of all donors, IncFIB and IncFIA were identified in 71.4% and 41.0% of plasmids, respectively. In transconjugants, IncFIB and IncFIA were the most frequent types detected (61.5% and 41.0%, respectively). Overall, the present study indicates that selection pressures of antimicrobials on β-lactamases in beef cattle may be low relative to other livestock animals in Korea. Moreover, to reduce selection pressure and dissemination of β-lactamase, the long-term surveillance of antimicrobial use in domestic beef cattle should be established.

Characterization of IS26-composite transposons and multidrug resistance in conjugative plasmids from Enterobacter cloacae

SHV-12 is the most widespread resistance determinant of Enterobacter cloacae in Taiwan; however, blaSHV-12 has rarely been mobilized. Six multidrug-resistant E. cloacae isolates were collected. After conjugal transfer, plasmid profiling and analysis of incompatibility groups was performed to characterize the genetic context of blaSHV-12 -containing fragments. The presence of mobile genetic elements was demonstrated by PCR, cloning, sequencing and bioinformatics analyses. Four different β-lactamase genes (blaTEM-1 , blaSHV-12 , blaCTX-M-3 and/or blaCTX-M-14 ) were observed in the conjugative plasmids belonging to the IncHI2 (n = 4), IncI1 or IncP incompatibility groups. The IS26-blaSHV-12 -IS26 locus was located in five different genetic environments. A novel structural organization of a class 1 integron with the aac(6')-IIc cassette truncated by IS26 was identified in one isolate. Thus, blaSHV-12 was obtained from different plasmids through IS26-mediated homologous recombination. IS26 plays a vital role in the distribution of mobile resistance elements between different plasmids found in multidrug-resistant E. cloacae isolates.

Etiology and antibiotic susceptibility of bacterial pathogens responsible for community-acquired urinary tract infections in Poland

Urinary tract infections (UTIs) are some of the most common infections in both community and hospital settings infections. With their high rate of incidence, recurrence, complications, diverse etiologic agents, as well as growing antibiotic resistance, UTIs have proven to be a serious challenge for medical professionals. The aim of this study was to obtain data on the susceptibility patterns of pathogens responsible for UTIs in Poland to currently used antibiotics. A total of 396 bacterial isolates were collected between March and May 2013 from 41 centers in all regions of Poland. The majority of isolates were from adult patients (96.2 %); 144 (37.8 %) patients were diagnosed with uncomplicated UTI, while the remaining 237 (62.2 %) had a complicated infection. The most prevalent pathogen was Escherichia coli (71.4 %), followed by Klebsiella spp. (10.8 %) and the Proteae group (7.6 %). Escherichia coli was responsible for 80.6 % of cases of uncomplicated and 65.8 % of complicated infections. Only 65.8 % of E. coli isolates were susceptible to ciprofloxacin (uncomplicated 75.9 %, complicated 58.3 %), 64.0 % to nitrofurantoin (67.2 %, 62.8 %), 65.1 % to trimethoprim/sulfamethoxazole (68.1 %, 62.8 %), and 66.4 % to fosfomycin (77.6 %, 62.2 %). Among E. coli isolates from all UTIs, only 43.4 % were susceptible to ampicillin, with 47.4 % from uncomplicated compared with 40.4 % from complicated infections; 88.2 % to amoxicillin/clavulanic acid (91.4 % vs. 85.9 % complicated); 90.1 % to cefuroxime (93.1 %, 87.8 %); and 94.1 % to cefotaxime (98.2 %, 91.0 %). Thirty-five strains (10.4 %) were capable of producing extended-spectrum β-lactamases (ESBLs). This study demonstrates an increase in multidrug-resistant strains, especially among the leading pathogens associated with UTIs, including E. coli, Klebsiella spp., and Proteus spp.

Antimicrobial resistance and integron profiles in multidrug-resistant Escherichia coli isolates from pigs

From July 2006 to June 2008, a total of 3876 Escherichia coli strains were collected from 1014 porcine intestinal contents to investigate antimicrobial resistance and related gene patterns. Average resistance rates of porcine E. coli isolates were 93.2% for tetracycline, 65.3% for ampicillin, 60.4% for chloramphenicol, 57.7% for streptomycin, 35.8% for nalidixic acid, 23.6% for gentamicin, 10.8% for ciprofloxacin, 10.0% for norfloxacin, 4.5% for cephalothin, 1.0% for cefoxitin, and 0.4% for cefazolin. The number of isolates resistant to more than 3 different classes of antimicrobials was 2537. Among these, 92 isolates were resistant to 5 or more classes of antimicrobials, and 69 isolates among 92 multidrug-resistant (MDR) isolates were integrase positive. Among 69 integrase-positive MDR isolates, only class I integron was detected in 19 isolates (20.7%). The class-1-integron-positive isolates had different sizes and gene contents (i.e., 1.0 kb containing aadA1 and 1.5 kb containing aadA1-dfrA1 and aadA1-aadB), and showed 15 distinct types by pulsed-field gel electrophoresis (PFGE) analysis, with 80% cut-off band pattern similarity. PFGE typing of four groups of isolates with identical antimicrobial resistance gene profiles showed two heterogeneous groups, while one group had very similar PFGE patterns; the fourth group was not typeable due to DNA degradation. In conjugation experiments, class I integron-harboring isolates transferred resistance to ampicillin, norfloxacin, gentamicin, and chloramphenicol to the recipient strain. This study showed that antimicrobial resistance rates and corresponding genes in porcine E. coli isolates are different from those in human isolates described by previous studies, and that transfer of antimicrobial-resistant genes from animal to human occurred. These data can be used as a baseline to evaluate the effect of antimicrobial use after implementation of the animal antimicrobial ban for prophylactic and growth promotion except for therapeutic use in 2012 in Korea.

