Survey and molecular genetics of SHV beta-lactamases in Enterobacteriaceae in Switzerland: two novel enzymes, SHV-11 and SHV-12

Extended-spectrum beta-lactamase-type SHV-12-producing Enterobacteriaceae causing septicemia in Tanzanian children: vectors for horizontal transfer of antimicrobial resistance

Septicemia caused by extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae was associated with high mortality in Tanzanian children. Conjugation experiments on the SHV-12-producing Enterobacteriaceae isolates showed that ESBL-encoding genes were transferred on large plasmids together with genes encoding resistance to aminoglycosides, resistance to ceftazidime, gentamicin, doxycycline, trimethoprim-sulfamethoxazole, and chloramphenicol.

Molecular characterization of extended-spectrum beta-lactamases in Enterobacteriaceae from patients of two hospitals in Saxony, Germany

Between January and September 2003, 39 isolates of the family Enterobacteriaceae with phenotypically positive Vitek 1 extended-spectrum beta-lactamase (ESBL) test results were collected, originating from patients of two hospitals in Saxony, Germany. Plasmid DNA was isolated and screened by PCR for the presence of genes encoding beta-lactamases of SHV, TEM and CTX-M types. To differentiate ESBL and non-ESBL among SHV and TEM genes, detailed analysis of PCR products was performed. Twenty-four strains carried SHV-2, SHV-5 or SHV-12 genes. In a further 11 strains a CTX-M gene was detected. The CTX-M genes could be affiliated to the CTX-M-1 and CTX-M-9 cluster by RFLP analysis. In the case of four Klebsiella oxytoca isolates, hyperproduction of the chromosomal beta-lactamase K1 was inferred, because genes of the above-mentioned types were not detected. The strains contained plasmid DNA between 45 and 160 kb in size. Common plasmid restriction patterns among SHV-5 producers provided evidence of horizontal spread. Twenty strains had a MIC for cefotaxime of ⩽4 mg l−1, 18 strains had the same MIC for ceftazidime, and nine strains had this MIC of >4 mg l−1 for both antibiotics. The ESBL phenotypes often coincided with ciprofloxacin or gentamicin resistance.

Occurrence of qnrA-positive clinical isolates in French teaching hospitals during 2002-2005

Bacteria harbouring the novel qnrA plasmid-mediated mechanism of quinolone resistance have been described in different countries, but the frequency of their occurrence has not been investigated. In total, 1,468 clinical isolates of Enterobacteriaceae with quinolone resistance or extended-spectrum beta-lactamase (ESBL) phenotypes were collected from eight teaching hospitals in France during 2002-2005 and screened for qnrA. Overall, 28 isolates (22 Enterobacter cloacae, three Klebsiella pneumoniae, one Citrobacter freundii, one Klebsiella oxytoca and one Proteus mirabilis) were positive for qnrA, representing 1.9% of all isolates, 3.3% of ESBL-producing isolates (22% of the E. cloacae isolates) and 0% of non-ESBL-producing isolates. The prevalence of qnrA among consecutive ESBL-producing isolates in 2004 from the eight hospitals was 2.8% (18/639). Of the qnrA-positive isolates, 100% were intermediately-resistant or resistant to nalidixic acid, and 75% to ciprofloxacin. Twenty-one of the 22 qnrA-positive E. cloacae isolates were obtained from two hospitals in the Paris area, and molecular typing and plasmid content analysis showed clonal relationships for five, three and two isolates, respectively. The qnrA genetic environment was similar to that of the In36 integron. The remaining two isolates had qnrA variants (30 and 29 nucleotide differences, respectively, compared with the original sequence) and an unknown genetic environment. The ESBL gene associated with qnrA was bla(SHV-12) in most of the isolates, but bla(PER-1) and bla(SHV-2a) were found in two isolates. In France, it appears that qnrA-positive isolates are predominantly E. cloacae isolates producing SHV-12, and may be associated with the dissemination of an In36-like integron.

Effects of phenotype and genotype on methods for detection of extended-spectrum-beta-lactamase-producing clinical isolates of Escherichia coli and Klebsiella pneumoniae in Norway

Consecutive clinical isolates of Escherichia coli (n = 87) and Klebsiella pneumoniae (n = 25) with reduced susceptibilities to oxyimino-cephalosporins (MICs > 1 mg/liter) from 18 Norwegian laboratories during March through October 2003 were examined for bla(TEM/SHV/CTX-M) extended-spectrum-beta-lactamase (ESBL) genes, oxyimino-cephalosporin MIC profiles, ESBL phenotypes (determined by the ESBL Etest and the combined disk and double-disk synergy [DDS] methods), and susceptibility to non-beta-lactam antibiotics. Multidrug-resistant CTX-M-15-like (n = 23) and CTX-M-9-like (n = 15) ESBLs dominated among the 50 ESBL-positive E. coli isolates. SHV-5-like (n = 9) and SHV-2-like (n = 4) ESBLs were the most prevalent in 19 ESBL-positive K. pneumoniae isolates. Discrepant ESBL phenotype test results were observed for one major (CTX-M-9) and several minor (TEM-128 and SHV-2/-28) ESBL groups and in SHV-1/-11-hyperproducing isolates. Negative or borderline ESBL results were observed when low-MIC oxyimino-cephalosporin substrates were used to detect clavulanic acid (CLA) synergy. CLA synergy was detected by the ESBL Etest and the DDS method but not by the combined disk method in SHV-1/-11-hyperproducing strains. The DDS method revealed unexplained CLA synergy in combination with aztreonam and cefpirome in three E. coli strains. The relatively high proportion of ESBL-producing E. coli organisms with a low ceftazidime MIC in Norway emphasizes that cefpodoxime alone or both cefotaxime and ceftazidime should be used as substrates for ESBL detection.

Evaluation of the new VITEK 2 extended-spectrum beta-lactamase (ESBL) test for rapid detection of ESBL production in Enterobacteriaceae isolates

Extended-spectrum beta-lactamases (ESBLs) are a large, rapidly evolving group of enzymes that confer resistance to oxyimino cephalosporins and monobactams and are inhibited by clavulanate. Rapid reliable detection of ESBL production is a prerequisite for successful infection management and for monitoring resistance trends and implementation of intervention strategies. We evaluated the performance of the new VITEK 2 ESBL test system (bioMérieux, Inc, Hazelwood, Mo.) in the identification of ESBL-producing Enterobacteriaceae isolates. We examined a total of 1,129 clinically relevant Enterobacteriaceae isolates (including 218 that had been previously characterized). The ESBL classification furnished by the VITEK 2 ESBL test system was concordant with that of the comparison method (molecular identification of beta-lactamase genes) for 1,121 (99.3%) of the 1,129 isolates evaluated. ESBL production was correctly detected in 306 of the 312 ESBL-producing organisms (sensitivity, 98.1%; positive predictive value, 99.3%). False-positive results emerged for 2 of the 817 ESBL-negative isolates (specificity, 99.7%; negative predictive value, 99.3%). VITEK 2 ESBL testing took 6 to 13 h (median, 7.5 h; mean +/- SD, 8.2 +/- 2.39 h). This automated short-incubation system appears to be a rapid and reliable tool for routine identification of ESBL-producing isolates of Enterobacteriaceae.

