Aztreonam

About: Aztreonam is a research topic. Over the lifetime, 1990 publications have been published within this topic receiving 54459 citations. The topic is also known as: SO-26776 & SQ-26776.

Extended-spectrum beta-lactamases: a clinical update.

Abstract: Extended-spectrum β-lactamases (ESBLs) are a rapidly evolving group of β-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 β-lactamases. This extends the spectrum of β-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 Broad-Spectrum β-Lactamases Conferring Transferable Resistance to Newer β-Lactam Agents in Enterobacteriaceae: Hospital Prevalence and Susceptibility Patterns

Abstract: Before 1985 at the Pitie-Salpetriere Hospital in Paris (2,400 beds), resistance to cefotaxime in clinical isolates of Enterobacteriaceae involved only species producing inducible class 1 beta-lactamase. Between November 1985 and April 1987, however, 62 isolates (57 of Klebsiella pneumoniae and five of Escherichia coli) showed decreased susceptibility to cefotaxime (mean MIC, 8-16 micrograms/mL). The transferability of cefotaxime resistance in E. coli K12 was demonstrated for 15 of 16 selected isolates. By isoelectric focusing using iodometric detection with 20 mg of ceftriaxone/100 mL and determination of substrate and inhibition profiles, three beta-lactamases mediating cefotaxime resistance were identified as SHV-2 (isoelectric point [pI] 7.6), CTX-1 (pI 6.3), and "SHV-2-type" or SHV-3 (pI 6.98). The three beta-lactamases hydrolyzed penicillins and cephalosporins (including cefotaxime and ceftriaxone) and were therefore designated "extended broad-spectrum beta-lactamases" (EBS-Bla). The enzymes conferred to derivatives a high level of resistance to amoxicillin, ticarcillin, piperacillin, and cephalothin and a decreased degree of susceptibility (i.e., MICs increased by 10- to 800-fold) to cefotaxime, ceftriaxone, ceftazidime, and aztreonam. These beta-lactamases did not affect the activity of cephamycins (cefoxitin, cefotetan, moxalactam) or imipenem. Synergy between clavulanate or sulbactam (2 micrograms/mL) and amoxicillin was greater against derivatives producing EBS-Bla than against those producing TEM-1, TEM-2, or SHV-1; this synergy was greater with clavulanate than with sulbactam against derivatives producing SHV-2 and the SHV-2-type enzyme but was similar with clavulanate and sulbactam against those producing CTX-1. A double-disk synergy test performed with cefotaxime and Augmentin disks (placed 30 mm apart, center to center) seemed a useful and specific test for the detection of strains producing EBS-Bla.

Growing group of extended-spectrum beta-lactamases: the CTX-M enzymes.