Improved detection of extended spectrum beta-lactamase (ESBL)-producing Escherichia coli in input and output samples of German biogas plants by a selective pre-enrichment procedure

The presence of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli was investigated in input (manure from livestock husbandry) and output samples of six German biogas plants in 2012 (one sampling per biogas plant) and two German biogas plants investigated in an annual cycle four times in 2013/2014. ESBL-producing Escherichia coli were cultured by direct plating on CHROMagar ESBL from input samples in the range of 10⁰ to 10⁴ colony forming units (CFU) per g dry weight but not from output sample. This initially indicated a complete elimination of ESBL-producing E. coli by the biogas plant process. Detected non target bacteria were assigned to the genera Acinetobacter, Pseudomonas, Bordetella, Achromobacter, Castellaniella, and Ochrobactrum. A selective pre-enrichment procedure increased the detection efficiency of ESBL-producing E. coli in input samples and enabled the detection in five of eight analyzed output samples. In total 119 ESBL-producing E. coli were isolated from input and 46 from output samples. Most of the E. coli isolates carried CTX-M-type and/or TEM-type beta lactamases (94%), few SHV-type beta lactamase (6%). Sixty-four bla_CTX-M genes were characterized more detailed and assigned mainly to CTX-M-groups 1 (85%) and 9 (13%), and one to group 2. Phylogenetic grouping of 80 E. coli isolates showed that most were assigned to group A (71%) and B1 (27%), only one to group D (2%). Genomic fingerprinting and multilocus sequence typing (MLST) showed a high clonal diversity with 41 BOX-types and 19 ST-types. The two most common ST-types were ST410 and ST1210. Antimicrobial susceptibility testing of 46 selected ESBL-producing E. coli revealed that several isolates were additionally resistant to other veterinary relevant antibiotics and some grew on CHROMagar STEC but shiga-like toxine (SLT) genes were not detected. Resistance to carbapenems was not detected. In summary the study showed for the first time the presence of ESBL-producing E. coli in output samples of German biogas plants.

Antimicrobial Susceptibility Profile of Extended Spectrum β-Lactamase (ESBL) Producing Escherichia coli from Various Clinical Samples

BACKGROUND

Extended spectrum β-lactamase (ESBL) producing Escherichia coli has tremendously increased worldwide and it is one of the most common causes of morbidity and mortality associated with hospital-acquired infections. This could be attributed to association of multi drug resistance in ESBL producing isolates. The present study was aimed to determine the antimicrobial sensitivity profile of ESBL producing E. coli isolates from various clinical samples.

MATERIALS AND METHODS

Clinical samples, which consist of pus, urine, blood, cerebrospinal fluid (CSF), stool, sputum, swabs, and different body fluids, are included in the study. Samples were processed and identified as per routine laboratory protocol. ESBL screening and confirmation along with antimicrobial susceptibility test was done according to the Clinical Laboratory Standards Institute (CLSI) guidelines.

RESULTS

Out of 180 third generation cephalosporins resistant E. coli, 100 (55.55%) isolates were ESBL producers showing a greater degree of resistance to antibiotics.

CONCLUSION

The prevalence of ESBL is increasing day by day in nearly every center of different countries and necessary steps to prevent the spread and emergence of resistance should be taken.

Molecular analysis of a prolonged spread of Klebsiella pneumoniae co-producing DHA-1 and SHV-12 β-lactamases

