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.     

Extended-spectrum beta-lactamases (ESbLs): characterization, epidemiology and detection

Beta-lactamases of Enterobacteriaceae are the most important mechanism of resistance against beta-lactam drugs. Two types of beta-lactamases can confer resistance against 3rd generation cephalosporins. Chromosomally mediated beta-lactamases are inducible and are not inhibited by clavulanic acid. Resistance due to these enzymes is non-transferable. The 2nd type of enzyme is plasmid-mediated beta-lactamases, which are inhibited by clavulanic acid. These enzymes are more important clinically as these can be transferred between various species of Enterobacteriaceae. These enzymes are called extended-spectrum beta-lactamases (ESBLs). ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Antibacterial choice is often complicated by multi-resistance. ESBLs can confer resistance against all beta-lactam drugs except carbapenems and cephamycins. Nursing home patients may be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms. Use of broad-spectrum oral antibiotics and probably poor infection control practices may facilitate spread of this plasmid-mediated resistance. In addition to known populations at risk, ambulatory patients with chronic conditions represent another patient population that may harbor ESBL-producing organisms. Various methods can be used for detection of ESBLs in the laboratory. These tests include double disc diffusion test, Vitek ESBL test, E Tests, MIC Determination, genetic method, and isoelectric focusing (IEF).     

Extended-spectrum beta-lactamases in the 21st century: characterization, epidemiology, and detection of this important resistance threat

Beta-lactamases continue to be the leading cause of resistance to beta-lactam antibiotics among gram-negative bacteria. In recent years there has been an increased incidence and prevalence of extended-spectrum beta-lactamases (ESBLs), enzymes that hydrolyze and cause resistance to oxyimino-cephalosporins and aztreonam. The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel, unrelated beta-lactamases. Several different methods for the detection of ESBLs in clinical isolates have been suggested. While each of the tests has merit, none of the tests is able to detect all of the ESBLs encountered. ESBLs have become widespread throughout the world and are now found in a significant percentage of Escherichia coli and Klebsiella pneumoniae strains in certain countries. They have also been found in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Strains expressing these beta-lactamases will present a host of therapeutic challenges as we head into the 21st century.     

The characteristics of extended-spectrum beta-lactamases in Korean isolates of Enterobacteriaceae

Extended-spectrum beta-lactamases (ESBLs) in gram-negative organisms have been implicated as the enzymes responsible for resistance to oxyimino-cephalosporins. The incidence of ESBL-producers in Korean isolates of Escherichia coli and Klebsiella pneumoniae were in the range of 4.8-7.5% and 22.5-22.8%, respectively. The ESBL-producing isolates revealed variable levels of resistance to cefotaxime, ceftazidime and aztreonam. They also showed the elevated MIC values of non-beta-lactam antibiotics. SHV-12 and SHV-2a were the enzymes most frequently found in K. pneumoniae strains, but TEM-52 was the most prevalent in E. coli isolates. About 15% of ESBL-producing isolates of Enterobacteriaceae produced CMY-1 enzyme, which conferred resistance to cephamycins such as cefoxitin as well as oxyimino-cephalosporins. Thus, the most common types of ESBLs in Korea are TEM-52, SHV-12 SHV-2a, and CMY-1.     

Mechanistic and clinical aspects of beta-lactam antibiotics and beta-lactamases.

Bacterial infections have been a major cause of concern in the recent years due to the emergence of drug resistance strains and inability of the current therapeutic regimens to treat these infections in certain cases. Beta-Lactam antibiotics have been drugs of choice since the introduction of penicillin. These drugs inhibit bacterial cell-wall-synthesizing enzymes, the so-called penicillin-binding proteins (PBPs) selectively, thus providing an effective strategy for treatment of the bacterial infections. Significantly, bacteria have developed resistance mechanisms to neutralize the antibiotic action of beta-lactam drugs. Beta-Lactamases are enzymes that hydrolyze the beta-lactam moiety of these drugs, rendering them inactive. This is the primary mechanism of resistance to this class of antibiotics. There are 255 known beta-lactamases to date and the continued use of beta-lactams may select for newer variants yet. A discussion of the roles of these enzymes in the manifestation of the drug-resistant phenotype and their implications for pathogenecity of clinical strains of bacteria is presented.     