Cephalosporin resistance in Klebsiella pneumoniae from Nova Scotia, Canada

From 2116 Klebsiella pneumoniae strains isolated between January 2001 and December 2002 in Nova Scotia, Canada, 25 (1.18%) showed a reduced susceptibility to cefoxitin or extended-spectrum cephalosporins. Narrow-spectrum beta-lactamase genes (bla(SHV-11), bla(SHV-1), bla(SHV-26), bla(SHV-32), bla(SHV-36), and bla(SHV-40)) were the most prevalent. Four new variants were identified (bla(LEN-17), bla(OKP-B-13), bla(OKP-B-14), and bla(OKP-A-11)), representing the 1st description of bla(OKP) in the Americas. Among the extended-spectrum beta-lactamase (ESBL) genes, bla(SHV-2), bla(SHV2a), bla(SHV-12), and bla(CTX-M-15) were detected (ESBL prevalence of 0.14%). Nineteen strains were resistant to cefoxitin (MIC, 32 to >256 microg/mL). Nevertheless, an AmpC-like activity was detected in only 1 strain, which expressed CMY-2. The combined effects of narrow-spectrum beta-lactamase production and decreased or nonexpression of OmpK35/36 porins did not account for the cefoxitin resistance observed in some of these strains.

Identification and characterization of ceftriaxone resistance and extended-spectrum beta-lactamases in Malawian bacteraemic Enterobacteriaceae

OBJECTIVES

To enumerate and characterize extended-spectrum beta-lactamases (ESBLs) amongst ceftriaxone-resistant coliforms in Blantyre, Malawi, where third-generation cephalosporin use is currently highly restricted.

METHODS

Over the period April 2004-March 2005 all ceftriaxone-resistant isolates from blood cultures were examined for the presence of ESBLs. Isoelectric focusing was performed on enzyme extracts. PCR and DNA sequencing of amplicons were used to identify the underlying genetic determinants responsible for the ESBL phenotypes. Transferability of the ESBL phenotypes was tested by conjugation to a susceptible Escherichia coli J53.

RESULTS

Enterobacteriaceae were isolated from 1191 blood cultures, of which 19 (1.6%) were ceftriaxone resistant. Ten isolates (0.7% of all isolates) demonstrated an ESBL phenotype but only eight were characterized as three isolates were from the same patient. Genotypes SHV-11 (n = 1), SHV-12 (n = 3), SHV-27 (n = 1), TEM-63 (n = 2) and CTX-M-15 (n = 1) were detected. Plasmid transfer of the ESBL resistance phenotype was successful for all the isolates.

CONCLUSIONS

In a clinical setting of minimal cephalosporin usage there is already a diversity of ESBL genotypes. Increased use of cephalosporins in this setting is likely to result in a rapid expansion of ESBLs and their prevalence will need to be carefully monitored.

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.

Prevalence of extended-spectrum β-lactamases in isolates of the Enterobacter cloacae complex from German hospitals

In 2002, 119 isolates of the Enterobacter cloacae complex were collected randomly from 11 German laboratories nationwide. Antibiotic susceptibilities were tested by disk-diffusion tests according to CLSI guidelines, and MICs were determined using Etests. PCRs were performed to amplify all TEM and SHV, and most CTX-M and OXA beta-lactamase genes. PCR products were sequenced to identify the precise extended spectrum beta-lactamase (ESBL) types. Isoelectric focusing (IEF) and PM/PML Etests were used to confirm production of the respective ESBLs. According to susceptibility tests and CLSI criteria, 49 (40%) isolates were resistant to extended-spectrum cephalosporins. Seven (5.8%) isolates were positive in at least one of the PCR assays. Sequencing identified production of TEM-1 beta-lactamase genes by three (2.9%) isolates, and ESBL genes of the CTX-M and SHV beta-lactamase families by five (4.2%) isolates. IEF confirmed the production of beta-lactamases in the expected pI ranges of the respective ESBLs, and four of the five ESBL-producers were detected using the PM/PML Etest. All ESBL-producing isolates showed co-resistance to sulphonamides.

High-dose cefepime as an alternative treatment for infections caused by TEM-24 ESBL-producing Enterobacter aerogenes in severely-ill patients

This study evaluated retrospectively the efficacy of treatment with cefepime vs. a carbapenem, in combination with amikacin or ciprofloxacin, for seriously-ill patients infected with ESBL-producing Enterobacter aerogenes who were admitted to an intensive care unit. Forty-four episodes of infection were investigated in 43 patients: 21 treated with cefepime; 23 with a carbapenem. The two treatment groups did not differ statistically in terms of age, APACHE II scores, and infection sites, but the average duration of antibiotic exposure was significantly shorter in the cefepime group (8.5 days vs. 11.4 days; p 0.04). Clinical improvement was seen in 62% of patients receiving cefepime vs. 70% of patients receiving a carbapenem (p 0.59). Bacteriological eradication was achieved in 14% of patients receiving cefepime vs. 22% of patients receiving a carbapenem (p 0.76). The 30-day mortality rates related to infection were 33% in the cefepime group and 26% in the carbapenem group (p 0.44). Thus, outcome parameters did not differ significantly between the two groups. Nevertheless, a statistically significant increase in failure to eradicate ESBL-producing E. aerogenes was observed as the MICs of cefepime rose (p 0.017). Pulsed-field gel electrophoresis revealed three distinct clones, but one predominant clone harbouring the bla(TEM-24) gene was associated with most (42/44) of the episodes of infection. It was concluded that cefepime may be an alternative agent for therapy of severe infections caused by TEM-24 ESBL-producing E. aerogenes, although further studies are required to confirm these observations.

[Investigation of the new QNR-based mechanism of quinolone resistance among enterobacterial strains isolated in Henri-Mondor hospital 2002-2005]

AIM OF THE STUDY

To assess the prevalence of the novel plasmid-mediated resistance to quinolones in enterobacteria isolated in our hospital.

MATERIALS AND METHODS

We have screened 737 enterobacterial strains isolated in Henri-Mondor hospital between 2002 and 2005 for the presence of the qnr gene by PCR using specific primers. Among them, 282 had a phenotype in concordance with extended spectrum betalactamase (ESBL). Qnr-positive strains were phenotypically and genetically characterized, and epidemiological link between the cases was investigated.

RESULTS

Five qnr+ strains were described. The global prevalence was 0.7% but 5/282 among ESBL producing strains and 0/437 among quinolone-resistant enterobacteria non producing ESBL. The sequences of the PCR products were identical to qnrA in the environment of the integron In36. All the strains harboured also the ESBL SHV-12 gene. Transfer of qnr by conjugation raised quinolone MICs from 2 to 24 times. However clinical strains harboured a higher level of quinolone resistance and harboured also DNA gyrase and topoisomerase IV mutations. Two strains were epidemiologically related by molecular typing and contact tracing revealed that the patients have been previously hospitalized in the same tertiary care center.