The study investigated molecular mechanisms for prolonged nosocomial spread of multidrug-resistant Klebsiella pneumoniae co-producing plasmid-mediated AmpC β-lactamase DHA-1 and extended-spectrum β-lactamase SHV-12. Forty-eight clinical isolates of K. pneumonia, resistant to the extended-spectrum cepha-losporins, were collected in a 750-bed university hospital over a year. The isolates were characterized for PCR-based β-lactamase genotypes, isoelectric focusing and pulsed-field gel electrophoresis (PFGE) profiles. Resistance transfer was performed by plasmid conjugation and confirmed by a duplex-PCR and Southern hybridization. On β-lactamase typing, the strains producing only the DHA-1 enzyme (n=17) or co-producing DHA-1 and SHV-12 enzymes (n=15) were predominant. Judging from a one year-distribution of PFGE profiles, the co-producer was spread primarily with single clonal expansion of the PFGE-type A with subtypes (n=14), whereas the strains producing only DHA-1 enzyme were spread simultaneously with the PFGE-type A (n=ll) and other PFGE types (n=6). Transconjugants of the co-producers were confirmed to harbor either both bla (DHA-1) and bla (SHV-12) or only the bla (DHA-1). In conclusion, this study indicated that the persistent nosocomial spread of multidrug-resistant K. pneumoniae strains was primarily associated with expansion of a clone harboring both the bla (DHA-1) and bla (SHV-12) or the bla (DHA-1) only, and to a lesser extent with the horizontal transfer of the resistant plasmids. Our observations have clinical implication for the control and prevention of nosocomial dissemination of multidrug-resistant K. pneumoniae strains.

Antibiotic resistance patterns and detection of blaDHA-1 in Salmonella species isolates from chicken farms in South Korea

Fifteen nonrepetitive ampicillin-resistant Salmonella spp. were identified among 91 Salmonella sp. isolates during nationwide surveillance of Salmonella in waste from 131 chicken farms during 2006 and 2007. Additional phenotyping and genetic characterization of these 15 isolates by using indicator cephalosporins demonstrated that resistance to ampicillin and reduced susceptibility to cefoxitin in three isolates was caused by TEM-1 and DHA-1 beta-lactamases. Plasmid profiling and Southern blot analysis of these three DHA-1-positive Salmonella serovar Indiana isolates and previously reported unrelated clinical isolates of DHA-1-positive Salmonella serovar Montevideo, Klebsiella pneumoniae, and Escherichia coli from humans and swine indicated the involvement of the large-size plasmid. Restriction enzyme digestion of the plasmids from the transconjugants showed variable restriction patterns except for the two Salmonella serovar Indiana isolates identified in this study. To the best of our knowledge, this is the first report of the presence of the DHA-1 gene among Salmonella spp. of animal origin.

Extended Spectrum beta-Lactamases among Gram-Negative Bacterial Isolates from Clinical Specimens in Three Major Hospitals in Northern Jordan

Background and Objectives. Extended spectrum β-lactamase (ESBL) production is increasing all over the world, and organisms other than E. coli and K. pneumoniae are acquiring this character. ESBL production is detectable by automation, E-test, double disk diffusion (DDD), and PCR. This study aimed to determine the prevalence of ESBL production among clinical isolates of gram-negative rods, and to evaluate the effectiveness of augmentation of clavunate with Cefotaxime, Ceftazoxime, Aztreonam, Ceftriaxone, and Cefpodoxime in detecting ESBL production. Methods. 472 clinical gram-negative isolates identified by standard methods were tested for ESBL-production by (DDD) method using six cephalosporins and amoxicillin-clavulinate discs. Results. 108/472 (22.9%) of the isolates were ESBL producers, and were prevalent in tertiary care hospitals. 88.2% of E. cloacae, 71.4% of K. pneumoniae, 28.6% of K. oxytoca, 12.5% of C. freundii, 11.1% of A. calcoacceticus, and 10.8% of E. coli were ESBL producers. The DDD test demonstrated some variations in the efficacy of the different cephalosporins in detecting all the ESBL producers. The inclusion of ceftizoxime discs increased the efficacy of the test. It is concluded that ESBL-producing bacteria were prevalent among our hospitalized patients, and involved genera other than Klebsiella and Escherichia, and the inclusion of ceftizoxime increased the efficacy of ESBL detection by the DDD test.

Spread of CTX-M-type extended-spectrum beta-lactamases among bloodstream isolates of Escherichia coli and Klebsiella pneumoniae from a Korean hospital

This study was to determine the prevalence and characteristics of CTX-M-type extended-spectrum beta-lactamases (ESBLs) in nonduplicate Escherichia coli (n=760) and Klebsiella pneumoniae (n=379) bloodstream isolates collected during January 2005 to October 2007 at a university hospital (2000 beds) in Seoul, Korea. Antimicrobial susceptibilities were determined by disk diffusion and agar dilution methods. The double-disk synergy test detected ESBLs in 8.7% (66/760) of E. coli and 11.3% (43/379) of K. pneumoniae isolates. Polymerase chain reaction detected bla(CTX-M) in 60/66 (90.9%) E. coli and 9/43 (20.9%) K. pneumoniae isolates with the ESBL phenotype. CTX-M-14 was the most common type of CTX-M ESBLs in both E. coli (n=32) and K. pneumoniae (n=6). CTX-M-15 was the 2nd most common type of CTX-M ESBLs in E. coli (n=22), but it was not detected in K. pneumoniae. In addition, CTX-M-24 (n=2), CTX-M-65 (n=2), CTX-M-27 (n=1), and CTX-M-32 (n=1) were detected for the 1st time in Korea.