Detection and reporting of organisms producing extended-spectrum beta-lactamases: survey of laboratories in Connecticut

Extended-spectrum beta-lactamases (ESBLs) are enzymes produced in some gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. They are most common in Klebsiella spp. and Escherichia coli but are present in a variety of Enterobacteriaceae. Resistance mediated by these enzymes can be difficult to detect depending on the antimicrobial agents tested. AmpC beta-lactamases are related to the chromosomal enzymes of Enterobacter and Citrobacter spp. and also mediate resistance to extended-spectrum cephalosporins and aztreonam in addition to cephamycins, such as cefoxitin. Unlike ESBLs, however, AmpC beta-lactamases are not inhibited by clavulanic acid or other similar compounds. To assess the abilities of various antimicrobial susceptibility testing methods to detect ESBLs, we sent three ESBL-producing organisms, one AmpC-producing organism, and a control strain that was susceptible to extended-spectrum cephalosporins to 38 laboratories in Connecticut for testing. Eight (21.0%) of 38 labs failed to detect extended-spectrum cephalosporin or aztreonam resistance in any of the ESBL- or AmpC-producing isolates. Errors were encountered with both automated and disk diffusion methods. Conversely, seven (18.4%) labs categorized at least some of the four resistant isolates as potential ESBL producers and reported the results with the extended-spectrum cephalosporins and aztreonam as resistant as suggested by current National Committee for Clinical Laboratory Standards (NCCLS) guidelines. The percentage of laboratories that failed to detect resistance in the ESBL or AmpC isolates ranged from 23.7 to 31.6% depending on the type of enzyme present in the test organism. This survey suggests that many laboratories have difficulty detecting resistance in ESBL and AmpC-producing organisms and may be unaware of the NCCLS guidelines on modifying susceptibility testing reports for ESBL-producing strains.     

Concentration-dependency of beta-lactam-induced filament formation in Gram-negative bacteria.

Ceftazidime and cefotaxime are beta-lactam antibiotics with dose-related affinities for penicillin-binding protein (PBP)-3 and PBP-1. At low concentrations, these antibiotics inhibit PBP-3, leading to filament formation. Filaments are long strands of non-dividing bacteria that contain enhanced quantities of endotoxin molecules. Higher concentrations of ceftazidime or cefotaxime cause inhibition of PBP-1, resulting in rapid bacterial lysis, which is associated with low endotoxin release. In the present study, 37 isolates of Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa and Acinetobacter spp. were studied over a 4-h incubation period in the presence of eight concentrations of ceftazidime or cefotaxime. As resistance of Gram-negative bacteria is an emerging problem in clinical practice, 14 isolates of E. coli and Klebsiella pneumoniae that produced extended-spectrum beta-lactamases (ESBLs) were also investigated. Morphological changes after exposure to the beta-lactam antibiotics revealed recognisable patterns in various bacterial families, genera and isolates. In general, all isolates of Enterobacteriaceae produced filaments within a relatively small concentration range, with similar patterns for E. coli and K. pneumoniae. Pseudomonas and Acinetobacter spp. produced filaments in the presence of clinically-relevant concentrations of both antibiotics as high as 50 mg/L. In all genera, filament-producing capacity was clearly related to the MIC. Ceftazidime induced filament production in more isolates and over wider concentration ranges than did cefotaxime. Interestingly, ESBL-producing isolates were not protected against filament induction. The induction of filament production may lead to additional risks during empirical treatment of severe infections.     