CONCLUSION

We described the first investigation of qnr-positive strains in one hospital in France over 4 years. Although the qnr gene prevalence is low, nosocomial transmission is already shown and the transfer of the qnr containing integron among ESBL producing strains may predict future epidemic. Surveillance will be necessary to confirm this low prevalence rate of qnr in France.

Detection of a bla(SHV) extended-spectrum {beta}-lactamase in Salmonella enterica serovar Newport MDR-AmpC

Salmonella enterica serovar Newport MDR-AmpC expressing TEM-1b and extended-spectrum beta-lactamase SHV-12 was isolated from affected animals during an outbreak of salmonellosis that led to a 3-month closure of one of the largest equine hospitals in the United States.

Widespread transfer of resistance genes between bacterial species in an intensive care unit: implications for hospital epidemiology

A transferable plasmid encoding SHV-12 extended-spectrum beta-lactamase, TEM-116, and aminoglycoside resistance was responsible for two sequential clonal outbreaks of Enterobacter cloacae and Acinetobacter baumannii bacteria. A similar plasmid was present among isolates of four different bacterial species. Recognition of plasmid transfer is crucial for control of outbreaks of multidrug-resistant nosocomial pathogens.

Extended spectrum beta-lactamases among Gram-negative bacteria of nosocomial origin from an intensive care unit of a tertiary health facility in Tanzania

BACKGROUND

Resistance to third generation cephalosporins due to acquisition and expression of extended spectrum beta-lactamase (ESBL) enzymes among Gram-negative bacteria is on the increase. Presence of ESBL producing organisms has been reported to significantly affect the course and outcome of an infection. Therefore infections due to ESBL isolates continue to pose a challenge to infection management worldwide. The aim of this study was to determine the existence and to describe phenotypic and genotypic characteristics of ESBLs in an Intensive Care Unit (ICU) setting in Tanzania.

METHODS

Between October 2002 and April 2003, clinical information and samples were collected from patients suspected to have nosocomial infections in an Intensive Care Unit of a tertiary hospital in Tanzania. The isolates were identified, tested for antimicrobial susceptibility and analysed for presence of ESBL genes.

RESULTS

Thirty-nine Gram-negative bacteria were isolated from clinical samples of 39 patients. These isolates included 13 Escherichia coli, 12 Enterobacter spp, 5 Pseudomonas spp, 4 Proteus spp, 2 Klebsiella. pneumoniae, 2 Citrobacter freundii and 1 Chryseomonas luteola. Eleven (28.2%) of these isolates were ESBL producing. The ESBL genes characterised were SHV-12, SHV-28 and CTX-M-15. The ESBL producing isolates were more resistant to gentamicin and ciprofloxacin than non-ESBL producing isolates.

CONCLUSION

This study shows the presence of ESBL genes among Gram-negative bacteria in the ICU setting in Tanzania. There is a need to institute strict hospital infection control policy and a regular surveillance of resistance to antimicrobial agents.

Extended-spectrum-beta-lactamase-producing Enterobacteriaceae in Yaounde, Cameroon

Organisms producing extended-spectrum beta-lactamases (ESBLs) have been reported in many countries, but there is no information on the prevalence of ESBL-producing members of the family Enterobacteriaceae in Cameroon. A total of 259 Enterobacteriaceae strains were isolated between 1995 and 1998 from patients at the Yaounde Central Hospital in Cameroon. Enterobacterial isolates resistant to extended-spectrum cephalosporin and monobactam were screened for ESBL production by the double-disk (DD) synergy test. Thirty-one (12%) of these Enterobacteriaceae strains were shown to be positive by the DD synergy test, suggesting the presence of ESBLs. Resistance to oxyimino-cephalosporins and monobactams of 12 (38.7%) of the 31 strains-i.e., 6 Klebsiella pneumoniae, 4 Escherichia coli, 1 Citrobacter freundii, and 1 Enterobacter cloacae strain-was transferred to E. coli HK-225 by conjugation. Resistance to gentamicin, gentamicin plus trimethoprim-sulfamethoxazole, or trimethoprim-sulfamethoxazole was cotransferred into 6, 2, and 1 of these transconjugants, respectively. All 12 transconjugants were resistant to amoxicillin, piperacillin, all of the cephalosporins, and aztreonam but remained susceptible to cefoxitin and imipenem. Crude extracts of beta-lactamase-producing transconjugants were able to reduce the diameters of inhibition zones around disks containing penicillins, narrow- to expanded-spectrum cephalosporins or monobactams when tested against a fully susceptible E. coli strain but had no effect on such zones around cefoxitin, imipenem, and amoxicillin-clavulanate disks. The beta-lactamases produced by the 12 tranconjugants turned out to be SHV-12 by DNA sequencing. Therefore, the ESBL SHV-12 is described for the first time in Cameroon.

Novel spectinomycin/streptomycin resistance gene, aadA14, from Pasteurella multocida

A novel spectinomycin/streptomycin resistance gene, designated aadA14, was detected on the mobilizable 5,198-bp plasmid pCCK647 from Pasteurella multocida. The aadA14 gene encodes an aminoglycoside adenylyltransferase of 261 amino acids. Sequence comparisons revealed that the AadA14 protein showed less than 60% identity to the AadA proteins known so far.

Occurrence and regional distribution of SHV-type extended-spectrum beta-lactamases in Hungary

In order to determine the presence and geographical distribution of SHV-type extended-spectrum beta-lactamase genes among Enterobacteriaceae strains in Hungary, isolates from 25 microbiology laboratories throughout the country were collected between January 2002 and August 2003 and examined. Sequencing of the genes showed that SHV-5 and SHV-2a are the dominant SHV-types in extended-spectrum beta-lactamase-producing Enterobacteriaceae strains in this country. The SHV-2 gene, which is prevalent in many European countries, was not detected, but one isolate carried the SHV-12 gene. The results show that these genes are circulating among Enterobacteriaceae strains in Hungary and indicate that strict infection control measures are warranted in order to prevent their spread.

Molecular basis of resistance to trimethoprim, chloramphenicol and sulphonamides in Bordetella bronchiseptica

OBJECTIVES

To date, little is known about the molecular basis of antimicrobial resistance in Bordetella bronchiseptica, an important respiratory tract pathogen in pigs, dogs and cats. The aim of this study was to identify genes coding for trimethoprim resistance present in porcine B. bronchiseptica and to determine their localization, transferability and association with other resistance genes.

METHODS

Six B. bronchiseptica isolates with elevated MICs of trimethoprim were investigated by PCR for the presence of trimethoprim resistance genes and their association with class 1 integrons. The amplicons obtained were cloned and sequenced. Plasmid localization of these integrons was confirmed by transformation and conjugation. Isolates carrying the same integron were compared for their genetic relatedness by XbaI and SpeI pulsed-field gel electrophoresis (PFGE).

