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

Extended Spectrum Beta-Lactamase (ESBL) Produced by Gram-Negative Bacteria in Trinidad and Tobago

Gram-negative bacterial infections are a global health problem. The production of beta-lactamase is still the most vital factor leading to beta-lactam resistance. In Trinidad and Tobago, extended spectrum beta-lactamase (ESBL) production has been detected and reported mainly in the isolates of Klebsiella pneumoniae and Escherichia coli and constitutes a public health emergency that causes high morbidity and mortality in some patients. In this literature review, the authors cover vast information on ESBL frequency and laboratory detection using both conventional and molecular methods from clinical data. The aim is to make the reader reflect on how the actual knowledge can be used for rapid detection and understanding of the spread of antimicrobial resistance problems stemming from ESBL production among common Gram-negative organisms in the health care system.

A Review of SHV Extended-Spectrum β-Lactamases: Neglected Yet Ubiquitous

β-lactamases are the primary cause of resistance to β-lactams among members of the family Enterobacteriaceae. SHV enzymes have emerged in Enterobacteriaceae causing infections in health care in the last decades of the Twentieth century, and they are now observed in isolates in different epidemiological settings both in human, animal and the environment. Likely originated from a chromosomal penicillinase of Klebsiella pneumoniae, SHV β-lactamases currently encompass a large number of allelic variants including extended-spectrum β-lactamases (ESBL), non-ESBL and several not classified variants. SHV enzymes have evolved from a narrow- to an extended-spectrum of hydrolyzing activity, including monobactams and carbapenems, as a result of amino acid changes that altered the configuration around the active site of the β -lactamases. SHV-ESBLs are usually encoded by self-transmissible plasmids that frequently carry resistance genes to other drug classes and have become widespread throughout the world in several Enterobacteriaceae, emphasizing their clinical significance.

Molecular characterization and in vitro susceptibilities of β-lactamase producing Escherichia coli, Klebsiella species, Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus to CSE1034 and other β-lactams

OBJECTIVE

To study the prevalence of extended-spectrum β-lactamases (ESBLs) among 663 clinical isolates obtained from various parts of India and to study the occurrence of different variants of ESBLs among these isolates.

METHODS

Phenotypic characterization and susceptibility studies were performed according to the methods described in Clinical and Laboratory Standards Institute guidelines. The occurrence of ESBL variants was analyzed with PCR using the previously reported primers.

RESULTS

Among the six hundred sixty three isolates, the identified isolates were Acinetobacter baumannii (72), Escherichia coli (218), Klebsiella pneumoniae (30), Klebsiella oxytoca (63), Pseudomonas aeruginosa (264) and Staphylococcus aureus (16). PCR results revealed that approximately 89.0% of Pseudomonas aeruginosa isolates were positive for ESBL followed by Escherichia coli (85.3%), Klebsiella pneumoniae (76.6%), Klebsiella oxytoca (73.0%), Acinetobacter baumannii (72.2%) and Staphylococcus aureus (31.2%). The overall prevalence of ESBL was 82.5%. The presence of TEM type ESBLs were the predominant (in 186 isolates), followed by SHV (138), OXA (92), CTX-M (65), AmpC (33), KPC (28) and blaZ (5). Of the drugs involved in the study, CSE1034 was found to be the most efficacious against all of ESBL positive clinical isolates showing susceptibility approximately 95.7% with minimal inhibitory concentration values between 0.125 and 8.000 μg/mL for all strains tested. The susceptibilities of penems (meropenem and imipenem and cilastatin) ranged between 83% and 93% for all the isolates. The susceptibilities of other drugs like piperacillin and tazobactam, amoxicillin and clavulanic acid, cefoperazone and sulbactam were <45% for all the isolates.

CONCLUSIONS

Results of the present study indicated that majority of the isolates was susceptible to CSE1034 and it could be a potent antibacterial agent for the treatment of severe bacterial infections caused by such organisms.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae: an emerging public-health concern

The medical community relies on clinical expertise and published guidelines to assist physicians with choices in empirical therapy for system-based infectious syndromes, such as community-acquired pneumonia and urinary-tract infections (UTIs). From the late 1990s, multidrug-resistant Enterobacteriaceae (mostly Escherichia coli) that produce extended-spectrum beta lactamases (ESBLs), such as the CTX-M enzymes, have emerged within the community setting as an important cause of UTIs. Recent reports have also described ESBL-producing E coli as a cause of bloodstream infections associated with these community-onset UTIs. The carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by ESBL-producing Enterobacteriaceae, although comparative clinical trials are scarce. Thus, more rapid diagnostic testing of ESBL-producing bacteria and the possible modification of guidelines for community-onset bacteraemia associated with UTIs are required.