Phenotypic characterization of human pathogenic bacteria in fish from the coastal waters of South West Cameroon: public health implications

Increasing economic and recreational opportunities, attractive scenery and a perception of a better quality of life are luring people to the coast. Unfortunately, these activities together with the commensurate increase in population in the area inevitably result in pollution of coastal waters with excessive microorganisms and other pollutants. Microbial pollutants not only contaminate the coastal water but also aquatic food sources, thus posing a health risk to consumers. Fish is a major source of protein in Cameroon, especially in the coastal areas. In this study, we investigated the microbiological quality of fish from the Limbe and Tiko beaches in South West Cameroon from May to October 2007. We isolated human pathogenic bacteria from three anatomic sites (skin, gills, intestine) of 50 fish (150 specimens) and investigated their susceptibility patterns to a battery of antibiotics. Data were analyzed statistically using chi2 with significance set at p < .05. Eleven bacterial species were identified, including Escherichia coli type 1 (20.8%), Citrobacter fruendii (16.4%), Proteus vulgaris (13%), Klebsiella pneumoniae (12.1%), Klebsiella ozaenae (7.7%), Enterobacter cloacae (7.2%), Klebsiella oxytoca (5.8%), Serratia marcescens (4.8%), Serratia odorifera (4.8%), Hafnia alvei (4.4%) and Proteus penneri (2.9%). More contaminated fish were found at Limbe beach than at Tiko beach (61.4% versus 38.6%, respectively (p < .05)). When ranking contamination with respect to anatomic site, skin was the most contaminated (40.6%) specimen and gills the least (28.5%). Ciprofloxacillin, ofloxacillin, and cotrimoxazole were the most effective antibiotics against all isolates, exhibiting 100% sensitivity. Almost half of the isolates (45.7%) were resistant to ampicillin. The results of our study demonstrate that fish from the coastal waters of South West Cameroon are a source of human pathogenic and opportunistic bacteria; hence this finding has public health implications.

Risk factors and clinical features of infections caused by plasmid-mediated AmpC beta-lactamase-producing Enterobacteriaceae

A case-control study was performed with the objective of analysing risk factors and clinical features of infections caused by plasmid-mediated AmpC beta-lactamase (plasmid AmpC)-producing Enterobacteriaceae. All patients infected with plasmid AmpC-producing Enterobacteriaceae in two tertiary care hospitals from December 2006 to August 2007 were included. Plasmid AmpC enzymes were characterised by isoelectric focusing, enzyme inhibition assay and enzyme-specific polymerase chain reaction. A total of 30 patients (20 with Klebsiella pneumoniae and 10 with Escherichia coli) were recruited prospectively. CMY-2 and DHA-1 were the most common plasmid AmpC in E. coli and K. pneumoniae, respectively. An independent risk factor for infection with plasmid AmpC-producing Enterobacteriaceae was the use of an oxyimino-cephalosporin within 1 month of plasmid AmpC infection [adjusted odds ratio (aOR), 10.8, 95% confidence interval (CI), 1.6-75.4; P=0.016], with the use of a urinary catheter showing borderline significance (aOR, 6, 95% CI 0.93-38.4; P=0.06). An independent risk factor for treatment failure at 72 h was infection due to plasmid AmpC-producing Enterobacteriaceae (aOR, 9.78, 95% CI 1.34-71.17; P=0.02). These results suggest that infections caused by plasmid AmpC-producing isolates significantly increase treatment failure at 72 h and that prior use of an oxyimino-cephalosporin is a risk factor for infections caused by plasmid AmpC-producing Enterobacteriaceae.

CTX-M-14 and CTX-M-15 enzymes are the dominant type of extended-spectrum beta-lactamase in clinical isolates of Escherichia coli from Korea

This study was performed to assess the prevalence and genotypes of plasmid-borne extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases in Escherichia coli in Korea. A total of 576 isolates of E. coli was collected from 12 Korean hospitals during May and July 2007. A phenotypic confirmatory test detected ESBLs in 82 (14.2 %) of the 576 E. coli isolates. The most common types of ESBLs identified were CTX-M-14 (n=32) and CTX-M-15 (n=27). The prevalence and diversity of the CTX-M mutants, including CTX-M-15, CTX-M-27 and CTX-M-57, with significant hydrolytic activity against ceftazidime were increased. PCR experiments detected genes encoding plasmid-borne AmpC β-lactamases in 15/56 cefoxitin-intermediate or cefoxitin-resistant isolates, and the most common type of AmpC β-lactamase identified was DHA-1 (n=10). These data suggest that the incidence of ESBLs in E. coli has increased as a result of the dissemination of CTX-M enzymes in Korea. In addition, CTX-M-22, CTX-M-27 and CTX-M-57 have appeared in Korea.