RESULTS

Five B. bronchiseptica isolates carried a class 1 integron with two gene cassettes, one carrying the trimethoprim resistance gene dfrA1 and the other the chloramphenicol resistance gene catB3. This integron was present on a common conjugative plasmid in four of the five isolates and on the chromosome in the remaining isolate. All five B. bronchiseptica isolates proved to be related on the basis of their PFGE patterns. Another isolate had a class 1 integron with a dfrB1 and a catB2 cassette on a structurally different conjugative plasmid. The sulphonamide resistance gene sul1 was detected in the 3'-conserved segment of both types of integrons.

CONCLUSIONS

This is the first report of trimethoprim, chloramphenicol and sulphonamide resistance genes and class 1 integrons in B. bronchiseptica isolates.

SHV-49, a novel inhibitor-resistant beta-lactamase in a clinical isolate of Klebsiella pneumoniae

A clinical strain of Klebsiella pneumoniae carried the bla(SHV-49) gene, encoding a novel inhibitor-resistant beta-lactamase of pI 7.6, derived from SHV-1 by the single substitution M69I. It also harbored a gene differing from bla(SHV-11) by four silent mutations and coding for a penicillinase. Both genes were chromosome located and might represent either a species-specific gene or an acquired resistance gene.

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.

Diversity and evolution of the class A chromosomal beta-lactamase gene in Klebsiella pneumoniae

We investigated the diversity of the chromosomal class A beta-lactamase gene in Klebsiella pneumoniae in order to study the evolution of the gene. A 789-bp portion was sequenced in a panel of 28 strains, representative of three phylogenetic groups, KpI, KpII, and KpIII, recently identified in K. pneumoniae and of different chromosomal beta-lactamase variants previously identified. Three groups of sequences were found, two of them corresponding to the families SHV (pI 7.6) and LEN (pI 7.1), respectively, and one, more heterogeneous, corresponding to a new family that we named OKP (for other K. pneumoniae beta-lactamase). Levels of susceptibility to ampicillin, cefuroxime, cefotaxime, ceftazidime, and aztreonam and inhibition by clavulanic acid were similar in the three groups. One new SHV variant, seven new LEN variants, and four OKP variants were identified. The OKP variants formed two subgroups based on nucleotide sequences, one with pIs of 7.8 and 8.1 and the other with pIs of 6.5 and 7.0. The nucleotide sequences of the housekeeping genes gyrA, coding for subunit A of gyrase, and mdh, coding for malate dehydrogenase, were also determined. Phylogenetic analysis of the three genes studied revealed parallel evolution, with the SHV, OKP, and LEN beta-lactamase families corresponding to the phylogenetic groups KpI, KpII, and KpIII, respectively. This correspondence was fully confirmed for 34 additional strains in PCR assays specific for the three beta-lactamase families. We estimated the time since divergence of the phylogenetic groups KpI and KpIII at between 6 and 28 million years, confirming the ancient presence of the beta-lactamase gene in the genome of K. pneumoniae.

Diversity and evolution of the class A chromosomal beta-lactamase gene in Klebsiella pneumoniae

We investigated the diversity of the chromosomal class A beta-lactamase gene in Klebsiella pneumoniae in order to study the evolution of the gene. A 789-bp portion was sequenced in a panel of 28 strains, representative of three phylogenetic groups, KpI, KpII, and KpIII, recently identified in K. pneumoniae and of different chromosomal beta-lactamase variants previously identified. Three groups of sequences were found, two of them corresponding to the families SHV (pI 7.6) and LEN (pI 7.1), respectively, and one, more heterogeneous, corresponding to a new family that we named OKP (for other K. pneumoniae beta-lactamase). Levels of susceptibility to ampicillin, cefuroxime, cefotaxime, ceftazidime, and aztreonam and inhibition by clavulanic acid were similar in the three groups. One new SHV variant, seven new LEN variants, and four OKP variants were identified. The OKP variants formed two subgroups based on nucleotide sequences, one with pIs of 7.8 and 8.1 and the other with pIs of 6.5 and 7.0. The nucleotide sequences of the housekeeping genes gyrA, coding for subunit A of gyrase, and mdh, coding for malate dehydrogenase, were also determined. Phylogenetic analysis of the three genes studied revealed parallel evolution, with the SHV, OKP, and LEN beta-lactamase families corresponding to the phylogenetic groups KpI, KpII, and KpIII, respectively. This correspondence was fully confirmed for 34 additional strains in PCR assays specific for the three beta-lactamase families. We estimated the time since divergence of the phylogenetic groups KpI and KpIII at between 6 and 28 million years, confirming the ancient presence of the beta-lactamase gene in the genome of K. pneumoniae.

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.

SHV-12-like extended-spectrum-beta-lactamase-producing strains of Salmonella enterica serotypes Babelsberg and Enteritidis isolated in France among infants adopted from Mali

From December 2002 to June 2003, 14 cultures of Salmonella enterica serotype Babelsberg and 6 cultures of serotype Enteritidis, isolated in France from internationally adopted children, were identified at the French National Reference Center for Salmonella. All serotype Babelsberg isolates were related, as determined by pulsed-field gel electrophoresis, and all serotype Enteritidis strains displayed the same phage type. All serotype Enteritidis and seven serotype Babelsberg isolates produced an SHV-12-like extended-spectrum beta-lactamase as determined by sequencing of PCR products and by isoelectrofocusing. Some serotype Enteritidis isolates exhibited additional antimicrobial resistance (aminoglycosides, tetracycline, chloramphenicol, sulfonamides, and trimethoprim). Our investigation indicated that these Salmonella isolates were certainly acquired in the same orphanage in Bamako, Mali, before the children were adopted by French families. An inappropriate use of ceftriaxone was probably the cause of the emergence of such strains. There is an urgent need to determine the origin of the contamination and to introduce adequate antibiotic protocols into this orphanage to prevent further transmission and dissemination. Screening for infections and follow-up, adapted to the origin of the internationally adopted children, should be recommended.

Complex endemic situation regarding extended-spectrum beta-lactamase-producing Klebsiella pneumoniae in a hospital in Slovenia

The first detailed epidemiological study of extended-spectrum beta-lactamase (ESBL)-producing organisms identified in Slovenia was carried out. It was performed on a group of 40 Klebsiella pneumoniae isolates that were randomly selected from all putative ESBL producers of this species recovered in a large hospital in Celje in 1997-2001. At least three different ESBLs, SHV-2, -5, and -12, were produced by the isolates and these enzymes seem to be common in nosocomial Enterobacteriaceae populations in countries of the region (e.g., Italy, Hungary, Croatia). The analysis revealed a complex epidemiology of the organisms, illustrated mostly by their high clonal variety but also by the diversity of their beta-lactamase and plasmid content, mating capability, and antimicrobial susceptibility. Although some cases of a 'fresh' dissemination of strains or plasmids could be identified, the overall situation should be described rather as endemic, and its complexity may be in part attributed to the late introduction of the ESBL detection procedure to the hospital.