Molecular analysis of the simultaneous production of two SHV-type extended-spectrum beta-lactamases in a clinical isolate of Enterobacter cloacae by using single-nucleotide polymorphism genotyping

Bacteria that simultaneously produce multiple extended-spectrum beta-lactamases are frequently isolated. We report an Enterobacter cloacae isolate, ES24, producing four different beta-lactamases (AmpC type beta-lactamase, TEM-1, SHV-7, and a novel extended-spectrum beta-lactamase, SHV-30). Direct sequencing of bla(SHV) gene products gave a "double peak" at position 703, suggesting the presence of more than one allele. Using fluorescence resonance energy transfer real-time PCR to detect single-nucleotide polymorphisms, we were able to distinguish two different bla(SHV) genes in a single isolate. This may prove to be a useful technique in surveys of beta-lactamase production in contemporary clinical isolates.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Predominance and genetic diversity of community- and hospital-acquired CTX-M extended-spectrum β-lactamases in York, UK

OBJECTIVES

This study was conducted to detect the presence of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae within the faecal flora of both community- and hospital-based patients in York and to characterize the bla(TEM), bla(SHV) and bla(CTX-M) genes present in these isolates.

METHODS

One thousand faeces samples were collected and screened at York Hospital during October-December 2003. Ninety-five non-duplicate Enterobacteriaceae isolates resistant to third-generation cephalosporins were recovered; 22 isolates were selected for further study on the basis of a positive double disc diffusion test for ESBL production. Antibiotic susceptibility testing was performed to a range of antibiotics. The TEM, SHV and CTX-M genes were detected by PCR and the DNA sequenced.

RESULTS

The distribution of ESBL-positive isolates from the hospital and community was 1.4:1. These included nine Escherichia coli, seven Enterobacter cloacae, four Citrobacter freundii and a single isolate each of Klebsiella spp. and Salmonella spp. A total of 17 isolates contained bla(CTX-M) (five bla(CTX-M-15), three bla(CTX-M-14) and nine bla(CTX-M-9)). ISEcp1 was present in isolates expressing CTX-M-14 and -15, but was absent upstream of In60-associated bla(CTX-M-9). E. coli isolates also contained either a bla(TEM-1) or bla(TEM-2), whereas six of the E. cloacae carried bla(SHV-12) and the Klebsiella spp. bla(SHV-36) in addition to bla(CTX-M-9). The single Salmonella spp. carried bla(SHV-12).

CONCLUSIONS

The overall prevalence of ESBL in isolates of Enterobacteriaceae from York was 1.9%. ESBL-producing isolates were found in both the community and hospital, with the CTX-M type most common. This is also the first report of an ESBL-producing Salmonella in the UK.

Antibiotic resistance in the institutionalized elderly

Geriatric patients frequently are cared for in long term care facilities (LTCFs), which are now a major component of our health care delivery system. Nearly half of the 2.2 million people who turned 65 years old in 1990 will enter an LTCF at least once before they die. Infections are one of the principal causes of morbidity and mortality in LTCFs. Because LTCFs are a less costly alternative to hospitalization, clinicians are treating many serious infections in the nursing home. As a result of antibiotic use, LTCFs will increasingly be recognized as sources of organisms resistant to multiple antibiotics. b-Lactams are a valuable class of potent antimicrobials with broad-spectrum activity against Gram-negative and Gram-positive organisms. The safety and efficacy of this class of antibiotics make them easy choices for empiric treatment of infections in the elderly. Unfortunately, excessive use of these antibiotics has created serious threats to our therapeutic armamentarium: the emergence of methicillin-resistant Staphylococcus aureus and of Gram-negative pathogens resistant to third-generation cephalosporins such as cefotaxime, ceftazidime, and ceftriaxone. Of these third-generation cephalosporins, resistance to ceftazidime is most frequently recognized. The major mechanism responsible for ceftazidime resistance in Gram-negative bacteria is the production of b-lactamases. This article summarizes the diversity of b-lactamases, highlights the important enzymes that confer ceftazidime resistance in LTCFs, and details some methods used to identify and characterize these enzymes. A clear challenge is to apply these techniques to epidemiologic and molecular studies conducted in LTCFs.

Extended-spectrum beta-lactamases: the European experience

Extended-spectrum beta-lactamases mediate resistance to cephalosporin antibiotics and were first discovered in Europe in the early 1980s. They have become a widespread problem, particularly in Klebsiella pneumoniae, but increasingly in non-typhoid Salmonella species. Traditionally, extended-spectrum beta-lactamases have been derivatives of TEM and SHV parent enzymes. The last year, however, has seen an explosion of developments in extended-spectrum beta-lactamases of non-TEM, non-SHV lineage in Europe. The CTX-M type extended-spectrum beta-lactamases have become particularly widespread. At the same time, European clinical microbiology laboratories have become more aware of the pressing need for detection methods given increasing awareness of the lack of reliability of cephalosporins in the treatment of extended-spectrum beta-lactamase producers.