Prevalence of SHV-12 among clinical isolates of Klebsiella pneumoniae producing extended-spectrum beta-lactamases and identification of a novel AmpC enzyme (CMY-8) in Southern Taiwan

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.

Epidemiology of extended-spectrum β-lactamases in Enterobacterales in Taiwan for over two decades

The emergence of antimicrobial resistance among microorganisms is a serious public health concern, and extended-spectrum β-lactamases (ESBL)-producing Enterobacterales is one of the major concerns among antibiotic-resistant bacteria. Although the prevalence of ESBL in Enterobacterales has been increasing with time, the prevalence of ESBL could differ according to the species, hospital allocation, sources of infections, nosocomial or community acquisitions, and geographic regions. Therefore, we conducted a comprehensive review of the epidemiology of ESBL-producing Enterobacterales in Taiwan. Overall, the rates of ESBL producers are higher in northern regions than in other parts of Taiwan. In addition, the genotypes of ESBL vary according to different Enterobacterales. SHV-type ESBLs (SHV-5 and SHV-12) were the major types of Enterobacter cloacae complex, but Serratia marcescens, Proteus mirabilis, Escherichia coli, and Klebsiella pneumoniae were more likely to possess CTX-M-type ESBLs (CTX-M-3 and CTX-M-14). Moreover, a clonal sequence type of O25b-ST131 has been emerging among urinary or bloodstream E. coli isolates in the community in Taiwan, and this clone was potentially associated with virulence, ESBL (CTX-M-15) production, ciprofloxacin resistance, and mortality. Finally, the evolution of the genetic traits of the ESBL-producing Enterobacterales isolates helps us confirm the interhospital and intrahospital clonal dissemination in several regions of Taiwan. In conclusion, continuous surveillance in the investigation of ESBL production among Enterobacterales is needed to establish its long-term epidemiology.

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.

Prevalence of Multidrug-Resistant CTX-M Extended Spectrum Beta-Lactamase-Producing Escherichia coli From Different Bovine Faeces in China

CTX-M extended spectrum beta-lactamase-producing Escherichia coli cause severe health hazards in livestock breeding. To date, little is known about antibiotic resistance differences among bacterial isolates from yaks, cows, and beef cattle; therefore, the aims of this study were to analyse the prevalence of CTX-M-producing E. coli in yak, beef cattle, and dairy cattle feces from different provinces in China. A total of 790 fecal samples from yaks, beef cattle, and dairy cows were used. Among all the samples, 523 non duplicate E. coli isolates were identified, and 29.6% of samples harbored CTX-M producers. The results showed that these E. coli strains harbored 15 clusters of CTX-M genes: CTX-M-79, CTX-M-55, CTX-M-15, CTX-M-14, CTX-M-28, CTX-M-179, CTX-M-65, CTX-M-24, CTX-M-27, CTX-M-102, CTX-M-105, CTX-M-173, CTX-M-238, CTX-M-196, and CTX-M-10. The dominant resistance genes were CTX-M-15, CTX-M-14, and CTX-M-55. Moreover, the distribution of CTX-M genes was related to geographical region. Based on the above findings, we reasoned that bovines are potential reservoirs of antibiotic resistance, and this problem should be given adequate attention.

Extended-spectrum β-lactamases: an update on their characteristics, epidemiology and detection

Extended-spectrum β-lactamase (ESBL)-producing Gram-negative pathogens are a major cause of resistance to expanded-spectrum β-lactam antibiotics. Since their discovery in the early 1980s, they have spread worldwide and an are now endemic in Enterobacterales isolated from both hospital-associated and community-acquired infections. As a result, they are a global public health concern. In the past, TEM- and SHV-type ESBLs were the predominant families of ESBLs. Today CTX-M-type enzymes are the most commonly found ESBL type with the CTX-M-15 variant dominating worldwide, followed in prevalence by CTX-M-14, and CTX-M-27 is emerging in certain parts of the world. The genes encoding ESBLs are often found on plasmids and harboured within transposons or insertion sequences, which has enabled their spread. In addition, the population of ESBL-producing Escherichia coli is dominated globally by a highly virulent and successful clone belonging to ST131. Today, there are many diagnostic tools available to the clinical microbiology laboratory and include both phenotypic and genotypic tests to detect β-lactamases. Unfortunately, when ESBLs are not identified in a timely manner, appropriate antimicrobial therapy is frequently delayed, resulting in poor clinical outcomes. Several analyses of clinical trials have shown mixed results with regards to whether a carbapenem must be used to treat serious infections caused by ESBLs or whether some of the older β-lactam-β-lactamase combinations such as piperacillin/tazobactam are appropriate. Some of the newer combinations such as ceftazidime/avibactam have demonstrated efficacy in patients. ESBL-producing Gram-negative pathogens will continue to be major contributor to antimicrobial resistance worldwide. It is essential that we remain vigilant about identifying them both in patient isolates and through surveillance studies.

Characterization of blaNDM-1- and blaSHV-12-Positive IncX3 Plasmid in an Enterobacter Hormaechei New Sequence Type 1000 from China

Purpose

Carbapenem-resistant Enterobacter cloacae complex has been reported worldwide and becomes a new challenge for clinical management. The present study was to characterize the IncX3 plasmid encoding bla_NDM-1 and bla_SHV-12 gene in E. hormaechei sequence.

Materials and Methods

EcHK001 was recovered from the sputum sample of a patient. Species identification and antimicrobial susceptibility testing were performed using the VITEK 2 system, while further classification was carried out by hsp60 typing. The presence of NDM-1 was detected by PCR and sequencing. Conjugation experiments and southern blotting were carried out to determine the transferability of the NDM-1-carrying plasmid. Whole-genome sequencing and analysis were conducted to better understand the molecular characteristics of the multi-drug resistant isolate.

Results

Strain EcHK001 was classified as E. hormaechei of new sequence type 1000. Multiple drug-resistant genes were detected. The bla_NDM-1 and bla_SHV-12 genes were located on a self-transferable IncX3 plasmid. Synonymous mutations were identified in the genes encoding TEM-1 and ACT-17. Phylogenetic analysis indicated that EcHK001 clustered into a different clade from domestic strains.

Conclusion

The rapid spread of the recurrent IncX3 plasmid highlights the need for continuous surveillance of the NDM-1 dissemination. The presence of mutations in existing carbapenem-resistant genes may generate potential new variants and raise serious challenges for clinical treatment.

blaVIM- and blaOXA-mediated carbapenem resistance among Acinetobacter baumannii and Pseudomonas aeruginosa isolates from the Mulago hospital intensive care unit in Kampala, Uganda

Background

Between January 2015 and July 2017, we investigated the frequency of carbapenem resistant Acinetobacter baumannii (CRAB) and carbapenem resistant Pseudomonas aeruginosa (CRPA) at the Mulago Hospital intensive care unit (ICU) in Kampala, Uganda. Carbapenemase production and carbapenemase gene carriage among CRAB and CRPA were determined; mobility potential of carbapenemase genes via horizontal gene transfer processes was also studied.

Methods

Clinical specimens from 9269 patients were processed for isolation of CRAB and CRPA. Drug susceptibility testing was performed with the disk diffusion method. Carriage of carbapenemase genes and class 1 integrons was determined by PCR. Conjugation experiments that involved bla_VIM positive CRAB/CRPA (donors) and sodium azide resistant Escherichia coli J53 (recipient) were performed.