Clinical significance of extended-spectrum beta-lactamases

Extended-spectrum beta-lactamases (ESBLs) have now been described in many hospitals worldwide. While they have been detected in many pathogenic gram-negative bacteria, they are particularly prevalent inKlebsiella isolates. Known risk factors for colonization and/or infection with organisms harboring these enzymes include admission to an intensive care unit, recent surgery, instrumentation, prolonged hospital stay and antibiotic exposure, especially exposure to extended-spectrum beta-lactam agents. In this report three recent epidemics from the USA will be described in which the role of selective antibiotic pressure seems clear. Data from two hospital epidemics, one from New York and another from Stanford, California, will be reviewed briefly. In addition, recent studies describing the spread of extended-spectrum beta-lactamases among nursing home patients in Chicago, Illinois, will be outlined. The limited data available on treatment options for patients infected with ESBL-containing strains will be reviewed, focusing on the activity of piperacillin/tazobactam and imipenem against these otherwise broadly resistant strains. Lastly, attempts to control these organisms, including infection control measures and selective bowel decontamination, will be reviewed.     

Emergence of resistance in gram-negative bacteria during therapy with expanded-spectrum cephalosporins

To assess the clinical importance of emergence of beta-lactam resistance caused by stable derepression of chromosomal beta-lactamases, sequential cultures from patients treated with expanded-spectrum cephalosporins were monitored for the persistence of bacteria possessing these enzymes. Antibiotic susceptibilities and beta-lactamase production before and after cefoxitin induction were determined in sequential isolates of individual bacterial strains. Of 49 strains isolated from 44 patients, 25 strains (51%) were eradicated by cephalosporin therapy, 17 strains (35%) persisted with unchanged susceptibility in sequential cultures, and 7 strains (14%) from 7 patients developed multiple beta-lactam resistance during cephalosporin therapy. In 6 of the 7 strains, resistance was associated with stable derepression of beta-lactamases. In the patient group whose strains developed resistance, subsequent use of non-beta-lactam antibiotics was more frequent and mortality was higher.     

Mechanisms of resistance in Enterobacteriaceae towards beta-lactamase antibiotics

Except for Salmonella spp., all Enterobacteriaceae produce intrinsic chromosomal encoded beta-lactamases which, beside their physiologic role in cell-wall synthesis and natural beta-lactam protection, are responsible for intrinsic resistance of individual species among Enterobacteriaceae. E. coli and Shigella spp. produce a small amount of AmpC beta-lactamases and are susceptible to ampicillin and other beta-lactam antibiotic agents. Enterobacter spp, C. freundii, Serratia spp., M. morganii, P. stuarti and P. rettgeri produce small amounts of inducible AmpC beta-lactamases which are not inhibited by beta-lactamases inhibitor, causing intrinsic resistance to ampicillin, co-amoxiclav and first-generation cephalosporins. K. pneumoniae produces small amounts of SHV-1 beta-lactamases, and K. oxytoca chromosomal K1 beta-lactamase, causing resistance to ampicillin, carbencillin, ticarcillin and attenuated zone of inhibition to piperacillin, compared to piperacillin with tazobactam. They are susceptible to beta-lactamase inhibitors. Whereas P. mirabilis shows a minor chromosomal expression of beta-lactamases, P. vulgaris produces chromosomal beta-lactamases of class A (cefuroximases), causing resistance to ampicillin, ticarcillin, and first- and second-generation cephalosporins. Antibiotics have caused the appearance of acquired or secondary beta-lactamases, with the sole function of protecting bacteria from antibiotics. The production of broad-spectrum beta-lactamases (TEM-1, TEM-2, SHV-1, OXA-1) results in resistance to ampicillin, ticarcillin, first-generation cephalosporins and piperacillin. A high level of beta-lactamases leads to resistance to their inhibitors. The plasmid-mediated extended-spectrum beta-lactamases (ESBLs) are of increasing concern. Most are mutants of classic TEM- and SHV-beta-lactamases types. Unlike these parent enzymes, ESBLs hydrolyze oxymino-cephalosporins such as cefuroxime, cefotaxime, ceftriaxone, ceftizoxime, ceftazidime, cefpirome and cefepime, aztreonam, as well as penicillins and other cephalosporins, except for cephamycin (cefoxitin and cefotetan). They are inhibited by beta-lactamase inhibitors. AmpC beta-lactamases are chromosomal and inducible in most Enterobacter spp., C. freundii, Serratia spp., M. morganii and Providentia spp. They are resistant to almost all penicillins and cephalosporins, to beta-lactamase inhibitors and aztreonam, and are susceptible to cefepime and carbapenems as well. Plasmid-mediated AmpC beta-lactamases have arisen through the transfer of chromosomal genes for the inducible AmpC beta-lactamase onto plasmids. All plasmid-mediated AmpC beta-lactamases have similar substrate profiles to the parental enzymes from which they appear to be derived. With one exception, plasmid-mediated AmpCs differ from chromosomal AmpCs in being uninducible. The National Committee for Clinical Laboratory Standards (NCCLS) has issued recommendations for ESBL screening and confirmation for isolates of E. coli, K. pneumoniae and K. oxytoca. No NCCLS recommendations exist for ESBLs detection and reporting for other organisms or for detecting plasmid-mediated AmpC beta-lactamases. High-level expression of AmpC may prevent recognition of an ESBL in species that produce a chromosomally encoded inducible AmpC beta-lactamase. AmpC-inducible species (e. g. Enterobacter spp. and C. freundii) can be recognized by cefoxitin/cefotaxime disk antagonism tests. Since clinical laboratories are first to encounter bacteria with new forms of antibiotic resistance, they need appropriate tools to recognize these bacteria, including trained staff with sufficient time and equipment to follow up important observations. Because bacterial pathogenes are constantly changing, training must be an ongoing process.     