Characterization of conjugative plasmids carrying antibiotic resistance genes encoding 16S rRNA methylase, extended-spectrum beta-lactamase, and/or plasmid-mediated AmpC beta-lactamase

In this study, we identified extended-spectrum beta-lactamase (ESBL) and plasmid-mediated AmpC beta-lactamase which were associated with 16S rRNA methylase gene on the conjugative plasmid. Among 82 clinical isolates of Enterobacteriaceae that carry 16S rRNA methylase gene (64 strains, armA, and 18 strains, rmtB), bla(SHV-12) was detected either alone or combined with bla(DHA-1), bla(CTX-M-3), and bla(CTX-M-14) in 30 strains carrying armA and 6 strains carrying rmtB. The bla(CTX-M-3) was detected in 13 of 64 strains carrying armA but no strains carrying rmtB. Whereas bla(CTX-M-14) was detected in 15 of 18 strains carrying rmtB but only 2 of 64 strains carrying armA. Overall, bla(SHV-12) and bla(CTX-M-14) was the most common ESBL gene which was associated with armA and rmtB, respectively. In addition, we found that bla(CTX-M-3) localized with armA on the same IncL/M plasmid and bla(CTX-M-14) localized with rmtB on the same IncA/C plasmid. Restriction fragment length polymorphism of conjugative plasmids and pulsed-field gel electrophoresis of genomic DNAs revealed that intercellular horizontal transfer of conjugative plasmid and clonal transmission have been occurred at the same time.

Molecular characterization and epidemiology of extended-spectrum-beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolates causing health care-associated infection in Thailand, where the CTX-M family is endemic

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae have rapidly spread worldwide and pose a serious threat for health care-associated (HA) infection. We conducted molecular detection and characterization of ESBL-related bla genes, including bla(TEM), bla(SHV), bla(CTX-M), bla(VEB), bla(OXA), bla(PER), and bla(GES), among 362 isolates of ESBL-producing E. coli (n = 235) and ESBL-producing K. pneumoniae (n = 127) collected from patients who met the definition of HA infection at two major university hospitals in Thailand from December 2004 to May 2005. The prevalence of ESBL-producing E. coli and ESBL-producing K. pneumoniae, patient demographics and the susceptibilities of these bacteria to various antimicrobial agents were described. A total of 87.3% of isolates carried several bla genes. The prevalence of bla(CTX-M) was strikingly high: 99.6% for ESBL-producing E. coli (CTX-M-14, -15, -27, -40, and -55) and 99.2% for ESBL-producing K. pneumoniae (CTX-M-3, -14, -15, -27, and -55). ISEcp1 was found in the upstream region of bla(CTX-M) in most isolates. Up to 77.0% and 71.7% of ESBL-producing E. coli and ESBL-producing K. pneumoniae, respectively, carried bla(TEM); all of them encoded TEM-1. ESBL-producing K. pneumoniae carried bla(SHV) at 87.4% (SHV-1, -2a, -11, -12, -27, -71, and -75) but only at 3.8% for ESBL-producing E. coli (SHV-11 and -12). bla genes encoding VEB-1 and OXA-10 were found in both ESBL-producing E. coli (8.5% and 8.1%, respectively) and ESBL-producing K. pneumoniae (10.2% and 11.8%, respectively). None of the isolates were positive for bla(PER) and bla(GES). Pulsed-field gel electrophoresis analysis demonstrated that there was no major clonal relationship among these ESBL producers. This is the first study to report CTX-M-3, CTX-M-27, CTX-M-40, SHV-27, SHV-71, and SHV-75 in Thailand and to show that CTX-M ESBL is highly endemic in the country.

The emergence of a novel ceftazidime-resistant CTX-M extended-spectrum beta-lactamase, CTX-M-55, in both community-onset and hospital-acquired infections in Thailand

We report a novel CTX-M type of extended-spectrum beta-lactamase (ESBL), designated CTX-M-55, among 7 patients who had infection with ESBL-producing Escherichia coli or Klebsiella pneumoniae at a university hospital in Thailand. The CTX-M-55 ESBL showed reduced susceptibility to ceftazidime. This investigation provides the relevant clinical and molecular epidemiology for the gene encoding for CTX-M-55 in the isolates from these patients.

Association of QnrB determinants and production of extended-spectrum beta-lactamases or plasmid-mediated AmpC beta-lactamases in clinical isolates of Klebsiella pneumoniae

Clinical isolates of Escherichia coli and Klebsiella pneumoniae producing extended-spectrum beta-lactamases or plasmid-mediated AmpC beta-lactamases were screened for qnrA and qnrB genes. QnrB was present in 54 of 54 DHA-1-producing K. pneumoniae isolates and 10 of 45 SHV-12-producing ones, suggesting that the distribution of plasmids conferring resistance to extended-spectrum cephalosporins and quinolones in clinical isolates of K. pneumoniae is widespread.