Results

The 9269 specimens processed yielded 1077 and 488 isolates of Acinetobacter baumannii and Pseudomonas aeruginosa, respectively. Of these, 2.7% (29/1077) and 7.4% (36/488) were confirmed to be CRAB and CRPA respectively, but 46 were available for analysis (21 CRAB and 25 CRPA). Majority of specimens yielding CRAB and CRPA were from the ICU (78%) while 20 and 2% were from the ENT (Ear Nose & Throat) Department and the Burns Unit, respectively. Carbapenemase assays performed with the MHT assay showed that 40 and 33% of CRPA and CRAB isolates respectively, were carbapenemase producers. Also, 72 and 48% of CRPA and CRAB isolates respectively, were metallo-beta-lactamase producers. All the carbapenemase producing isolates were multidrug resistant but susceptible to colistin. bla_VIM was the most prevalent carbapenemase gene, and it was detected in all CRAB and CRPA isolates while bla_OXA-23 and bla_OXA-24 were detected in 29 and 24% of CRAB isolates, respectively. Co-carriage of bla_OXA-23 and bla_OXA-24 occurred in 14% of CRAB isolates. Moreover, 63% of the study isolates carried class 1 integrons; of these 31% successfully transferred bla_VIM to E. coli J53.

Conclusions

CRAB and CRPA prevalence at the Mulago Hospital ICU is relatively low but carbapenemase genes especially bla_VIM and bla_OXA-23 are prevalent among them. This requires strengthening of infection control practices to curb selection and transmission of these strains in the hospital.

The Molecular and Clinical Epidemiology of Extended-Spectrum Cephalosporin- and Carbapenem-Resistant Enterobacteriaceae at 4 US Pediatric Hospitals

OBJECTIVE

In this report, we aim to describe the epidemiology of extended-spectrum cephalosporin-resistant (ESC-R) and carbapenem-resistant (CR) Enterobacteriaceae infections in children.

METHODS

ESC-R and CR Enterobacteriaceae isolates from normally sterile sites of patients aged <22 years from 4 freestanding pediatric medical centers were collected along with the associated clinical data.

RESULTS

The overall frequencies of ESC-R and CR isolates according to hospital over the 4-year study period ranged from 0.7% to 2.8%. Rates of ESC-R or CR Escherichia coli and Klebsiella pneumoniae varied according to hospital and ranged from 0.75 to 3.41 resistant isolates per 100 isolates (P < .001 for any differences). E coli accounted for 272 (77%) of the resistant isolates; however, a higher rate of resistance was observed in K pneumoniae isolates (1.78 vs 1.27 resistant isolates per 100 same-species isolates, respectively; P = .005). One-third of the infections caused by ESC-R or CR E coli were community-associated. In contrast, infections caused by ESC-R or CR K pneumoniae were more likely than those caused by resistant E coli to be healthcare- or hospital-associated and to occur in patients with an indwelling device (P ≤ .003 for any differences, multivariable logistic regression). Nonsusceptibility to 3 common non-β-lactam agents (ciprofloxacin, gentamicin, and trimethoprim-sulfamethoxazole) occurred in 23% of the ESC-R isolates. The sequence type 131-associated fumC/fimH-type 40-30 was the most prevalent sequence type among all resistant E coli isolates (30%), and the clonal group 258-associated allele tonB79 was the most prevalent allele among all resistant K pneumoniae isolates (10%).

CONCLUSIONS

The epidemiology of ESC-R and CR Enterobacteriaceae varied according to hospital and species (E coli vs K pneumoniae). Both community and hospital settings should be considered in future research addressing pediatric ESC-R Enterobacteriaceae infection.

Antibiotic Prophylaxis Is Associated with Subsequent Resistant Infections in Children with an Initial Extended-Spectrum-Cephalosporin-Resistant Enterobacteriaceae Infection

The objective of this study was to assess the association between previous antibiotic use, particularly long-term prophylaxis, and the occurrence of subsequent resistant infections in children with index infections due to extended-spectrum-cephalosporin-resistant Enterobacteriaceae We also investigated the concordance of the index and subsequent isolates. Extended-spectrum-cephalosporin-resistant Escherichia coli and Klebsiella spp. isolated from normally sterile sites of patients aged <22 years were collected along with associated clinical data from four freestanding pediatric centers. Subsequent isolates were categorized as concordant if the species, resistance determinants, and fumC-fimH (E. coli) or tonB (Klebsiella pneumoniae) type were identical to those of the index isolate. In total, 323 patients had 396 resistant isolates; 45 (14%) patients had ≥1 subsequent resistant infection, totaling 73 subsequent resistant isolates. The median time between the index and first subsequent infections was 123 (interquartile range, 43 to 225) days. In multivariable Cox proportional hazards analyses, patients were 2.07 times as likely to have a subsequent resistant infection (95% confidence interval, 1.11 to 3.87) if they received prophylaxis in the 30 days prior to the index infection. In 26 (58%) patients, all subsequent isolates were concordant with their index isolate, and 7 (16%) additional patients had at least 1 concordant subsequent isolate. In 12 of 17 (71%) patients with E. coli sequence type 131 (ST131)-associated type 40-30, all subsequent isolates were concordant. Subsequent extended-spectrum-cephalosporin-resistant infections are relatively frequent and are most commonly due to bacterial strains concordant with the index isolate. Further study is needed to assess the role prophylaxis plays in these resistant infections.

Colistin-resistant Escherichia coli clinical isolate harbouring the mcr-1 gene in Ecuador

Colistin resistance mediated by the mcr-1 gene has been reported worldwide, but to date not from the Andean region, South America. We report the first clinical isolate of Escherichia coli harbouring the mcr-1 gene in Ecuador. The strain was isolated from peritoneal fluid from a 14-year-old male with acute appendicitis, and subjected to molecular analysis. The minimum inhibitory concentration of colistin for the strain was 8 mg/ml and it was susceptible to carbapenems but resistant to tigecycline. The strain harboured mcr-1 and blaCTX-M-55 genes and was of sequence type 609. The recognition of an apparently commensal strain of E. coli harbouring mcr-1 serves as an alert to the presence in the region of this recently described resistance mechanism to one of the last line of drugs available for the treatment of multi-resistant Gram-negative infections.

Previous Antibiotic Exposure Increases Risk of Infection with Extended-Spectrum-β-Lactamase- and AmpC-Producing Escherichia coli and Klebsiella pneumoniae in Pediatric Patients

The objective of this study was to determine whether antibiotic exposure is associated with extended-spectrum-beta-lactamase- or AmpC-producing Escherichia coli or Klebsiella pneumoniae infections in children. We collected extended-spectrum-beta-lactamase- or AmpC-producing E. coli or K. pneumoniae isolates and same-species susceptible controls from normally sterile sites of patients aged ≤21 years, along with associated clinical data, at four free-standing pediatric centers. After controlling for potential confounders, the relative risk of having an extended-spectrum-beta-lactamase-producing isolate rather than a susceptible isolate was 2.2 times higher (95% confidence interval [CI], 1.49 to 3.35) among those with antibiotic exposure in the 30 days prior to infection than in those with no antibiotic exposure. The results were similar when analyses were limited to exposure to third-generation cephalosporins, other broad-spectrum beta-lactams, or trimethoprim-sulfamethoxazole. Conversely, the relative risk of having an AmpC-producing versus a susceptible isolate was not significantly elevated with any antibiotic exposure in the 30 days prior to infection (adjusted relative risk ratio, 1.12; 95% CI, 0.65 to 1.91). However, when examining subgroups of antibiotics, the relative risk of having an AmpC-producing isolate was higher for patients with exposure to third-generation cephalosporins (adjusted relative risk ratio, 4.48; 95% CI, 1.75 to 11.43). Dose-response relationships between antibiotic exposure and extended-spectrum-beta-lactamase-producing or AmpC-producing isolates were not demonstrated. These results reinforce the need to study and implement pediatric antimicrobial stewardship strategies, and they indicate that epidemiological studies of third-generation cephalosporin-resistant E. coli and K. pneumoniae isolates should include resistance mechanisms when possible.