Outcome of cephalosporin treatment for serious infections due to apparently susceptible organisms producing extended-spectrum beta-lactamases: implications for the clinical microbiology laboratory

Although extended-spectrum beta-lactamases (ESBLs) hydrolyze cephalosporin antibiotics, some ESBL-producing organisms are not resistant to all cephalosporins when tested in vitro. Some authors have suggested that screening klebsiellae or Escherichia coli for ESBL production is not clinically necessary, and when most recently surveyed the majority of American clinical microbiology laboratories did not make efforts to detect ESBLs. We performed a prospective, multinational study of Klebsiella pneumoniae bacteremia and identified 10 patients who were treated for ESBL-producing K. pneumoniae bacteremia with cephalosporins and whose infecting organisms were not resistant in vitro to the utilized cephalosporin. In addition, we reviewed 26 similar cases of severe infections which had previously been reported. Of these 36 patients, 4 had to be excluded from analysis. Of the remaining 32 patients, 100% (4 of 4) patients experienced clinical failure when MICs of the cephalosporin used for treatment were in the intermediate range and 54% (15 of 28) experienced failure when MICs of the cephalosporin used for treatment were in the susceptible range. Thus, it is clinically important to detect ESBL production by klebsiellae or E. coli even when cephalosporin MICs are in the susceptible range (相似文献   

Cefuroxime stability to beta-lactamases: clinical implications

Bacteria continuously evolve their resistance mechanisms to antibiotics, either in community or in the hospital setting. Production of beta-lactamases is one of the oldest way to overcome antimicrobial agents activity, since it was first described in 1944 immediately after the penicillin discovery. Beta-lactamases are enzymes hydrolysing the beta-lactam nucleus of beta-lactam antibiotics by using two strategies: a nucleophilic attack of a serine residue or activating a water molecule via a Zn++. Cefuroxime is a injectable cephalosporin which can be also orally administered as a pro-drug named cefuroxime axetil. Cefuroxime has been classified as a second generation cephalosporin, even though the strict subgrouping of cephalosporins into classes is critically discussed by the Authors. Cefuroxime was the first beta-lactam with a higher stability to beta-lactamase hydrolysis due to its methoxy-imino side chain in position 7 of the cephem nucleus. Many of the clinically significant bacterial species producing beta-lactamases such as Haemophilus, Moraxella, Staphylococci and most Enterobacteriaceae then remain susceptible to cefuroxime. The more evoluted enzymes such as carbapenemases, extended-spectrum beta-lactamases or over-expressed cephalosporinases hydrolyse nearly all the beta-lactams antibiotics including cefuroxime. The available literature on the bacterial susceptibility to cefuroxime in Italy and use of cefuroxime in clinical settings where beta-lactamase producing bacteria could be involved has been analysed in the review. In conclusion, cefuroxime still represents a valid therapeutic option even in presence of most of the beta-lactamase producing bacteria.     

