Prevalence of Newer β-Lactamases in Gram-Negative Clinical Isolates Collected in the United States from 2001 to 2002

Abstract

Newer ␤-lactamases such as extended-spectrum ␤-lactamases (ESBLs), transferable AmpC ␤-lactamases, and carbapenemases are associated with laboratory testing problems of false susceptibility that can lead to inappropriate therapy for infected patients. Because there appears to be a lack of awareness of these enzymes, a study was conducted during 2001 to 2002 in which 6,421 consecutive, nonduplicate clinical isolates of aerobically growing gram-negative bacilli from patients at 42 intensive care unit (ICU) and 21 non-ICU sites across the United States were tested on-site for antibiotic susceptibility. From these isolates, 746 screenpositive isolates (11.6%) were referred to a research facility and investigated to determine the prevalence of ESBLs in all gram-negative isolates, transferable AmpC ␤-lactamases in Klebsiella pneumoniae, and carbapenemases in Enterobacteriaceae. The investigations involved phenotypic tests, isoelectric focusing, ␤-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular analyses. ESBLs were detected only in Enterobacteriaceae (4.9% of all Enterobacteriaceae) and were found in species other than those currently recommended for ESBL testing by the CLSI (formerly NCCLS). These isolates occurred at 74% of the ICU sites and 43% of the non-ICU sites. Transferable AmpC ␤-lactamases were detected in 3.3% of K. pneumoniae isolates and at 16 of the 63 sites (25%) with no difference between ICU and non-ICU sites. Three sites submitted isolates that produced class A carbapenemases. No class B or D carbapenemases were detected. In conclusion, organisms producing ESBLs and transferable AmpC ␤-lactamases were widespread. Clinical laboratories must be able to detect important ␤-lactamases to ensure optimal patient care and infection control.

Extended-Spectrum β-Lactamases of the CTX-M Type Now in Switzerland

“…The prevalence rate of ESBL producers was 0.7%, which is very similar to that reported in the nearby country Austria in 2004 (9). However, this rate is lower than that reported in The Netherlands (7.8% [19]). Variable prevalence rates of ESBL producers may be related in part to differences in antibiotic policy (more quinolone used than ␤-lactams for treating community patients in Switzerland [10]) but also to differences in urban sizes (Paris area or Amsterdam versus Lausanne, for example).…”

Extended-Spectrum-β-Lactamase, AmpC, and Carbapenemase Issues

“…Isolates that coproduce both an ESBL and a high level of AmpC are becoming more common (24). With such pathogens, a positive CLSI (or equivalent) ESBL confirmatory test can usually be accepted as accurate, except for Acinetobacter spp.…”

Identification of nasal colonization with β-lactamase-producing enterobacteriaceae in patients, health care workers and students in Madagascar

“…Therefore, commercial hyplex ESBL ID PCR (amPLEX, Giessen, Germany) targeting bla CTX-M as the most frequent ESBL resistance mechanism in Madagascar [4] was applied to the swabs of a subset of 251 samples in Hamburg according to the manufacturer's instructions. As well as bla CTX-M [6], the hyplex ESBL kit also targets β-lactamases of the bla TEM -and bla SHV -types [5] as well as the bla OXA-1 carbapenemase in a consensus approach, though without specifi city for the expression of an ESBL phenotype. Positive signals of the bla CTX-M -PCR were correlated with cultural results on Brilliance ESBL agar, and positive signals of the β-lactamase consensus PCR, with the general growth of Enterobacteriaceae on MacConkey II agar.…”

“…In particular, extended-spectrum β-lactamase (ESBL)-positive Enterobacteriaceae are known to be prevalent in Madagascan hospital patients [1][2][3][4], including populations at particular risks such as newborns [1]. ESBL expression causes increased resistance to penicillins and cephalosporins, driven by a variety of molecular mechanisms [5,6]. Among known mechanisms, bla CTX-M expression (CTX = resistance to the WHO-listed antibiotic drug ceftriaxone, M = Munich, Germany, as the site of first description) is the most prevalent one in Madagascar, being detected in three out of four Madagascan ESBL-positive Enterobacteriaceae [4].…”