Molecular detection of antimicrobial resistance in local isolates of Staphylococcus epidermidis from urinary tract infections in Faisalabad region of Pakistan

Staphylococci are one of the foremost causes of urinary tract infections (UTIs) in humans. The emergence of multiple drug resistance (MDR) among Staphylococci poses serious challenges in antimicrobial therapy for UTIs. Most work has been done on S. aureus while coagulase negative Staphylococci (mainly S. epidermidis) are often neglected. This study was conducted to establish a baseline profile of drug resistance in local S. epidermidis isolates from UTIs. Eighty urine samples were collected from suspected UTIs cases and screened for S. epidermidis. Twenty isolates were suspected as S. epidermidis based on colony morphology and Gram staining. Molecular detection by polymerase chain reaction (PCR) confirmed 13 isolates as S. epidermidis. Using disc diffusion method, phenotypic drug resistance of the isolates was observed towards erythromycin (100 %), gentamycin, azithromycin and tetracycline (92.3 %), ampicillin and oxytetracyclin (84.6 %), amikacin and srteptomycin (76.9 %), methicillin (69.2 %), cephradine, cefaclor and cefazolin (53.8 %) and vancomycin (15.3 %). Eighteen most commonly reported genes responsible for conferring resistance towards these drugs were targeted by PCR: among these tetM gene was found most prevalent (46.1 %) followed by tetK (30.7 %), aac(6')/aph(2") (30.7 %), aacA-aphD (23 %), ermA (23 %), blaZ (23 %), mecA (23 %) blaTEM-1 (23 %), MeccA (23 %) and mecA (15.3 %). No gene fragment for vancomycin resistance was detected. The salient finding was that all S. epidermidis isolates were multiple drugs resistant as they showed resistance against at least three structurally different antimicrobial agents. It is concluded that in addition to the mostly used antimicrobial agent vancomycin, the cephalosporins including cephradine, cefaclor and cefazolin are also the drugs of choice against UTIs caused by S. epidermidis.

Surveillance in Taiwan Using Molecular Epidemiology for Extended-Spectrum Beta-Lactamase-ProducingKlebsiella pneumoniae

Objective:

To evaluate intrahospital and interhospital clonal dissemination of extended-spectrum beta-lactamase (ESBL)-producing strains ofKlebsiella pneumoniae.

Setting:

Eight tertiary-care university hospitals and 16 regional hospitals in Taiwan.

Methods:

Two hundred eleven confirmed ESBL-producing isolates ofK. pneumoniaewere collected from January 1998 to June 2000. The isolates were characterized by various typing methods, including antibiogram (9 antimicrobial agents), computer-based ribotyping, pulsed-field gel electrophoresis (PFGE), and isoelectric focusing of beta-lactamase.

Results:

Ribotyping identified 70 distinct ribogroups among 200 isolates evaluated. Forty-three of these ribogroups were unique. Eleven ribogroups, comprising 115 isolates, were detected in more than one hospital (interhospital dissemination), whereas 16 groups (42 isolates) were detected in more than one patient within a hospital (intrahospital dissemination). The combination of ribotyping and PFGE identified two large epidemic clones, which were called 691.5/PFGE-G and 595.7/PFGE-A. These epidemic clones were detected mainly in the hospitals located in the northern and central regions of Taiwan. However, variation of the profiles of antibiograms and isoelectric focusing was apparent within each clone. In addition, isolates with the same isoelectric focusing profile (isoelectric points 7.9, 8.2, and 8.4) and antibiogram (resistance to 9 compounds evaluated) were present among different molecular-typed clones.

Conclusions:

Our results showed that clonal dissemination (both interhospital and intrahospital dissemination) is occurring in several regions of Taiwan. Rapid computer-based ribotyping associated with PFGE demonstrated multiple epidemic clones of ESBL-producingK. pneumoniaein Taiwan. The combination of phenotypic and molecular methods has proved useful to characterize these epidemic clones.

Pediatric carbapenem-resistant Enterobacteriaceae in Los Angeles, California, a high-prevalence region in the United States

BACKGROUND

Infections caused by carbapenem-resistant Enterobacteriaceae (CRE) are on the rise worldwide but are not well described in pediatric populations. This study characterizes the clinical, phenotypic and genotypic characteristics of CRE infections at a free-standing US children's hospital.

METHODS

CRE were defined as any clinical Enterobacteriaceae isolate non-susceptible to either imipenem or meropenem and resistant to ceftriaxone, cefotaxime and ceftazidime determined by routine antimicrobial susceptibility testing. The modified Hodge test was performed to screen for the production of carbapenemase. Clinical data were reviewed, and molecular characterization of phylogenetic and resistance-associated traits was performed.

RESULTS

CRE isolates were recovered from sterile and non-sterile sites in 10 patients, 6 weeks to 24 years of age, between 2011 and 2013. Co-morbidities included hematologic, genetic and urologic abnormalities. Two patients had traveled abroad (India, Lebanon) before CRE recovery. Carbapenemase determinants were detected in 5 cases, including KPC-3 in 2 Klebsiella pneumoniae (ST258 and ST18) and 1 Escherichia coli (ST131), and NDM-1 in 1 K. pneumoniae (ST37) and 1 E. coli (ST101) isolate. Additional resistance determinants were detected, including CTX-M-15, SHV-11, TEM-1, CMY-2, CMY-4 and CMY-42. Four patients died, including 2 of 3 patients with CRE bacteremia. There was no evidence of epidemiologic or molecular relatedness between any 2 cases.

CONCLUSIONS

This report documents the appearance of highly resistant Gram-negative pathogens in a vulnerable patient population at a pediatric tertiary referral center in a major US metropolitan area. Detailed understanding of the distribution and spread of CRE is essential for the timely detection and containment of these perilous pathogens.

Pediatric infection and intestinal carriage due to extended-spectrum-cephalosporin-resistant Enterobacteriaceae

The objective of this study is to describe the epidemiology of intestinal carriage with extended-spectrum-cephalosporin-resistant Enterobacteriaceae in children with index infections with these organisms. Patients with resistant Escherichia coli or Klebsiella bacteria isolated from the urine or a normally sterile site between January 2006 and December 2010 were included in this study. Available infection and stool isolates underwent phenotypic and molecular characterization. Clinical data relevant to the infections were collected and analyzed. Overall, 105 patients were identified with 106 extended-spectrum-cephalosporin-resistant E. coli (n = 92) or Klebsiella (n = 14) strains isolated from urine or a sterile site. Among the 27 patients who also had stool screening for resistant Enterobacteriaceae, 17 (63%) had intestinal carriage lasting a median of 199 days (range, 62 to 1,576). There were no significant differences in demographic, clinical, and microbiological variables between those with and those without intestinal carriage. Eighteen (17%) patients had 37 subsequent resistant Enterobacteriaceae infections identified: 31 urine and 6 blood. In a multivariable analysis, antibiotic intake in the 91 days prior to subsequent urine culture was significantly associated with subsequent urinary tract infection with a resistant organism (hazard ratio, 14.3; 95% confidence interval [CI], 1.6 to 130.6). Intestinal carriage and reinfection were most commonly due to bacterial strains of the same sequence type and with the same resistance determinants as the index extended-spectrum-cephalosporin-resistant Enterobacteriaceae, but carriage and reinfection with different resistant Enterobacteriaceae strains also occurred.