Extended-Spectrum β-Lactamases (ESBLs): Characterization,Epidemiology and Detection

β-lactamases of Enterobacteriaceae are the most important mechanism of resistance against β-lactam drugs. Two types of β-lactamases can confer resistance against 3rd generation cephalosporins. Chromosomally mediated β-lactamases are inducible and are not inhibited by clavulanic acid. Resistance due to these enzymes is non-transferable. The 2nd type of enzyme is plasmid-mediated β-lactamases, which are inhibited by clavulanic acid. These enzymes are more important clinically as these can be transferred between various species of Enterobacteria ceae. These enzymes are called extended-spectrum β-lactamases (ESBLs). ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world and pose challenging infection control issues. Antibacterial choice is often complicated by multi-resistance. ESBLs can confer resistance against all β-lactam drugs except carbapenems and cephamycins. Nursing home patients may be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms. Use of broad-spectrum oral antibiotics and probably poor infection control practices may facilitate spread of this plasmid-mediated resistance. In addition to known populations at risk, ambulatory patients with chronic conditions represent another patient population that may harbor ESBL-producing organisms. Various methods can be used for detection of ESBLs in the laboratory. These tests include double disc diffusion test, Vitek ESBL test, E Tests, MIC Determination, genetic method, and isoelectric focusing (IEF).     

Evolution and epidemiology of extended-spectrum β-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 β -lactamases with wide spectra of substrate specificity illustrates very well all the phenomena mentioned above. Being able to hydrolyze the majority of β -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 β -lactamases (ESBLs) and different types of β -lactamases with carbapenemase activity, of which the so-called class B metallo- β -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.     

Clinical importance of inducible beta-lactamases in gram-negative bacteria

The clinical problems caused by inducible beta-lactamases in certain gram-negative bacteria are being recognized with increasing frequency. These problems include the rapid emergence of multiple beta-lactam resistance during therapy with many of the newer beta-lactam antibiotics. Such multiply resistant organisms are now spreading within the hospital and have become important nosocomial pathogens. This has been a particularly difficult problem for intensive care units, cystic fibrosis centers and burn units where there are clusters of patients who are highly susceptible to infections with organisms likeEnterobacter spp.,Serratia spp. andPseudomonas aeruginosa, which possess inducible beta-lactamases. Only through an awareness of these problems, their cause, and restriction of the use of certain newer betalactam antibiotics can these problems be controlled.     

Beta-lactamase inhibitors from laboratory to clinic.

beta-Lactamases constitute the major defense mechanism of pathogenic bacteria against beta-lactam antibiotics. When the beta-lactam ring of this antibiotic class is hydrolyzed, antimicrobial activity is destroyed. Although beta-lactamases have been identified with clinical failures for over 40 years, enzymes with various abilities to hydrolyze specific penicillins or cephalosporins are appearing more frequently in clinical isolates. One approach to counteracting this resistance mechanism has been through the development of beta-lactamase inactivators. beta-Lactamase inhibitors include clavulanic acid and sulbactam, molecules with minimal antibiotic activity. However, when combined with safe and efficacious penicillins or cephalosporins, these inhibitors can serve to protect the familiar beta-lactam antibiotics from hydrolysis by penicillinases or broad-spectrum beta-lactamases. Both of these molecules eventually inactivate the target enzymes permanently. Although clavulanic acid exhibits more potent inhibitory activity than sulbactam, especially against the TEM-type broad-spectrum beta-lactamases, the spectrum of inhibitory activities are very similar. Neither of these inhibitors acts as a good inhibitor of the cephalosporinases. Clavulanic acid has been most frequently combined with amoxicillin in the orally active Augmentin and with ticarcillin in the parenteral beta-lactam combination Timentin. Sulbactam has been used primarily to protect ampicillin from enzymatic hydrolysis. Sulbactam has been used either in the orally absorbed prodrug form as sultamicillin or as the injectable combination ampicillin-sulbactam. Synergy has been demonstrated for these combinations for most members of the Enterobacteriaceae, although those organisms that produce cephalosporinases are not well inhibited. Synergy has also been observed for Neisseria gonorrhoeae, Haemophilus influenzae, penicillinase-producing Staphylococcus aureus, and anaerobic organisms. These antibiotic combinations have been used clinically to treat urinary tract infections, bone and soft-tissue infections, gonorrhea, respiratory infections, and otitis media. Gastrointestinal side effects have been reported for Augmentin and sultamicillin; most side effects with these agents have been mild. Although combination therapy with beta-lactamase inactivators has been used successfully, the problem of resistance development to two agents must be considered. Induction of cephalosporinases can occur with clavulanic acid. Permeability mutants could arise, especially with added pressure from a second beta-lactam.(ABSTRACT TRUNCATED AT 250 WORDS)     