New β-lactamases: a paradigm for the rapid response of bacterial evolution in the clinical setting

Production of β-lactamases is one of the most common mechanisms of bacterial resistance to β-lactam antibiotics. In the clinical setting, the introduction of new classes of β-lactams has invariably been followed by the emergence of new β-lactamases capable of degrading them, as a paradigmatic example of rapid bacterial evolution under a rapidly changing selective environment. The scope of this article is to provide an overview on the recent evolution of β-lactamase-mediated resistance among bacterial pathogens. Focus is on the mechanisms of evolution and dissemination of enzymes of greater clinical impact, including the extended-spectrum β-lactamases, the AmpC-type β-lactamases and the carbapenemases, which are currently responsible for emerging resistance to the most recent and powerful β-lactams (the expanded-spectrum cephalosporins and the carbapenems) among major Gram-negative pathogens such as Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter.

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.

A nosocomial outbreak of Escherichia coli producing CTX-M-15 and OXA-30 beta-lactamase

During a survey of the prevalent subtypes of extended-spectrum beta -lactamases in a university hospital in Korea, a nosocomial outbreak of Escherichia coli producing CTX-M-15 and OXA-30 beta -lactamases was detected. The outbreak comprised various infections, including bloodstream infections and colonization, and persisted for several months in various areas of the hospital.

Dissemination of Proteus mirabilis isolates harboring CTX-M-14 and CTX-M-3 β-lactamases at 2 hospitals in Taiwan

From February to June 2003, 111 clinical isolates of Proteus mirabilis were mainly isolated from patients with respiratory or urinary tract infections hospitalized at 3 district hospitals (A, B, C) in central Taiwan. Among them, 34 (30.6%) strains, isolated within 2 hospitals (A and B), exhibited nonsusceptibility to cefotaxime with significant reduction of MIC (> or = 3 log2 dilution) by the effect of clavulanic acid, which confirmed the phenotype of extended-spectrum beta-lactamases (ESBLs). These ESBL producers were coresistant to gentamicin, isepamicin, and amikacin, but remained susceptible to ceftazidime (MIC, < or = 0.5 microg/mL) and meropenem (MIC, <0.5 microg/mL). By isoelectric focusing analysis, polymerase chain reaction, and nucleotide sequencing, we detected the presence of CTX-M-14 in 33 strains and CTX-M-3 in 6 strains (5 strains harboring both CTX-M-14 and CTX-M-3 enzymes). These beta-lactamase genes can be successfully transferred by the conjugative plasmid. Molecular epidemiology of the 34 ESBL-producing P. mirabilis strains by pulsed-field gel electrophoresis using SfiI restriction enzyme revealed 9 different genotypes, suggesting epidemic clones with intra- and interhospital spread. In conclusion, the broadly extended clonal spreading of CTX-M-type P. mirabilis was first discovered at the district hospitals in Taiwan.

Identification of a novel cephalosporinase (DHA-3) in Klebsiella pneumoniae isolated in Taiwan

A strain of Klebsiella pneumoniae resistant to cefoxitin and oxyimino-cephalosporins, but susceptible to cefepime, was isolated from an adult patient hospitalised in Taichung, Taiwan. Isoelectric focusing revealed three beta-lactamases with isoelectric points of 5.4, 8.2 and 7.9, respectively. Following PCR with plasmid DNA templates and gene sequencing, these enzymes were shown to correspond to TEM-1, SHV-5 and a novel DHA-1-like enzyme (designated DHA-3). The bla genes for TEM-1 and SHV-5 were transferable, but the bla(DHA-3) gene was non-self-transferable in conjugation experiments. All three bla genes were successfully introduced by electrotransformation into an Escherichia coli recipient (DH5alpha), resulting in a similar resistance profile to that observed in the original donor strain. Other K. pneumoniae strains producing DHA-1-like enzymes have been identified previously in Taiwan, and this report suggests that DHA-type beta-lactamases are continuing to emerge in this country.

Multidrug resistance in Gram-negative bacteria that produce extended-spectrum beta-lactamases (ESBLs)

In 1983, just two years after the introduction of the oxymino-beta-lactams to the market , the first extended-spectrum beta-lactamases were isolated in Germany from Klebsiella pneumoniae strains. Since then several outbreaks have been reported in many European countries and the USA, and nowadays in several places worldwide the problem seems to reach endemic dimensions, with rates exceeding 50% in some countries, such as Portugal and Turkey. On the other hand not only K. pneumoniae but also Escherichia coli strains, with Enterobacter aerogenes predominating among the other enterobacteriaceal species, are increasingly reported as ESBL producers. In this review types, molecular characteristics, detection methods, epidemiology as well as interventions for therapy and antibiotic strategies to prevent and control infections caused by ESBL-producing microorganisms, are presented and discussed.

Dissemination of SHV-12 and CTX-M-type extended-spectrum beta-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae and emergence of GES-3 in Korea

OBJECTIVES

To assess the prevalence and genotypes of Ambler class A extended-spectrum beta-lactamases (ESBLs) in Korea.