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.

Prevalence and characteristics of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae isolated from pediatric inpatients with respiratory tract infections at a teaching hospital in China

The aim of this study was to investigate the prevalence and characteristics of resistant Klebsiella pneumoniae isolates in the pediatric setting in China. A total of 201 non-duplicate K. pneumoniae isolates were obtained from 432 pediatric inpatients suffering from respiratory tract infections. One hundred and thirty-eight K. pneumoniae isolates were determined to be extended-spectrum beta-lactamase-producers. Of all ESBL-producing isolates, 138 (100%) were resistant to piperacillin, ampicillin, cefazolin, and aztreonam, 136 (98.4%) to cefuroxime, 126 (91.2%) to ceftriaxone and co-trimoxazole, 120 (87.4%) to cefoperazone, 91 (65.8%) to ceftazidime, 78 (56.5%) to gentamicin, and 72 (52.4%) to cefepime. TEM was the main type of beta-lactamase among ESBL-producing K. pneumoniae, followed by SHV and CTX-M-1. Of the 30 isolates harboring CTX-M-producers, 53.3% co-produced TEM, 36.7% co-produced SHV, and the remaining isolates co-produced SHV and TEM. The data show that there is a high prevalence of ESBL-producing K. pneumoniae infections among pediatric inpatients in the region.

Emergence of extended-spectrum β-lactam resistance among Escherichia coli at a US academic children's hospital is clonal at the sequence type level for CTX-M-15, but not for CMY-2

Resistance to extended-spectrum β-lactams is increasing worldwide among Escherichia coli and has been linked to a small number of emergent clones (e.g. ST38, ST131 and ST405) recovered from extraintestinal infections in community and hospital settings. There are, however, limited data about the relative contributions of bacterial strains, plasmids and β-lactamase genes to extended-spectrum β-lactam resistance in paediatric infections. We performed an extensive molecular analysis of phylogenetic, virulence and antibiotic resistance-related properties of 49 previously reported serial E. coli isolates recovered during 1999-2007 at Seattle Children's Hospital (Seattle, WA). Class C enzyme CMY-2 and class A enzyme CTX-M-15 were the most prominent extended-spectrum β-lactam resistance enzymes in the collection, first appearing in this patient population in 2001 and 2003, respectively, and then steadily increasing in frequency over the remainder of the study period. Among 19 CMY-2-positive isolates, 16 distinct STs were detected (D = 98.25%, 95% CI 96-100.25%), indicating that CMY spread is non-clonal at the host strain level. In contrast, among ten CTX-M-15-positive isolates, three STs were detected (D = 37.78%, 95% CI 2.36-73.20%), of which eight represented the worldwide-disseminated ST131 lineage, consistent with clonal spread of CTX-M-15-associated resistance. fimHTR subtyping of ten ST131 isolates (including two CTX-M-negative isolates) revealed that, within ST131, carriage of allele fimHTR30 correlated with CTX-M-15 positivity, whilst carriage of non-fimHTR30 alleles correlated with carriage of non-CTX-M enzymes. Thus, spread of CMY-2 is non-clonal at the ST level, but clonal spread of CTX-M-15 may be associated with a specific fimHTR-defined sublineage of ST131.

Discrepancy between effects of carbapenems and flomoxef in treating nosocomial hemodialysis access-related bacteremia secondary to extended spectrum beta-lactamase producing Klebsiella pneumoniae in patients on maintenance hemodialysis

Background

Hemodialysis (HD) patients are susceptible to extended spectrum beta-lactamase (ESBL)-producing bacterial infections. Because the optimal treatment and clinical significance of ESBL-producing Klebsiella pneumoniae (ESBL-Kp) HD access-related bacteremia remain unclear, we conducted this retrospective study to determine the clinical outcomes of patients treated with either flomoxef or a carbapenem.

Methods

The eligibility criterion was fistula or graft- or catheter- related ESBL-Kp bacteremia in patients on maintenance HD. The clinical characteristics and antibiotic management were analyzed. Outcome was determined by mortality resulting from bacteremia during the 14‐day period after the first positive blood culture for flomoxef-susceptible ESBL-Kp.

Results

The 57 patients studied were predominantly elderly, malnourished, with a history of severe illnesses and broad-spectrum antibiotic use before the onset of bacteremia, and with severe septicemia as determined by the Pitt bacteremia score (PBS). The study population comprised 7 fistula, 8 graft, and 42 HD catheter-related bacteremia (CRB) cases, and the mortality rate was high (36/57, 63.2%) in these 57 patients. Of 42 patients with CRB, those in the deceased group (27/42, 64.3%) had significantly lower levels of serum albumin, longer prior hospital stay and duration of catheter-dependent HD, and higher PBS than patients in the survived group. Failure to receive effective antibiotics (flomoxef or a carbapenem) within 5 days after onset of bacteremia and treatment with flomoxef both significantly contributed to higher mortality. Multivariate analyses revealed that flomoxef use, PBS, and catheter-dependent HD >30 days were independently associated with increased mortality (OR, 3.52; 95% CI, 1.19–58.17, OR, 2.92; 95% CI, 1.36–6.26 and OR, 5.73; 95% CI, 1.21–63.2, respectively).

Conclusions

Considering the high mortality rate, ESBL-Kp should be recognized as a possible pathogen in patients on maintenance HD at high risk of acquiring HD access infections associated with ESBL-producing bacteria. Carbapenems rather than flomoxef should be the therapy of choice in these critically vulnerable patients.

First detection of TEM-116 extended-spectrum β-lactamase in a Providencia stuartii isolate from a Tunisian hospital

PURPOSE

To study the resistance to third-generation cephalosporins in Providencia stuartii strain isolated from hospitalized patient in Tunisia and to identify the responsible genes

MATERIALS AND METHODS

This strain was analysed by PCR and sequencing to identify the genes responsible for the β-lactamase resistance phenotypes. The transferability of the phenotypes was tested by conjugation to Escherichia coli J53. The isoelectric point was determinate by isoelectrofocalisation.

RESULTS

This resistance was carried by a 60 kb plasmid that encoded a β-lactamase with a pI of 5.4. This β-lactamase revealed identity with the blaTEM-1 gene encoding the TEM-1 β-lactamase, except for a replacement of the Val residue at position 84 by Ile, and the Ala residue at position 184 by Val. These two mutations were encountered in TEM-116 β-lactamase.

CONCLUSION

This study demonstrates the first description of TEM-116 in the P. stuartii species in the world and the first one in a Tunisian hospital.