Extended-spectrum beta-lactamase-producing Klebsiella spp

Extended-spectrum beta-lactamases (ESBLs) are associated particularly with Klebsiella spp. These enzymes have arisen by mutation of the genes coding for clavulanate-sensitive, plasmid-mediated beta-lactamases such as TEM-1, TEM-2 and SHV-1. Amino acid changes in ESBLs confer enhanced hydrolysis of oxyimino-aminothiazolyl beta-lactams and aztreonam. Enzyme hyperproduction and loss of porins contribute to hydrolytic efficiency. ESBLs are highly susceptible to inhibition by clavulanate, and their presence can be detected by the disc-approximation test, using amoxycillin/clavulanate and an ESBL-susceptible antibiotic. Other manual procedures have been used and commercial tests to detect the enzymes include Etest, Vitek and Dade Microscan products. The epidemiology of ESBLs is complex, and epidemic and sporadic strains may be encountered in the same hospital. Spread between hospitals--even countries--has been documented. ESBL activity is carried on large plasmids that often carry determinants for resistance to aminoglycosides and other antibiotics, and this is transmissible to Escherichia coli and other species of Enterobacteriaceae in which ESBLs have been detected.     

Extended-spectrum beta-lactamases in Taiwan: epidemiology, detection, treatment and infection control.

Extended-spectrum beta-lactamases (ESBLs) efficiently hydrolyze extended-spectrum beta-lactams such as cefotaxime, ceftriaxone, ceftazidime, and aztreonam. ESBLs are most often plasmid-mediated. In Taiwan, the prevalence of ESBLs in bacteria has risen, ranging from 8.5 to 29.8% in Klebsiella pneumoniae and 1.5 to 16.7% in Escherichia coli isolates. The most prevalent types of ESBLs are SHV-5, SHV-12, CTX-M-3, and CTX-M-14 in isolates of K. pneumoniae and E. coli, with differences between institutions. SHV-12 and CTX-M-3 have been reported as the most common ESBLs in isolates of Enterobacter cloacae and Serratia marcescens, respectively. Molecular epidemiology studies suggest that the ESBL-encoding genes have been disseminated either by proliferation of epidemic strains or by transfer of plasmids carrying the resistance traits. The current ESBL screen guidelines of the Clinical and Laboratory Standards Institute (formerly National Committee for Clinical Laboratory Standards) are issued for E. coli, Klebsiella spp., and Proteus mirabilis. Owing to the lack of standard methods, it remains difficult to assure the presence of ESBL in an isolate co-harboring an AmpC beta-lactamase, particularly in cases where the latter is produced in larger amounts than the former. Empirical therapy with piperacillin-tazobactam to replace third-generation cephalosporins may help to reduce the occurrence of ESBLs in an institution with a high prevalence of ESBL producers. Carbapenems remain the drugs of choice for serious infections caused by ESBL-producing organisms. To retard the selection for carbapenem-resistant bacteria, 7-alpha-methoxy beta-lactams or fourth-generation cephalosporins can be therapeutic alternatives for mild-to-moderate infections provided that the pharmacokinetic and pharmacodynamic target can be easily achieved.     