METHODS

Clinical isolates of Escherichia coli and Klebsiella pneumoniae collected from 12 Korean hospitals during February-July 2003 were evaluated. Antimicrobial susceptibilities were determined by disc diffusion and agar dilution methods, and the putative ESBL-producing strains were tested by the double-disc synergy method. Detection of genes encoding class A beta-lactamases was performed by PCR amplification, and the PCR products were subjected to direct sequencing.

RESULTS

The double-disc synergy test showed positive results in 9.3% (23/246) of E. coli and 23.0% (55/239) of K. pneumoniae isolates. The most prevalent types of Ambler class A ESBLs in E. coli isolates were CTX-M-15 (n = 4) and CTX-M-3 (n = 3), and those in K. pneumoniae isolates were SHV-12 (n = 30) and CTX-M-3 (n = 13). Two isolates produced both SHV-12 and GES-3, simultaneously.

CONCLUSIONS

CTX-M-type and/or SHV-12 ESBL-producing E. coli and K. pneumoniae isolates are spreading, and a GES-type ESBL has emerged in Korea.

Molecular typing of Klebsiella pneumoniae isolates from public hospitals in Recife, Brazil

Thirty nosocomial isolates of Klebsiella pneumoniae, collected from three public hospitals in Recife, Brazil, between 1999 and 2000, were analysed in order to determine their epidemiological relatedness and genetic characteristics. The isolates were characterised by biotyping, antibiotyping, protein analysis, plasmid profile and random amplified polymorphic DNA (RAPD). The majority of the clinical isolates were resistant to multiple antibiotics, in particular to beta-lactams, and 30% were found to be ESBLs producers. RAPD proved to be the most effective technique in discriminating unrelated K. pneumoniae isolates. It was confirmed by the highly genetic similarity found among related isolates from an hospital outbreak. We conclude that K. pneumoniae infections in Recife has been caused by a variety of bacterial genotypes. This is the first report that revealed the subtypes of K. pneumoniae in Brazil by plasmid analysis and RAPD.

Occurrence of CTX-M-3, CTX-M-15, CTX-M-14, and CTX-M-9 extended-spectrum beta-lactamases in Enterobacteriaceae clinical isolates in Korea

Among 603 isolates of Enterobacteriaceae collected between June and November 2003 from three university hospitals within Korea, bla(CTX-M-3), bla(CTX-M-15), bla(CTX-M-14), and bla(CTX-M-9) were detected in 41 isolates of species from five different genera of Enterobacteriaceae, Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii, Enterobacter spp., and Serratia marcescens.

Molecular diversity of Proteus mirabilis isolates producing extended-spectrum β-lactamases in a French university hospital

Between February 1997 and December 2002, 3340 hospitalised patients yielded samples positive for Proteus mirabilis, of whom 45 (1.3%) were colonised/infected by P. mirabilis producing extended-spectrum beta-lactamases (ESBLs). The gross incidence of patients colonised/infected by ESBL-producing P. mirabilis was 1.61/10(5) days of hospitalisation, with 20% of isolates being collected from patients in urology wards, most frequently (53.3%) from urine samples. Seventeen (37.7%) of the 43 isolates were obtained from samples collected within 48 h of hospitalisation, indicating that they were community-acquired. Isoelectric focusing assays and sequencing identified the TEM-24, TEM-92 and TEM-52 ESBLs. Pulsed-field gel electrophoresis revealed eight pulsotypes (I-VIII), with the two most common pulsotypes, IV and VI, comprising ten (23.3%) and 12 (26.6%) isolates, respectively. These pulsotypes were considered to represent epidemic strains and spread in various wards of the hospital.

CTX-M and SHV-12 β-lactamases are the most common extended-spectrum enzymes in clinical isolates ofEscherichia coliandKlebsiella pneumoniaecollected from 3 university hospitals within Korea

Among the 443 clinical isolates of Escherichia coli and Klebsiella spp. collected between June and November 2003 from 3 university hospitals in Korea, 62 isolates were confirmed as extended-spectrum beta-lactamase (ESBL)- or plasmid-mediated AmpC beta-lactamase-producers by double disk synergy test, PCR and sequencing for beta-lactamase genes. The most frequently identified ESBL gene among E. coli and K. pneumoniae isolates was bla(SHV-12) and bla(CTX-M) (bla(CTX-M-9), bla(CTX-M-14), bla(CTX-M-3), and bla(CTX-M-15)). Four kinds of plasmid-mediated AmpC beta-lactamases, ACT-1, CMY-1, CMY-2, and DHA-1, were detected. ESBL production was associated with high levels of resistance to tetracycline, sulfisoxazole, streptomycin, kanamycin, gentamicin and tobramycin when compared to non-ESBL producing isolates. Conclusively, this study suggests that the CTX-M beta-lactamases are prevalent and various kinds of plasmid-mediated AmpC enzymes are distributed in clinical isolates of E. coli and Klebsiella spp. in Korea.