Bacteremia due to extended-spectrum-β-lactamase-producing Aeromonas spp. at a medical center in Southern Taiwan

Although extended-spectrum-β-lactamase (ESBL)-producing aeromonads have been increasingly reported in recent years, most of them were isolates from case reports or environmental isolates. To investigate the prevalence of ESBL producers among Aeromonas blood isolates and the genes encoding ESBLs, consecutive nonduplicate Aeromonas blood isolates collected at a medical center in southern Taiwan from March 2004 to December 2008 were studied. The ESBL phenotypes were examined by clavulanate combination disk test and the cefepime-clavulanate ESBL Etest. The presence of ESBL-encoding genes, including bla(TEM), bla(PER), bla(CTX-M), and bla(SHV) genes, was evaluated by PCR and sequence analysis. The results showed that 4 (2.6%) of 156 Aeromonas blood isolates, 1 Aeromonas hydrophila isolate and 3 Aeromonas caviae isolates, expressed an ESBL-producing phenotype. The ESBL gene in two A. caviae isolates was bla(PER-3), which was located in both chromosomes and plasmids, as demonstrated by Southern hybridization. Of four patients with ESBL-producing Aeromonas bacteremia, two presented with catheter-related phlebitis and the other two with primary bacteremia. Three patients had been treated with initial noncarbapenem β-lactams for 5 to 10 days, and all survived. In conclusion, ESBL producers exist among Aeromonas blood isolates, and clinical suspicion of ESBL production should be raised in treating infections due to cefotaxime-resistant Aeromonas isolates.

Molecular docking analysis of new generation cephalosporins interactions with recently known SHV-variants

Extended-spectrum-β-lactamases (ESBLs), constitutes the growing class of betalactamses, these are enzymes produced by bacteria which impart resistance against advanced-generation-cephalosporins. SHV enzymes are among the most prevalent ESBLs. The mode of molecular interactions of recent SHV-variants to advanced generation cephalosporins has not been reported yet. This is the first time we are reporting the insilico study of these recent variants with new generation cephaosporins. Homology models for SHV-105, SHV-95, SHV-89, SHV-61 and SHV-48 were generated using MODELLER9v3. New generation Cephalosporins were selected to target the active site amino acid residues of these modeled SHV enzymes for predicting comparative efficacies of these inhibitors against the said enzymes on the basis of interaction energies of docking. The docked complexes were analyzed by using DISCOVERY STUDIO 2.5. In this study A237, S70, K234, R275, N132, R244 and S130 were found crucial to the correct positioning of drugs within the binding site of SHV enzymes in 11, 6, 6, 6, 5, 5 and 5 instances, respectively. On the basis of interaction energy and Ki calculations cefatoxime emerged as the most efficient among the other advanced cephalosporins against all the studied SHV variants, excluding SHV-48 where ceftazidime was found to be most effective drug. Furthermore, this study identified amino acid residues crucial to ‘SHV-Cephalosporins’ interactions and this information will be useful in designing effective and versatile drug candidates.

Novel genetic environment of the plasmid-mediated KPC-3 gene detected in Escherichia coli and Citrobacter freundii isolates from China

The imipenem and meropenem-resistant strains Citrobacter freundii HS70 and Escherichia coli HS510 were isolated from patients in Shanghai, China. By isoelectric focusing, PCR amplification and sequencing, these strains were each found to produce four β-lactamases: TEM-1, KPC-3, SHV-7 and CTX-M-14. A conjugation experiment and plasmid restriction digestion revealed that the bla_KPC-3 gene was located on the same plasmid in both isolates. Bidirectional primer walking sequencing showed that the nucleotide sequence surrounding the 3.8 kb bla_KPC-3 contained a 671-bp insertion similar to that previously characterized in China. The insertion was located between the promoter and the coding region of the bla_KPC-3 gene. Susceptibility testing performed on recombinant strains carrying the bla_KPC-3 gene with or without the insertion revealed that minimum inhibitory concentrations of imipenem, meropenem, cefepime, and cefotaxime for E. coli EMU-KPC3 (without insertion) were four times higher than that of E. coli EKPC3 (with insertion). The 671 bp insertion reduced bla_KPC-3 expression significantly. Taken together, these results suggest that KPC-3-producing C. freundii and E. coli have begun to emerge in our hospital.

Laboratory surveillance for prospective plasmid-mediated AmpC beta-lactamases in the Kinki region of Japan

Extended-spectrum beta-lactamases, plasmid-mediated AmpC beta-lactamases (PABLs), and plasmid-mediated metallo-beta-lactamases confer resistance to many beta-lactams. In Japan, although several reports exist on the prevalence of extended-spectrum beta-lactamases and metallo-beta-lactamases, the prevalence and characteristics of PABLs remain unknown. To investigate the production of PABLs, a total of 22,869 strains of 4 enterobacterial species, Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis, were collected during six 6-month periods from 17 clinical laboratories in the Kinki region of Japan. PABLs were detected in 29 (0.13%) of 22,869 isolates by the 3-dimensional test, PCR analysis, and DNA sequencing analysis. PABL-positive isolates were detected among isolates from 13 laboratories. Seventeen of 13,995 (0.12%) E. coli isolates, 8 of 5,970 (0.13%) K. pneumoniae isolates, 3 of 1,722 (0.17%) K. oxytoca isolates, and 1 of 1,182 (0.08%) P. mirabilis isolates were positive for PABLs. Of these 29 PABL-positive strains, 20 (69.0%), 6 (20.7%), 2 (6.9%), and 1 (3.4%) carried the genes for CMY-2, DHA-1, CMY-8, and MOX-1 PABLs, respectively. Pattern analysis of randomly amplified polymorphic DNA and pulsed-field gel electrophoretic analysis revealed that the prevalence of CMY-2-producing E. coli strains was not due to epidemic strains and that 3 DHA-1-producing K. pneumoniae strains were identical, suggesting their clonal relatedness. In conclusion, the DHA-1 PABLs were predominantly present in K. pneumoniae strains, but CMY-2 PABLs were predominantly present in E. coli strains. The present findings will provide significant information to assist in preventing the emergence and further spread of PABL-producing bacteria.

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.

Novel CTX-M {beta}-lactamase genotype distribution and spread into multiple species of Enterobacteriaceae in Changsha, Southern China

OBJECTIVES

The aim of this study was to undertake a survey of the occurrence of CTX-M and SHV extended-spectrum beta-lactamase (ESBL) genotypes in Enterobacteriaceae from Hunan Province, China.

METHODS

Clinical isolates (425) from three major hospitals in Changsha, Hunan Province, were collected between October 2004 and July 2005, and their antimicrobial susceptibilities of the genotype of bla(CTX-M) and bla(SHV) were determined. Random amplified polymorphic DNA was used to characterize the clonality of all of the isolates.

RESULTS

The overall rate of ESBL-positive isolates was 33.4% (142/425). The dominant ESBLs were CTX-M types, and were found in 109/142 (76.8%) isolates comprising seven different genera/species, namely Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Enterobacter aerogenes, Citrobacter freundii, Proteus vulgaris and Providencia stuartii. The most common bla(CTX-M) genotypes were bla(CTX-M-14) (47.7%), bla(CTX-M-3) (29.4%) and bla(CTX-M-15) (17.4%). A novel gene derived from bla(CTX-M-15), bla(CTX-M-82) (Ala-40-->Pro), was identified.

CONCLUSIONS

The dominant ESBL genotype in Hunan Province was bla(CTX-M). The high prevalence (17.4%) of bla(CTX-M-15) has not previously been reported from China. Our results identify that an epidemic of bla(CTX-M) in Changsha, Hunan Province, has evolved with the appearance and spread of bla(CTX-M-15) against the dominant genotypes bla(CTX-M-14) and bla(CTX-M-3.) The worldwide dominance of bla(CTX-M-15) could be poised to spread to China, displacing the current prevailing genotypes.