Molecular epidemiology of extended-spectrum beta-lactamases produced by clinical isolates in a university hospital in Greece: detection of SHV-5 in Pseudomonas aeruginosa and prevalence of SHV-12

To assess the nature and diversity of various types of SHV and TEM derivatives in our hospital a survey was conducted. Sixty-seven extended-spectrum beta-lactamases (ESBL)-producing nosocomial pathogens, isolated over a 12-month period, were analyzed by means of PCR and direct sequencing. SHV-5 was the predominant ESBL found in our region (38 strains). Other less frequent variants included SHV-2 and SHV-12 with two and three isolates, respectively. For the first time, an outbreak of 11 Pseudomonas aeruginosa producing SHV-5 was encountered. All blaTEM-positive strains carried the non-ESBL TEM-1. The incidence of non-SHV non-TEM ESBLs was remarkably high as almost one out of three isolates harbored such an ESBL. The epidemiological and clinical impact of these findings must be carefully investigated and interpreted.

Extended-spectrum beta-lactamases in Ireland, including a novel enzyme, TEM-102

Organisms producing extended-spectrum beta-lactamases (ESBLs) have been reported in many countries, but there is no information on the prevalence of ESBL-producing members of the family Enterobacteriaceae in Ireland. A total of 925 isolates of ampicillin-resistant members of the Enterobacteriaceae were received from six hospitals in Ireland over a 3-year period from September 1996 to September 1999. Isolates were screened for ESBL production by the double-disk diffusion (DDD) method. DDD-positive isolates that were (i) confirmed as ESBL producers by National Committee for Clinical Laboratory Standards (NCCLS) confirmatory testing and (ii) susceptible to cefoxitin by disk diffusion were considered ESBL producers. By these criteria, 27 (3%) of the ampicillin-resistant members of the Enterobacteriaceae studied were categorized as ESBL producers. Molecular typing suggested that some intra- and interhospital spread of ESBL-producing isolates had occurred. DNA sequencing of amplified bla(TEM) and bla(SHV) genes resulted in the detection of a novel bla(TEM) ESBL gene, bla(TEM-102) in two isolates (Klebsiella pneumoniae and Enterobacter cloacae) received from the same hospital but isolated from different patients. The study suggests dissemination of ESBL-producing bacteria within the health care system in Ireland and emphasizes the need for measures to control such spread.

Detection of CMY-2, CTX-M-14, and SHV-12 beta-lactamases in Escherichia coli fecal-sample isolates from healthy chickens

Genes encoding the CMY-2, CTX-M-14, and SHV-12 beta-lactamases were detected in three of five Escherichia coli isolates from fecal samples from healthy chickens which showed resistance or diminished susceptibility to extended-spectrum cephalosporins. A -42 mutation at the promoter region of the ampC gene was detected in the other two isolates.

Infection with an extended-spectrum beta-lactamase-producing strain of Serratia marcescens following tongue reconstruction

We report a case of postsurgical wound infection of polymicrobial etiology caused by Serratia marcescens and Pseudomonas aeruginosa following the use of a radial forearm free flap for oncological tongue reconstruction. S. marcescens was a producer of SHV-12 extended-spectrum beta-lactamase (ESBL). This is the first report from India of this ESBL. S. marcescens and P. aeruginosa were resistant to the empirical perioperative antibiotics administered. Delay in the recognition of the type of infection and in the institution of appropriate therapy resulted in total loss of the free flap.

Clinical isolates of Enterobacteriaceae producing extended-spectrum beta-lactamases: prevalence of CTX-M-3 at a hospital in China

The prevalence of extended-spectrum beta-lactamase-producing strains was demonstrated in 5 of 44 (11.4%) Escherichia coli, 17 of 43 (39.5%) Klebsiella pneumoniae, 3 of 50 (6.0%) Enterobacter cloacae, and 2 of 25 (8.0%) Citrobacter freundii strains at a teaching hospital in China. Nineteen of these 27 strains expressed CTX-M-3 beta-lactamase (pI 8.6). A subset of the clinical isolates expressing the CTX-M-3 enzyme, tested by pulsed-field gel electrophoresis, revealed multiple clones. Five isolates expressed a novel enzyme, SHV-43 (pI 8.0), which had two substitutions (Leu113Phe and Thr149Ser) compared with SHV-1.

Transferable plasmid mediating resistance to multiple antimicrobial agents in Klebsiella pneumoniae isolates in Greece

OBJECTIVE

To investigate the underlying resistance mechanisms in 10 Klebsiella pneumoniae isolates.

METHODS

Ten K. pneumoniae strains according to distinct bacteriocin typing and REP-PCR, were examined for their plasmid content, their ability to transfer their resistance to aminoglycosides and third-generation cephalosporins, and their production of aminoglycoside-modifying enzymes and beta-lactamases.

RESULTS

Transfer of resistance to the above-mentioned antibiotics as well as to co-trimoxazole and tetracycline in Escherichia coli strain RC 85 at a frequency of 5-106 was achieved for all strains by conjugation. Similar strains harbor a self-transferable multiresistant plasmid (80 kb) with similar EcoRI and HindIII restriction patterns. This plasmid encodes an extended-spectrum beta-lactamase which confers high-level resistance to third-generation cephalosporins and aztreonam. It produces SHV-5 beta-lactamase, as demonstrated by isoelectric focusing and DNA sequencing. Aminoglycoside resistance was co-transferred, and AAC(6')-I, mediating resistance to gentamicin, tobramycin, netilmicin and amikacin, and AAC(3)-I, mediating resistance to gentamicin and sisomycin, were encoded in all isolates and their transconjugants, while APH(3')-I, mediating resistance to kanamycin and neomycin, was encoded in seven strains.

CONCLUSIONS

It appears that a multiresistant transferable plasmid encoding the SHV-5 beta-lactamase, causing unusually high resistance to ceftazidime and aztreonam, and the combination AAC(6')-I + AAC(3)-I of acetylating enzymes causing, also resistance to all clinically available aminoglycosides, is established in K. pneumoniae in Greece.

Three cefotaximases, CTX-M-9, CTX-M-13, and CTX-M-14, among Enterobacteriaceae in the People's Republic of China

Of 15 extended-spectrum beta-lactamase (ESBL)-producing isolates of the family Enterobacteriaceae collected from the First Municipal People's Hospital of Guangzhou, in the southern part of the People's Republic of China, 9 were found to produce CTX-M ESBLs, 3 produced SHV-12, and 3 produced both CTX-M and SHV-12. Eleven isolates produced either TEM-1B or SHV-11, in addition to an ESBL. Nucleotide sequence analysis of the 12 isolates carrying bla(CTX-M) genes revealed that they harbored three different bla(CTX-M) genes, bla(CTX-M-9) (5 isolates), bla(CTX-M-13) (1 isolate), and bla(CTX-M-14) (6 isolates). These genes have 98% nucleotide homology with bla(Toho-2). The bla(CTX-M) genes were carried on plasmids that ranged in size from 35 to 150 kb. Plasmid fingerprints and pulsed-field gel electrophoresis showed the dissemination of the bla(CTX-M) genes through transfer of different antibiotic resistance plasmids to different bacteria, suggesting that these resistance determinants are highly mobile. Insertion sequence ISEcp1, found on the upstream region of these genes, may be involved in the translocation of the bla(CTX-M) genes. This is the first report of the occurrence of SHV-12 and CTX-M ESBLs in China. The presence of strains with these ESBLs shows both the evolution of bla(CTX-M) genes and their dissemination among at least three species of the family Enterobacteriaceae, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae, isolated within a single hospital. The predominance of CTX-M type enzymes seen in this area of China appears to be similar to that seen in South America but is different from those seen in Europe and North America, suggesting different evolutionary routes and selective pressures. A more comprehensive survey of the ESBL types from China is urgently needed.