Abstract: The production of β-lactamases is the predominant cause of resistance to β-lactam antibiotics in gram-negative bacteria. These enzymes cleave the amide bond in the β-lactam ring, rendering β-lactam antibiotics harmless to bacteria. They are classified according to the scheme of Ambler et al. (2) into four classes, designated classes A to D, on the basis of their amino acid sequences, with classes A and C being the most frequently occurring among bacteria. Oxyimino-cephalosporins such as cefotaxime and ceftazidime, which are inherently less susceptible to β-lactamases, were introduced in the early 1980s to treat infections caused by gram-negative bacilli that were resistant to established β-lactams and that produced class A, C, and D β-lactamases. Their repetitive and increased use induced the appearance of resistant strains, which overproduced class C enzymes (42, 72) and/or which produced extended-spectrum β-lactamases (ESBLs), mainly those of class A but also those of class D (19, 61). Class A ESBLs hydrolyze oxyimino-cephalosporins and aztreonam but not 7-α-substituted β-lactams. They are generally susceptible to β-lactamase inhibitors (clavulanate, sulbactam, tazobactam). According to the functional classification scheme of Bush et al. (23), class A ESBLs are therefore clustered in group 2be, which can be subdivided on the basis of their activities against ceftazidime and cefotaxime as ceftazidimases (higher levels of hydrolytic activity against ceftazidime than against cefotaxime) and cefotaximases (higher levels of hydrolytic activity against cefotaxime than against ceftazidime), respectively (48). However, class A ESBLs form a heterogeneous molecular cluster comprising β-lactamases sharing 20 to >99% identity. The earliest class A ESBLs, which were reported from 1985 to 1987, differed from widespread plasmid-mediated TEM-1/2 and SHV-1 penicillinases by one to four point mutations, which extend their hydrolytic spectra (51, 90, 91). TEM and SVH ESBLs now comprise at least 130 members and have a worldwide distribution. Most of them are ceftazidimases, and only a few are cefotaximases. More recently, non-TEM and non-SHV plasmid-mediated class A ESBLs have been reported: ceftazidimases of the PER, VEB, TLA-1, and GES/IBC types and cefotaximases of the SFO-1, BES-1, and CTX-M types (8, 12, 13, 16, 31, 58, 62, 75, 76, 79, 81, 88, 96). The CTX-M β-lactamases are the most widespread enzymes. They were initially reported in the second half of the 1980s, and their rate of dissemination among bacteria and in most parts of the world has increased dramatically since 1995. This review focuses on the origin, epidemiology, clinical impact, enzymatic properties, and structural relationships of the CTX-M-type ESBLs.

Novel Carbapenem-Hydrolyzing β-Lactamase, KPC-1, from a Carbapenem-Resistant Strain of Klebsiella pneumoniae

Abstract: A Klebsiella pneumoniae isolate showing moderate to high-level imipenem and meropenem resistance was investigated. The MICs of both drugs were 16 microg/ml. The beta-lactamase activity against imipenem and meropenem was inhibited in the presence of clavulanic acid. The strain was also resistant to extended-spectrum cephalosporins and aztreonam. Isoelectric focusing studies demonstrated three beta-lactamases, with pIs of 7.2 (SHV-29), 6.7 (KPC-1), and 5.4 (TEM-1). The presence of bla(SHV) and bla(TEM) genes was confirmed by specific PCRs and DNA sequence analysis. Transformation and conjugation studies with Escherichia coli showed that the beta-lactamase with a pI of 6.7, KPC-1 (K. pneumoniae carbapenemase-1), was encoded on an approximately 50-kb nonconjugative plasmid. The gene, bla(KPC-1), was cloned in E. coli and shown to confer resistance to imipenem, meropenem, extended-spectrum cephalosporins, and aztreonam. The amino acid sequence of the novel carbapenem-hydrolyzing beta-lactamase, KPC-1, showed 45% identity to the pI 9.7 carbapenem-hydrolyzing beta-lactamase, Sme-1, from Serratia marcescens S6. Hydrolysis studies showed that purified KPC-1 hydrolyzed not only carbapenems but also penicillins, cephalosporins, and monobactams. KPC-1 had the highest affinity for meropenem. The kinetic studies also revealed that clavulanic acid and tazobactam inhibited KPC-1. An examination of the outer membrane proteins of the parent K. pneumoniae strain demonstrated that the strain does not express detectable levels of OmpK35 and OmpK37, although OmpK36 is present. We concluded that carbapenem resistance in K. pneumoniae strain 1534 is mainly due to production of a novel Bush group 2f, class A, carbapenem-hydrolyzing beta-lactamase, KPC-1, although alterations in porin expression may also play a role.

Outcome of Cephalosporin Treatment for Serious Infections Due to Apparently Susceptible Organisms Producing Extended-Spectrum β-Lactamases: Implications for the Clinical Microbiology Laboratory

Abstract: 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 (≤ 8 μg/ml) and to report ESBL-producing organisms as resistant to aztreonam and all cephalosporins (with the exception of cephamycins).