Characterization of a novel AmpC-type plasmid-mediated beta-lactamase from an Escherichia coli strain isolated in China

The aim of this work was to study the phenotypic and molecular characterization of a novel plasmid-mediated AmpC beta-lactamase from Escherichia coli E384. Conjugation experiments, isoelectric focusing, pulsed-field gel electrophoresis, plasmid profiling, and Southern blot as well as PCR, sequencing techniques, and susceptibility testing were carried out to investigate the underlying mechanism of resistance. The kinetic parameters were determined to characterize the novel enzyme. MIR-4 beta-lactamase, pI 8.2, is a novel variant with four substitutions of amino acids compared with the sequence of MIR-1. E. coli E384 displays resistance to eight beta-lactam antimicrobial agents and three fluoroquinolones. The minimal inhibitory concentrations of beta-lactam in combination with beta-lactamase inhibitors show no significant synergy. Kinetic parameters suggest that the novel enzyme effectively hydrolyzes broad-spectrum beta-lactams. The same hybridization signal was detectable only in the 54-kb plasmid band that hybridized with the bla (CTX-M)- and bla(ampC)-specific probes. This is the first description of a plasmid-mediated MIR-4 enzyme in China. This study illustrates the importance of molecular surveillance in tracking AmpC-producing strains at general hospitals and emphasizes the need for epidemiological monitoring.

Conceptual bases for quantifying the role of the environment on gene evolution: the participation of positive selection and neutral evolution

To demonstrate that a given change in the environment has contributed to the emergence of a given genotypic and phenotypic shift during the course of evolution, one should ask to what extent such shifts would have occurred without environmental change. Of course, such tests are rarely practical but phenotypic novelties can still be correlated to genomic shifts in response to environmental changes if enough information is available. We surveyed and re-evaluated the published data in order to estimate the role of environmental changes on the course of species and genomic evolution. Only a few published examples clearly demonstrate a causal link between a given environmental change and the fixation of a genomic variant resulting in functional modification (gain, loss or alteration of function). Many others suggested a link between a given phenotypic shift and a given environmental change but failed to identify the underlying genomic determinant(s) and/or the associated functional consequence(s). The proportion of genotypic and phenotypic variation that is fixed concomitantly with environmental changes is often considered adaptive and hence, the result of positive selection, even though alternative causes, such as genetic drift, are rarely investigated. Therefore, the second aim herein is to review evidence for the mechanisms leading to fixation.

Dissemination of imipenem-resistant Acinetobacter baumannii strains carrying the ISAba1–bla OXA-23 genes in a Chinese hospital

An outbreak of 95 clinical infections with imipenem-resistant Acinetobacter baumannii in a Chinese hospital was investigated and the carbapenemase-encoding genes and their relationship with ISAba1 of these and a further 16 isolates recovered from the intensive care unit (ICU) environment were analysed. Almost all isolates were resistant to a wide range of antimicrobials; the lowest resistance rates were found for polymyxin E (17.1 %), cefoperazone/sulbactam (30.6 %) and ampicillin/sulbactam (67.6 %). Six pattern types defined by DNA macrorestriction patterns were distinguished among the clinical isolates with dissemination of pattern A (50 isolates) to patients in seven hospital units and pattern B (35 isolates) to eight units; the environmental isolates from ICUs were also of pattern A. All isolates were positive for the bla OXA-66 and bla OXA-23 genes. The OXA-23-encoding gene was located 34 bp downstream of ISAba1. No plasmids were detected and conjugal transfer of resistance was not demonstrated. The bla OXA-23 probe hybridized with 200 and 220 kb ApaI chromosomal fragments for type patterns A and B, respectively.

Sequencing and comparative genomic analysis of pK29, a 269-kilobase conjugative plasmid encoding CMY-8 and CTX-M-3 beta-lactamases in Klebsiella pneumoniae

A 269-kilobase conjugative plasmid, pK29, from a Klebsiella pneumoniae strain was sequenced. The plasmid harbors multiple antimicrobial resistance genes, including those encoding CMY-8 AmpC-type and CTX-M-3 extended-spectrum beta-lactamases in the common backbone of IncHI2 plasmids. Mechanisms for dissemination of the resistance genes are highlighted in comparative genomic analyses.

Identification of plasmid-mediated extended-spectrum and AmpC β-lactamases in Enterobacter spp. isolated from dogs

The genetic determinants involved in reduced susceptibility to third-generation cephalosporins and aztreonam were identified in ten canine Enterobacter isolates associated with opportunistic infections in three veterinary hospitals in Brisbane, Australia. All isolates were evaluated by a combination of phenotypic (broth microdilution and disc susceptibility, modified disc diffusion and IEF) and genotypic (PFGE, plasmid analysis, Southern blot hybridization, bacterial conjugation, PCR and sequencing) methods to investigate genetic relatedness and to identify plasmid-mediated resistance genes, in particular beta-lactamase genes responsible for extended-spectrum cephalosporin resistance. The ten canine isolates were genotypically diverse based on PFGE and belonged to either Enterobacter cloacae or Enterobacter hormaechei on the basis of 16S rRNA gene sequence analysis. Plasmid profiles were also diverse. Nine isolates contained a transmissible blaSHV-12-carrying plasmid (approximately 140 kb) that also conferred resistance to chloramphenicol, gentamicin, spectinomycin, tetracycline, trimethoprim and sulfonamides. In all plasmid-mediated extended-spectrum beta-lactamase (ESBL)-producing isolates including transconjugants, blaSHV-12 was shown to reside in a approximately 6.5 kb plasmid fragment. The remaining isolate that was not an ESBL producer possessed an AmpC beta-lactamase gene (blaCMY-2) on a approximately 93 kb transmissible plasmid. This plasmid did not contain any other antimicrobial resistance genes. Additional plasmid-mediated beta-lactamases identified in some isolates included bla(TEM) and blaOXA-10. This is the first report of canine Enterobacter isolates containing transmissible plasmid-mediated blaSHV-12 and blaCMY-2 resistance genes. Therefore, Enterobacter isolated from opportunistic infections in dogs may be an important reservoir of plasmid-mediated resistance genes, which could potentially be spread to other members of the Enterobacteriaceae.

Resistance of strains producing extended-spectrum β-lactamases and genotype distribution in China

OBJECTIVE

To investigate the resistance of Escherichia coli and Klebsiella pneumoniae producing extended-spectrum beta-lactamases (ESBLs) and the genotyping of ESBLs in China.

METHODS

MICs of 12 antibiotics against 50 strains (by random selection) of ESBLs-producing E. coli and K. pneumoniae were determined by E-test. The genotypes of ESBLs were analyzed by PCR, DNA sequencing and isoelectric focusing.

RESULTS

The susceptibility rate of 50 isolates was 100% in imipenem, 60%-80% in cefoperazone/sulbactam, ceftazidime and piperacillin/tazobactam, and lower in other antimicrobial agents tested. Only 6.0% of the isolates were sensitive to cefotaxime. Four hundred and forty-seven of 509 isolates had been confirmed the genotype of ESBLs. Four hundred and sixteen strains produced only one type of ESBLs, including CTX-M-14 (271 strains), CTX-M-3 (70 strains), CTX-M-24 (35 strains), CTX-M-22 (8 strains), CTX-M-15 (4 strains), CTX-M-9 (4 strains), CTX-M-28 (3 strains), CTX-M-12 (1 strain), CTX-M-13 (1 strain), CTX-M-27 (1 strain), CTX-M-29 (1 strain), SHV-12 (10 strains), SHV-5 (4 strains), SHV-2 (2 strains), and SHV-9 (1 strain). Thirty isolates carried two or three types of ESBLs, and producing CTX-M-14 and CTX-M-3 together were the most common type.

CONCLUSION

The resistance of E. coli and K. pneumonia producing ESBLs in China was a serious issue and CTX-M type ESBLs were the most common genotype. CTX-M-14 was the predominant genotype. Some isolates produced two or three ESBLs.