Identification and minisequencing-based discrimination of SHV beta-lactamases in nosocomial infection-associated Klebsiella pneumoniae in Brisbane, Australia

Extended-spectrum beta-lactamases (ESBLs) are active against oxyimino cephalosporins and monobactams. Twenty-one Klebsiella pneumoniae isolates obtained between 1991 and 1995 at the Princess Alexandra Hospital in Brisbane, Australia, were subject to amplification and sequencing of the SHV beta-lactamase-encoding genes. Thirteen strains were phenotypically ESBL positive. Of these, six strains carried the blaSHV-2a gene and seven strains carried the blaSHV-12 gene. Eight strains were phenotypically ESBL negative. Of these, seven strains carried the non-ESBL blaSHV-11 gene and one strain carried the non-ESBL blaSHV-1 gene. There was complete correspondence between the ESBL phenotype and the presence or absence of an ESBL-encoding gene(s). In addition, it was determined that of the 13 ESBL-positive strains, at least 4 carried copies of a non-ESBL-encoding gene in addition to the blaSHV-2a or blaSHV12 gene. A minisequencing-based assay was developed to discriminate the different SHV classes. This technique, termed "first-nucleotide change," involves the identification of the base added to a primer in a single-nucleotide extension reaction. The assay targeted polymorphisms at the first bases of codons 238 and 240 and reliably discriminated ESBL-positive strains from ESBL-negative strains and also distinguished strains carrying blaSHV-2a from strains carrying blaSHV-12. In addition, this method was used to demonstrate an association between the relative copy numbers of blaSHV genes in individual strains and the levels of antibiotic resistance.

Molecular characterization of extended-spectrum beta-lactamases produced by nosocomial isolates of Enterobacteriaceae from an Italian nationwide survey

Extended-spectrum beta-lactamases (ESBLs) are widespread in hospital settings worldwide. The present investigation was undertaken to assess the distribution and prevalence of ESBLs belonging to the TEM and SHV families in 448 ESBL-producing clinical isolates of Enterobacteriaceae collected from 10 different Italian hospitals. The natures of TEM and SHV determinants were identified by direct sequencing of PCR-amplified genes. TEM-52 and SHV-12 were the most common variants, and they were found in most hospitals and in several different species. Other less frequent variants included TEM-5, TEM-12, TEM-15, TEM-19, TEM-20, TEM-24, TEM-26, TEM-43, TEM-60, TEM-72, TEM-87, SHV-2a, SHV-5, and SHV-11. Proteus mirabilis was the most common producer of TEM-type ESBLs, while Klebsiella pneumoniae was the most common producer of SHV-type ESBLs. The distribution of TEM- and SHV-type ESBL variants in Enterobacteriaceae from Italian hospitals exhibited notable differences from those from other geographical settings.

Evolution and epidemiology of extended-spectrum beta-lactamases (ESBLs) and ESBL-producing microorganisms

The rapid and irrepressible increase in antimicrobial resistance of pathogenic bacteria that has been observed over the last two decades is widely accepted to be one of the major problems of human medicine today. Several aspects of this situation are especially worrying. There are resistance mechanisms that eliminate the use of last-choice antibiotics in the treatment of various kinds of infection. Many resistance mechanisms that emerge and spread in bacterial populations are those of wide activity spectra, which compromise all or a majority of drugs belonging to a given therapeutic group. Some mechanisms of great clinical importance require specific detection procedures, as they may not confer clear resistance in vitro on the basis of the interpretive criteria used in standard susceptibility testing. Finally, multiple mechanisms affecting the same and/or different groups of antimicrobials coexist and are even co-selected in more and more strains of pathogenic bacteria. The variety of beta-lactamases with wide spectra of substrate specificity illustrates very well all the phenomena mentioned above. Being able to hydrolyze the majority of beta-lactams that are currently in use, together they constitute the most important resistance mechanism of Gram-negative rods. Three major groups of these enzymes are usually distinguished, class C cephalosporinases (AmpC), extended-spectrum beta-lactamases (ESBLs) and different types of beta-lactamases with carbapenemase activity, of which the so-called class B metallo-beta-lactamases (MBLs) are of the greatest concern. This review is focused on various aspects of the evolution and epidemiology of ESBLs; it does not cover the problems of ESBL detection and clinical relevance of infections caused by ESBL-producing organisms.

SHV-1 beta-lactamase is mainly a chromosomally encoded species-specific enzyme in Klebsiella pneumoniae

The nature of the SHV-1 beta-lactamase gene was analyzed in 97 epidemiologically unrelated Klebsiella pneumoniae strains isolated from clinical samples. beta-Lactamase bands that focused at a pI of 7.6 (SHV-1-type) in 74 strains, at a pI of 7.1 (LEN-1-type) in 13 strains, and at a pI of 5.4 (TEM-1-type) in 10 strains were detected by analytical isoelectric focusing (IEF). Among the 74 SHV-1-producing strains, 40 had, in addition to the pI 7.6 band, an additional band on IEF: 20 had a band with a pI of 7.1 and 20 had a band with a pI of 5.4. Most of the 74 SHV-1-producing strains (76.7%) carried plasmids. Transfer of beta-lactam resistance by conjugation was possible in only 9.3% of the strains tested. SHV-1 gene-specific PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the chromosomal DNA was positive for 93 of the 97 strains and negative for only 4 of the 10 samples with K. pneumoniae TEM-1 producers. In an attempt to approximate the location of the SHV gene locus by endonuclease restriction analysis, RFLP analysis with Southern blotting of chromosomal DNA with a labeled SHV-1 fragment as a probe was used to study the 97 strains. A trial with EcoRI showed at least one positive hybridization band for 96 strains; two bands were detected for 8 strains. The hybridization was negative for only one TEM-1 beta-lactamase-producing strain. DNA sequence analysis showed no differences in promoter regions or extra stop-triplet sequences; only point mutations determined different allelic variants. The novel SHV-type variants are designated SHV-32 and SHV-33. As a result of the RFLP and sequencing analyses, it can be postulated that the loci for SHV-1 and LEN-1 genes are arranged in tandem. Our results strongly support the hypothesis that the ancestor of the SHV-1 beta-lactamase originated from the K. pneumoniae chromosome.