Characterization of clinical isolates of Enterobacteriaceae from Italy by the BD Phoenix extended-spectrum beta-lactamase detection method

Production of extended-spectrum beta-lactamases (ESBLs) is an important mechanism of beta-lactam resistance in Enterobacteriaceae: Identification of ESBLs based on phenotypic tests is the strategy most commonly used in clinical microbiology laboratories. The Phoenix ESBL test (BD Diagnostic Systems, Sparks, Md.) is a recently developed automated system for detection of ESBL-producing gram-negative bacteria. An algorithm based on phenotypic responses to a panel of cephalosporins (ceftazidime plus clavulanic acid, ceftazidime, cefotaxime plus clavulanic acid, cefpodoxime, and ceftriaxone plus clavulanic acid) was used to test 510 clinical isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, Providencia stuartii, Morganella morganii, Enterobacter aerogenes, Enterobacter cloacae, Serratia marcescens, Citrobacter freundii, and Citrobacter koseri. Of these isolates, 319 were identified as ESBL producers, and the remaining 191 were identified as non-ESBL producers based on the results of current phenotypic tests. Combined use of isoelectric focusing, PCR, and/or DNA sequencing demonstrated that 288 isolates possessed bla(TEM-1)- and/or bla(SHV-1)-derived genes, and 28 had a bla(CTX-M) gene. Among the 191 non-ESBL-producing isolates, 77 isolates produced an AmpC-type enzyme, 110 isolates possessed TEM-1, TEM-2, or SHV-1 beta-lactamases, and the remaining four isolates (all K. oxytoca strains) hyperproduced K1 chromosomal beta-lactamase. The Phoenix ESBL test system gave positive results for all the 319 ESBL-producing isolates and also for two of the four K1-hyperproducing isolates of K. oxytoca. Compared with the phenotypic tests and molecular analyses, the Phoenix system displayed 100% sensitivity and 98.9% specificity. These findings suggest that the Phoenix ESBL test can be a rapid and reliable method for laboratory detection of ESBL resistance in gram-negative bacteria.     

Bactericidal activity of three β-lactams alone or in combination with a β-lactamase inhibitor and two aminoglycosides against Klebsiella pneumoniae harboring extended-spectrum β-lactamases

Objective: To study the bactericidal activity of β-lactam antibiotics (imipenem, cefepime, cefpirome) alone or in combination with a β-lactamase inhibitor (sulbactam) in the presence or absence of aminoglycoside (amikacin or isepamicin) against Klebsiella pneumoniae strains producing extended-spectrum β-lactamases (ESBLs).
Methods: We characterized 10 strains by means of analytic isoelectric focusing and pulsed-field gel electrophoresis. The ESBLs produced by these strains were derived from either TEM (TEM-1, TEM-2) or SHV-1. The killing-curve method was used for this bacterial investigation. Bacteria (final inoculum 5×10 ⁵ CFU/mL) were incubated with antibiotics at clinical concentrations obtained in vivo.
Results: All the combinations with cefepime or cefpirome + sulbactam were bactericidal, with a 4 log₁₀ decrease being obtained within 6 h without regrowth at 24 h, whereas imipenem alone, and combinations, gave a bactericidal effect within 6 h. The two cephalosporins alone decreased the inoculum of 4 log₁₀ at 6 h but regrowth was observed at 24 h. When the aminoglycoside was added, this bactericidal effect was obtained within 3 h with amikacin and within 1 h with isepamicin.
Conclusions: Cefepime + sulbactam or cefpirome + sulbactarn may be an alternative to imipenem for the treatment of patients with ESBL-producing K. pneumoniae. Aminoglycosides are often associated in nosocomial infections due to ESBL-producing K. pneumoniae: isepamicin acted faster than amikacin, but both worked well. To conclude, it may be prudent to avoid extended-spectrum cephalosporins as single agent when treating serious infections due to ESBL-producing K. pneumoniae. Addition of a β-lactamase inhibitor such as sulbactam ± aminoglycoside is advisable to avoid failure of treatment.