Dissemination of extended-spectrum beta-lactamase-producing Enterobacteriaceae in intensive care units of a medical center in Taiwan

The prevalence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in a tertiary hospital in Taiwan was assessed over a 16-month period. A total of 125 nonrepetitive ESBL-producing isolates of Enterobacter cloacae, Escherichia coli, and Klebsiella pneumoniae were available for investigation using molecular methods. Four predominant intensive care units (ICUs) were identified, and SHV-12 (59%), CTX-M- 3 (36%), and CTX-M-14 (14%) were the three most frequent ESBLs. SHV-12 was predominant among E. cloacae in the burn unit and K. pneumoniae in the other three chest medicine-related ICUs. CTX-M-3 was predominant among E. coli and K. pneumoniae in three other ICUs. The dissemination of ESBL-producing Enterobacteriaceae in four ICUs of a medical center in Taiwan is a consequence of the clonal dissemination of a few epidemic strains along with the horizontal transmission of resistance genes-carrying plasmids among bacterial organisms.

Integrons containing the VIM-2 metallo-beta-lactamase gene among imipenem-resistant Pseudomonas aeruginosa strains from different Chinese hospitals

A total of 140 nonrepetitive strains of imipenem-resistant Pseudomonas aeruginosa were isolated from five different Chinese hospitals. Fourteen isolates were confirmed to contain the VIM-2 metallo-beta-lactamase gene. Twelve isolates harbored two kinds of class 1 integron, containing both VIM-2- and aminoglycoside-resistant genes.

Combinatorial genetic evolution of multiresistance

The explosion in genetic information, whilst extending our knowledge, might not necessary increase our conceptual understanding on the complexities of bacterial genetics, or why some antibiotic resistant genotypes such as blaCTX-M-15 and blaVIM-2 appear to dominate. However, the information we have thus far suggests that clinical isolates have 'hijacked' plasmids, primarily built of backbone-DNA originating from environmental bacteria. Additionally, the combinatorial presence of other elements such as transposons, integrons, insertion sequence (IS) elements and the 'new' ISCR (IS common region) elements have also contributed to the increase in antibiotic resistance - an antibiotic resistant cluster composing four or five genes has become commonplace. In some instances, the presence of antibiotics themselves, such as fluoroquinolones, can mediate a bacterial SOS cell response, subsequently amplifying and/or augmenting the transfer of large genetic entities therefore, potentially promoting long-term detrimental effects.

ISCR elements: novel gene-capturing systems of the 21st century?

"Common regions" (CRs), such as Orf513, are being increasingly linked to mega-antibiotic-resistant regions. While their overall nucleotide sequences show little identity to other mobile elements, amino acid alignments indicate that they possess the key motifs of IS91-like elements, which have been linked to the mobility ent plasmids in pathogenic Escherichia coli. Further inspection reveals that they possess an IS91-like origin of replication and termination sites (terIS), and therefore CRs probably transpose via a rolling-circle replication mechanism. Accordingly, in this review we have renamed CRs as ISCRs to give a more accurate reflection of their functional properties. The genetic context surrounding ISCRs indicates that they can procure 5' sequences via misreading of the cognate terIS, i.e., "unchecked transposition." Clinically, the most worrying aspect of ISCRs is that they are increasingly being linked with more potent examples of resistance, i.e., metallo-beta-lactamases in Pseudomonas aeruginosa and co-trimoxazole resistance in Stenotrophomonas maltophilia. Furthermore, if ISCR elements do move via "unchecked RC transposition," as has been speculated for ISCR1, then this mechanism provides antibiotic resistance genes with a highly mobile genetic vehicle that could greatly exceed the effects of previously reported mobile genetic mechanisms. It has been hypothesized that bacteria will surprise us by extending their "genetic construction kit" to procure and evince additional DNA and, therefore, antibiotic resistance genes. It appears that ISCR elements have now firmly established themselves within that regimen.

Extended-spectrum beta-lactamases and plasmid-mediated AmpC enzymes among clinical isolates of Escherichia coli and Klebsiella pneumoniae from seven medical centers in Taiwan

Production of extended-spectrum beta-lactamases and plasmid-mediated AmpC enzymes was investigated among 291 Escherichia coli and 282 Klebsiella pneumoniae isolates that showed decreased susceptibilities to extended-spectrum cephalosporins from seven Taiwanese medical centers. CTX-M-type and SHV-type enzymes were the most prevalent extended-spectrum beta-lactamases. CMY-2-like and DHA-1-like beta-lactamases were the most prevalent AmpC-type enzymes.

Horizontal transfer of blaCMY-bearing plasmids among clinical Escherichia coli and Klebsiella pneumoniae isolates and emergence of cefepime-hydrolyzing CMY-19

Nine Escherichia coli and 5 Klebsiella pneumoniae clinical isolates resistant to various cephalosporins and cephamycins were identified in a Japanese general hospital between 1995 and 1997. All nine E. coli isolates and one K. pneumoniae isolate carried bla(CMY-9), while the other four K. pneumoniae isolates harbored a variant of bla(CMY-9), namely, bla(CMY-19). The pulsed-field gel electrophoresis patterns of the nine CMY-9-producing E. coli isolates were almost identical, suggesting their clonal relatedness, while those of the five K. pneumoniae isolates were divergent. Plasmid profiles, Southern hybridization, and conjugation assays revealed that the genes for the CMY-9 and the CMY-19 beta-lactamases were located on very similar conjugative plasmids in E. coli and K. pneumoniae. The genetic environment of bla(CMY-19) was identical to that of bla(CMY-9). A single amino acid substitution, I292S, adjacent to the H-10 helix region was observed between CMY-9 and CMY-19. This substitution was suggested to be responsible for the expansion of the hydrolyzing activity against several broad-spectrum cephalosporins, and this finding was consistent with the kinetic parameters determined with purified enzymes. These findings suggest that the bla(CMY-19) genes found in the four K. pneumoniae isolates might have originated from bla(CMY-9) gene following a point mutation and dispersed among genetically different K. pneumoniae isolates via a large transferable plasmid.

Distribution of a transposon-like element carrying blaCMY-2 among Salmonella and other Enterobacteriaceae

OBJECTIVES

The dissemination of cephamycin resistance in Enterobacteriaceae and its correlation with a transposon-like DNA element consisting of a specific tnpA-bla(CMY-2)-blc-sugE structure were investigated.

METHODS

A total of 140 enterobacterial isolates belonging to 17 species (10 genera) of Enterobacteriaceae phenotypically characterized as putative AmpC-producers were evaluated. The isolates were examined by PCR analysis, DNA-DNA hybridization and nucleotide sequencing.

RESULTS

The bla(CMY-2)-carrying element was detected in 34 isolates from 10 species (9 genera), including all 14 Salmonella and 4 Shigella isolates as well as 7 of the 10 Escherichia coli isolates tested. The remaining 9 isolates were from 112 isolates of the other 14 species tested. The genetic structure of the bla(CMY-2)-carrying element was identical in 29 isolates, while in 3 E. coli and 2 Citrobacter isolates an additional insertion sequence IS1 was found inserted at various nucleotide positions close to the 3' end, either within or downstream, of tnpA. In 12 of the 14 representative isolates examined, the bla(CMY-2)-carrying element was found inserted in the finQ gene of various-sized plasmids with highly conserved 8 bp direct repeats flanking the junction regions. Among the other 106 non-CMY-2-producing isolates, plasmid-mediated ampC genes were found only in one isolate of Enterobacter aerogenes which carried a bla(DHA-1)-like gene.