Real-time PCR and melting curve analysis for reliable and rapid detection of SHV extended-spectrum beta-lactamases

Extended-spectrum beta-lactamases (ESBLs), e.g., ESBLs of the TEM or SHV type, compromise the efficacies of expanded-spectrum cephalosporins. An SHV non-ESBL that hydrolyzes only narrow-spectrum cephalosporins can be converted into an SHV ESBL through substitutions at three amino acid positions, 179, 238, or 238--240. In order to improve detection of SHV ESBLs, a novel method, based on real-time PCR monitored with fluorescently labeled hybridization probes and followed by melting curve analysis, was developed. It is able to (i) detect bla(SHV) genes with high degrees of sensitivity and specificity, (ii) discriminate between bla(SHV non-ESBL) and bla(SHV ESBL), and (iii) categorize the SHV ESBL producers into three phenotypically relevant subgroups. This method, termed the SHV melting curve mutation detection method, represents a powerful tool for epidemiological studies with SHV ESBLs. It even has the potential to be used in the diagnostic microbiology laboratory, because up to 32 clinical isolates can be processed in less than 1 h by starting with just a few bacterial colonies.

Characterization of clinical isolates of Klebsiella pneumoniae from 19 laboratories using the National Committee for Clinical Laboratory Standards extended-spectrum beta-lactamase detection methods

Extended-spectrum beta-lactamases (ESBLs) are enzymes found in gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. In 1999, the National Committee for Clinical Laboratory Standards (NCCLS) published methods for screening and confirming the presence of ESBLs in Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli. To evaluate the confirmation protocol, we tested 139 isolates of K. pneumoniae that were sent to Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) from 19 hospitals in 11 U.S. states. Each isolate met the NCCLS screening criteria for potential ESBL producers (ceftazidime [CAZ] or cefotaxime [CTX] MICs were > or =2 microg/ml for all isolates). Initially, 117 (84%) isolates demonstrated a clavulanic acid (CA) effect by disk diffusion (i.e., an increase in CAZ or CTX zone diameters of > or =5 mm in the presence of CA), and 114 (82%) demonstrated a CA effect by broth microdilution (reduction of CAZ or CTX MICs by > or =3 dilutions). For five isolates, a CA effect could not be determined initially by broth microdilution because of off-scale CAZ results. However, a CA effect was observed in two of these isolates by testing cefepime and cefepime plus CA. The cefoxitin MICs for 23 isolates that failed to show a CA effect by broth microdilution were > or =32 microg/ml, suggesting either the presence of an AmpC-type beta-lactamase or porin changes that could mask a CA effect. By isoelectric focusing (IEF), 7 of the 23 isolates contained a beta-lactamase with a pI of > or =8.3 suggestive of an AmpC-type beta-lactamase; 6 of the 7 isolates were shown by PCR to contain both ampC-type and bla(OXA) genes. The IEF profiles of the remaining 16 isolates showed a variety of beta-lactamase bands, all of which had pIs of < or =7.5. All 16 isolates were negative by PCR with multiple primer sets for ampC-type, bla(OXA), and bla(CTX-M) genes. In summary, 83.5% of the K. pneumoniae isolates that were identified initially as presumptive ESBL producers were positive for a CA effect, while 5.0% contained beta-lactamases that likely masked the CA effect. The remaining 11.5% of the isolates studied contained beta-lactamases that did not demonstrate a CA effect. An algorithm based on phenotypic analyses is suggested for evaluation of such isolates.

Discrimination of SHV beta-lactamase genes by restriction site insertion-PCR

Restriction site insertion-PCR (RSI-PCR) is a simple, rapid technique for detection of point mutations. This technique exploits primers with one to three base mismatches near the 3' end to modulate a restriction site. We have developed this technique to identify described mutations of the bla(SHV) genes for differentiation of SHV variants that cannot be distinguished easily by other techniques. To validate this method, eight standard strains were used, each producing a different SHV beta-lactamase: SHV-1, SHV-2, SHV-3, SHV-4, SHV-5, SHV-6, SHV-8, and SHV-18. Mismatch primers were designed to detect mutations affecting amino acids at positions 8 (SspI), 179 (HinfI), 205 (PstI), 238 (Gly-->Ala) (BsrI), and 240 (NruI) of bla(SHV) genes. All amplimers of the bla(SHV) genes used in this study yielded the predicted restriction endonuclease digestion products. In addition, this study also makes theoretical identification of bla(SHV-6), bla(SHV-8), and 12 novel bla(SHV) variants using the PCR-restriction fragment length polymorphism (RFLP) technique possible. By using a combination of PCR-RFLP and RSI-PCR techniques, up to 27 SHV variants can now be distinguished rapidly and reliably. These simple techniques are readily applied to epidemiological studies of the SHV beta-lactamases and may be extended to the characterisation of other resistance determinants.

SHV-type extended-spectrum beta-lactamase in a Shigella flexneri clinical isolate

A Shigella flexneri isolate resistant to oxyimino-cephalosporins was recovered from a stool sample of a 16 month-old Algerian child hospitalized in Paris, France. This isolate harboured an SHV-2 beta-lactamase gene located on a c. 80 kb self-transferable plasmid. This is the first report of an Ambler class A extended-spectrum beta-lactamase from Shigella spp.

Comparison of five different methods for detection of SHV extended-spectrum beta-lactamases

Five different methods for detection of different types of SHV extended-spectrum beta-lactamases (ESBL) were compared: minimum inhibitory concentration (MIC) determination of beta-lactam with and without clavulanic acid, double-disk synergy test (DDST), inhibitor potentiated disk diffusion test (IPDDT), three-dimensional test (TDT) and PCR/Nhe I test. MIC determination of beta-lactam with and without clavulanic acid was the most sensitive method regardless of the type of beta-lactamase. However the specificity of this method was a little above 90%. IPDDT turned out to be a very sensitive method too but it lacks specificity because 26.9% of ceftazidime sensitive strains (putative ESBL negative), gave a positive result. It is important to put all four disks on the plate because ceftazidime and aztreonam were more sensitive indicators for SHV-5 and SHV-12 beta-lactamase producers while cefotaxime and ceftriaxone were more reliable in detecting SHV-2 beta-lactamase producers. The DDST detected all SHV-5 and SHV-12 beta-lactamase producers and 95.2% of SHV-2, so it was less sensitive than MIC determination but was highly specific, since there were no false negative results observed. The sensitivity of DDST can be improved by using all four disks and placing them at the smaller distance from the central disk (2.5 cm). The TDT was the least sensitive method, particularly for SHV-5 and SHV-12 beta-lactamase producers. The PCR/Nhe I test for detection of ESBL blaSHV genes is a highly sensitive and specific method but it is rather laborious and thus not very practical for use in routine clinical laboratories. Nevertheless it has potential to serve as the gold standard in epidemiological investigations on ESBLs. According to the results of this investigation MIC determination of beta-lactam with and without clavulanic acid, even if only one antibiotic is used and the PCR/Nhe I tests are the most reliable methods for detection of SHV ESBLs.