Occurrence of extended-spectrum beta-lactamases in members of the genus Shigella in the Republic of Korea

A nationwide survey was carried out in Korea to assess the prevalence of Shigella strains producing extended-spectrum beta-lactamases (ESBLs). From 1991 to 2002, 5,911 clinical strains were isolated and screened for resistance to extended-spectrum cephalosporins. Twenty of the Shigella isolates were ESBL positive, based on the synergistic effects between clavulanate and selected beta-lactams (ceftazidime and cefotaxime). Nucleotide sequence analysis of these isolates revealed that they harbored bla(TEM-19) (eight isolates), bla(TEM-15) (five isolates), bla(TEM-52) (six isolates), bla(TEM-17) (one isolate), bla(TEM-20) (one isolate), and bla(CTX-M-14) (three isolates). All the ESBL-encoding genes in this study were carried in conjugable plasmids. Thus, TEM-19, TEM-15, TEM-52, and CTX-M-14 beta-lactamases can be considered common Korean ESBL types in Shigella sonnei and are probably transmitted through interspecies spread between medical facilities and the community in Korea. This is the first report of the presence of TEM-17, TEM-19, and TEM-20 in Korea and in S. sonnei.

Epidemiology and clinical features of bloodstream infections caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae

Cases of bacteremia caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae isolates were retrospectively studied to determine the epidemiologic features and clinical outcomes of bloodstream infections. Among 389 blood isolates recovered from 1998 to 2002, 65 isolates (16.7%) were found to be extended-spectrum beta-lactamase (ESBL) or AmpC beta-lactamase producers. The beta-lactamases from 61 of the 65 isolates were characterized; 28 of 61 isolates produced AmpC-type enzymes (14 isolates each produced DHA-1 and CMY-1-like enzymes), 32 isolates produced TEM or SHV-related ESBLs, and 1 isolate produced a CTX-M-14-like enzyme. To compare the clinical features and outcomes of bloodstream infections caused by AmpC producers with those caused by TEM- or SHV-related ESBL producers, 27 patients infected with isolates producing AmpC-type enzymes (AmpC group) and 25 patients infected with isolates producing TEM- or SHV-related enzymes (ESBL group) were analyzed. There was no significant difference between the AmpC and the ESBL groups in terms of risk factors. When the initial response was assessed at 72 h after antimicrobial therapy, the treatment failure rate for the AmpC group was 51.9% (14 of 27 patients) and the 7- and 30-day mortality rates were 14.8 and 29.6%, respectively, which were similar to those for the ESBL group. When the mortality rate for the patients who received extended-spectrum cephalosporins as definitive treatment was assessed, all four patients in the DHA-1 group and one of three patients in the CMY-1-like group died. In summary, the prevalence of AmpC enzyme-producing K. pneumoniae was high at the Seoul National University Hospital, and the clinical features and outcomes for the patients infected with AmpC-producing organisms were similar to those for the patients infected with TEM- or SHV-related ESBL producers.

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.

High prevalence of extended-spectrum beta-lactamase-producing strains among blood isolates of Enterobacter spp. collected in a tertiary hospital during an 8-year period and their antimicrobial susceptibility patterns

Of 72 blood isolates of Enterobacter spp. collected over an 8-year period, 50% (36 of 72) were derepressed or partially derepressed AmpC mutants. The extended-spectrum beta-lactamase (ESBL) production rate was 43% (31 of 72 isolates), and 67.3% (31 of 46) of extended-spectrum cephalosporin-resistant strains produced ESBLs. Thus, a confirmatory test for ESBL production is necessary for extended-spectrum cephalosporin-resistant Enterobacter spp.

Detection of extended-spectrum beta-lactamase-producing, multidrug-resistant environmental isolates of Escherichia coli that bind to human bladder cells

Compared to the number of studies examining extended-spectrum beta-lactamase (ESBL)-producing clinical isolates, environmental ESBL-producers have not been studied extensively. To investigate environmental ESBL-producing Escherichia coli, 22 cephalothin-resistant E. coli were isolated from Han River in Seoul, Korea. These isolates were resistant to ampicillin, cephalothin, and gentamicin, and 14 isolates among these were resistant to norfloxacin. All of these isolates produce AmpC and CMY, OXA, or TEM as determined by isoelectric point focusing (IEF) gel electrophoresis and PCR. One isolate (57-214) producing AmpC and OXA was resistant to all antibiotics (ampicillin, cephalothin, norfloxacin, gentamicin, cefotaxime, ceftazidime) tested in this study. Six isolates, including isolate 57-214, could adhere to T24 human bladder cells, and these isolates were not related to each other as shown with random amplified polymorphic DNA (RAPD). Results showed that environmental ESBL-producing E. coli is able to colonize in bladder cells and directly cause antibiotic-resistant urinary tract infection.