CONCLUSIONS

bla(CMY-2) is the most prevalent plasmid-mediated ampC gene among Enterobacteriaceae. All the bla(CMY-2) genes identified in the present study were associated with a specific transposon-like element that may be responsible for the spread of bla(CMY-2) among Enterobacteriaceae.

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.

Development of a multiplex PCR and SHV melting-curve mutation detection system for detection of some SHV and CTX-M beta-lactamases of Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae in Taiwan

Infection by extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae has been increasing in Taiwan. Accurate identification of the ESBL genes is necessary for surveillance and for epidemiological studies of the mode of transmission in the hospital setting. We describe herein the development of a novel system, which consists of a multiplex PCR to identify bla(SHV), bla(CTX-M-3)-like, and bla(CTX-M-14)-like genes and a modified SHV melting-curve mutation detection method to rapidly distinguish six prevalent bla(SHV) genes (bla(SHV-1), bla(SHV-2), bla(SHV-2a), bla(SHV-5), bla(SHV-11), and bla(SHV-12)) in Taiwan. Sixty-five clinical isolates, which had been characterized by nucleotide sequencing of the bla(SHV) and bla(CTX-M) genes, were identified by the system. The system was then used to genotype the ESBLs from 199 clinical isolates, including 40 Enterobacter cloacae, 68 Escherichia coli, and 91 Klebsiella pneumoniae, collected between August 2002 and March 2003. SHV-12 (80 isolates) was the most prevalent type of ESBL identified, followed in order of frequency by CTX-M-3 (65 isolates) and CTX-M-14 (36 isolates). Seventeen (9%) of the 199 clinical isolates harbored both SHV- and CTX-M-type ESBLs. In contrast to Enterobacter cloacae, the majority of which produced SHV-type ESBLs, E. coli and K. pneumoniae were more likely to possess CTX-M-type ESBLs. Three rare CTX-M types were identified through sequencing of the bla(CTX-M-3)-like (CTX-M-15) and bla(CTX-M-14)-like (CTX-M-9 and CTX-M-13) genes. The system appears to provide an efficient differentiation of ESBLs among E. coli, K. pneumoniae, and Enterobacter cloacae in Taiwan. Moreover, the design of the system can be easily adapted for similar purposes in areas where different ESBLs are prevalent.

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.

Expanded-spectrum beta-lactamase producing Klebsiella pneumoniae-related peritonitis in a patient on peritoneal dialysis

While hospitalized for pneumonia with ventilator-dependent respiratory failure, a 45-year-old man on continuous ambulatory peritoneal dialysis (CAPD) had nosocomial peritonitis secondary to infection by expanded spectrum beta-lactamase producing Klebsiella pneumoniae (ESBL-Kp). He was treated successfully with a 3-week course of intraperitoneal (IP) flomoxef therapy without subsequent relapse, loss of peritoneal catheter, ultrafiltration failure, or dialysis inadequacy. The International Consensus Panel recommends IP ceftazidime as the treatment of choice for CAPD patients suffering Klebsiella species-related peritonitis. However, the most appropriate form of IP antibiotic therapy and the outcomes for expanded-spectrum beta-lactamase (ESBL)-producing bacteria-related peritonitis for CAPD patients have not been established yet. Further, the ability to correctly report minimal inhibitory concentrations (MICs) of ceftazidime for ESBL bacteria in the resistant range varies between laboratories, making the diagnosis of ESBL-Kp-related CAPD peritonitis more complex and difficult. Thus, it appears reasonable to suggest that its incidence is probably underestimated and its significance ignored. The authors suggest that a 3-week IP treatment with flomoxef, a synthesized oxacephem, with loading and maintenance doses of 250 and 125 mg/L, respectively, is effective and safe for ESBL-Kp-related peritonitis in these patients. ESBL producing bacterial infection should be considered as a possible cause of overt CAPD-related peritonitis. Early detection of ESBLB pathogens and institution of effective antibiotic treatment may improve the prognosis.

Complexity of Klebsiella pneumoniae isolates resistant to both cephamycins and extended-spectrum cephalosporins at a teaching hospital in Taiwan

Among 99 clinical Klebsiella pneumoniae isolates resistant to cefoxitin and extended-spectrum cephalosporins, coexistence of AmpC (DHA-1, CMY-2, or CMY-8) and extended-spectrum beta-lactamases (CTX-M and/or SHV) was detected in a total of 35. The remainder produced AmpC (n = 42), extended-spectrum beta-lactamases (n = 9), metallo-beta-lactamases (n = 2), or none of these enzymes (n = 11). Phenotypic characteristics of these isolates were demonstrated.

Involvement of SHV-12 and SHV-2a encoding plasmids in outbreaks of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a Tunisian neonatal ward

Previous genotypic investigations of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae recovered in a Tunisian neonatal ward revealed the spread of two epidemic strains and a high number of genetically unrelated isolates. The aim of the present study was to determine the role of the dissemination of self-transferrable plasmids harboring bla genes in the outbreaks experienced by the ward. The 49 previously identified clinical isolates of ESBL-producing K. pneumoniae were examined for relationships between their enzymes and plasmids. Analysis of crude extracts by isoelectric focusing showed four beta-lactamase-activities at pI 8.2, 7.6, 6, and 5.4. Clinical isolates contained large plasmids that could be transferred by conjugation and transformation conferring resistance to expanded-spectrum cephalosporins. DNA amplification and sequencing were performed to confirm the identities of transferred beta-lactamases. Nucleotide sequence analysis of SHV-specific PCR products from six isolates identified two bla(SHV) genes corresponding to SHV derived ESBLs, SHV-12 and SHV-2a. PstI digestion of plasmid DNA from transformants revealed six restriction patterns. The occurrence of the prevalent plasmid pattern in both epidemic strains and unrelated isolates indicated that diffusion and endemic persistence of the bla(SHV-ESBL) genes in the ward were due to concomitant spread of epidemic strains and plasmid dissemination among unrelated strains.

Nosocomial and community-acquired Enterobacter cloacae bloodstream infection: risk factors for and prevalence of SHV-12 in multiresistant isolates in a medical centre

In a medical centre in northern Taiwan, 60 patients had bloodstream infection caused by Enterobacter cloacae from 1 January 2002 to 30 April 2003. Forty (66.7%) were nosocomial and 26 were caused by multiresistant isolates. Twenty patients died due to the infection. Central venous catheterization and mechanical ventilation were relative risks for nosocomial E. cloacae infection. Age and mechanical ventilation were risk factors for multiresistant E. cloacae infection. Mortality was associated with multiresistant isolates and polymicrobial infection. Pulsed-field gel electrophoresis (PFGE) analysis showed, the 26 multiresistant isolates comprised 12 different types, with type A predominating (12 isolates). Excluding the patients infected with PFGE type A, central venous catheterization was a relative risk for infection, and polymicrobial infection was a risk factor for mortality. All but one of the 26 multiresistant isolates had the extended-spectrum beta-lactamase SHV-12. TEM-1 and ampC beta-lactamase genes were also detected in 25 of the 26 multiresistant isolates. Southern blotting indicated that the SHV-12 gene was located on plasmids. Eleven of the 26 multiresistant isolates had minimum inhibitory concentrations (MIC) > or =16 mg/L for cefepime, which was reduced by the addition of sulbactam for most isolates, resulting in susceptibility. The combination of cefepime and sulbactam may be effective in the treatment of multiresistant E. cloacae bloodstream infection.