Occurrence and transferability of beta-lactam resistance in Enterobacteriaceae isolated in Children's University Hospital in Bratislava

Occurrence and transferability of beta-lactam resistance in 30 multi-resistant Escherichia coli, Klebsiella spp., Enterobacter spp., Pantoea agglomerans, Citrobacter freundii and Serratia marcescens strains isolated from children between 0 and 3 years of age is presented. The strains were resistant to ampicillin (30), cefoxitin (22), cefotaxime (30), ceftriaxone (30), ceftazidime (30) and aztreonam (28), but susceptible to cefepime (30) and imipenem (26). Twenty-eight of 30 isolates possessed a transferable resistance confirmed by conjugation and isolation of 79-89-kb plasmids. The beta-lactam resistance was due to production of beta-lactamases and ceftazidime proved to be stronger beta-lactamase inductor than ceftriaxone. Twenty-five clinical isolates expressed transferable extended spectrum beta-lactamases, and chromosomally encoded AmpC beta-lactamase.

Molecular analysis of tetracycline resistance in Salmonella enterica subsp. enterica serovars Typhimurium, enteritidis, Dublin, Choleraesuis, Hadar and Saintpaul: construction and application of specific gene probes

A total of 65 epidemiologically unrelated tetracycline-resistant isolates of the six Salmonella enterica subsp. enterica (Salm.) serovars Dublin, Choleraesuis, Typhimurium, Enteritidis, Hadar and Saintpaul were investigated for the presence of tetracycline resistance genes. For this, specific gene probes of the tetracycline resistance genes (tet) of the hybridization classes A, B, C, D, E and G were constructed by cloning PCR-amplified internal segments of the respective tet structural genes. These gene probes were sequenced and used in hybridization experiments with plasmid DNA or endonuclease digested whole cell DNA as targets. Only tet(A) genes were detected on plasmids in all Salm. Dublin isolates as well as in single isolates of Salm. Choleraesuis and Salm. Typhimurium. Genes of the hybridization classes B, C, D and G, but also in some cases those of class A, were located in the chromosomal DNA of the corresponding Salmonella isolates. Restriction fragment length polymorphisms (RFLPs) of tet gene carrying fragments were detected in chromosomally tetracycline-resistant isolates. These RFLPs might represent valuable additional tools for the identification and characterization of tetracycline-resistant Salmonella isolates.

Discriminatory detection of extended-spectrum beta-lactamases by restriction fragment length dimorphism-polymerase chain reaction

Plasmid-mediated resistance mechanisms to beta-lactams, comprising mostly extended-spectrum beta-lactamase (ESBL) production, lead to resistance against even the most recently developed beta-lactams in enterobacteria, which is now a serious threat to antibiotic therapy. In this work, the diagnostic ability of the restriction fragment length dimorphism (RFLD)-polymerase chain reaction (PCR) method in clinical samples was evaluated. Nine newly designed primer pairs were used to differentiate the genes encoding TEM-1a, SHV-12, MOX-1, MIR-1 and Toho-1 beta-lactamases. The RFLD-PCR was carried out successfully and these genes were differentiated by the sizes of their PCR product. This discriminatory detection of the genes was also confirmed by digestion with unique restriction enzyme sites and sequencing of the PCR products. The fragment sizes of PCR products digested with the enzymes were identical to the sizes calculated from nucleotide sequences of five beta-lactamase genes deposited in EMBL, GenBank and/or DDBJ databases and the sequences were also identical. In conclusion, the method and newly designed primers applied in this work can differentiate the ESBLs rapidly and effectively.

Characterization of the extended-spectrum beta-lactamase reference strain, Klebsiella pneumoniae K6 (ATCC 700603), which produces the novel enzyme SHV-18

Klebsiella pneumoniae K6 (ATCC 700603), a clinical isolate, is resistant to ceftazidime and other oxyimino-beta-lactams. A consistent reduction in the MICs of oxyimino-beta-lactams by at least 3 twofold dilutions in the presence of clavulanic acid confirmed the utility of K. pneumoniae K6 as a quality control strain for extended-spectrum beta-lactamase (ESBL) detection. Isoelectric-focusing analysis of crude lysates of K6 demonstrated a single beta-lactamase with a pI of 7.8 and a substrate profile showing preferential hydrolysis of cefotaxime compared to ceftazidime. PCR analysis of total bacterial DNA from K6 identified the presence of a bla(SHV) gene. K6 contained two large plasmids with molecular sizes of approximately 160 and 80 kb. Hybridization of plasmid DNA with a bla(SHV)-specific probe indicated that a bla(SHV) gene was encoded on the 80-kb plasmid, which was shown to transfer resistance to ceftazidime in conjugal mating experiments with Escherichia coli HB101. DNA sequencing of this bla(SHV)-related gene revealed that it differs from bla(SHV-1) at nine nucleotides, five of which resulted in amino acid substitutions: Ile to Phe at position 8, Arg to Ser at position 43, Gly to Ala at position 238, and Glu to Lys at position 240. In addition to the production of this novel ESBL, designated SHV-18, analysis of the outer membrane proteins of K6 revealed the loss of the OmpK35 and OmpK37 porins.

Rapid discriminatory detection of genes coding for SHV beta-lactamases by ligase chain reaction

Ligase chain reaction (LCR) is a recently developed technique that employs a thermostable ligase and allows for the discrimination of DNA sequences differing in only a single base pair. The method has been adapted and applied to differentiation of bla(SHV) genes. We have developed an LCR typing method to characterize point mutations in genes for SHV-derived extended-spectrum beta-lactamases with four different sets of biotinylated LCR primers. To evaluate the applicability of the current technique, we tested seven Escherichia coli strains producing SHV-1, SHV-2, SHV-2a, SHV-3, SHV-4, SHV-5, and SHV-12. With the LCR typing, seven SHV genes can be distinguished according to their incorporating point mutations. In an attempt to characterize SHV beta-lactamases by LCR typing in clinical isolates, 46 strains carrying bla(SHV) genes (32 Klebsiella pneumoniae, 10 Enterobacter cloacae, and 4 E. coli) were subjected to antibiotic susceptibility testing, isoelectric focusing, and LCR typing. LCR typing allowed the characterization of beta-lactamases, and genotypes obtained by LCR typing were in accordance with phenotypes such as antibiotic resistance profile and pI value of beta-lactamase. Therefore, we concluded that LCR typing may permit defining the SHV families with simplicity and reliability and can be applied to the detailed characterization and molecular epidemiology of SHV-type beta-lactamases.

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

Twenty (8.5%) of 234 nonrepetitive clinical isolates of Klebsiella pneumoniae from southern Taiwan were found to produce extended-spectrum beta-lactamases (ESBLs): 10 strains produced SHV-12, 4 produced SHV-5, 2 produced a non-TEM non-SHV ESBL with a pI of 8.3, 3 produced a novel AmpC beta-lactamase designated CMY-8 with a pI of 8.25, and 1 produced SHV-12 and an unidentified AmpC enzyme with a pI of 8.2. The CMY-8 enzyme confers a resistance phenotype similar to CMY-1 and MOX-1, and sequence comparisons showed high homologies (>95%) of nucleotide and amino acid sequences among these three enzymes. Plasmid and pulse-field gel electrophoresis analyses revealed that all isolates harboring an SHV-derived ESBL were genetically unrelated, indicating that dissemination of resistance plasmids is responsible for the spread of SHV ESBLs among K. pneumoniae in this area. All three isolates carrying CMY-8 had identical genotypic patterns, suggesting the presence of an epidemic strain.