Detection of resistance due to inducible beta-lactamase in Enterobacter aerogenes and Enterobacter cloacae

Abstract

Thirty-six of 36 strains of Enterobacter cloacae and E. aerogenes with inducible (-lactamase developed resistance when cefoxitin (inducer) was added to cefuroxime disks. Constitutive 1-lactamase producers (n = 23) were all resistant to cefuroxime. Cefuroxime resistance correlated with the amount of induced or constitutive P-lactamase. Cefuroxime was a better indicator of induced resistance than cefamandole, cefazolin, cephalothin, ceftriaxone, cefotaxime, ticarcillin with or without clavulanic acid, or cefotetan. Induction by addition of cefoxitin to disks occasionally reduced zone sizes but not enough to change interpretations for ceftazidime, ceftizoxime, aztreonam, cefoperazone with or without sulbactam, and piperacillin with or without tazobactam. Most enterobacters were resistant to cefmetazole. The cefoxitin inducer-cefuroxime indicator method can be used in routine clinical laboratories to detect latent resistance due to chromosomally mediated inducible js-lactamase in enterobacters.

Prevalence of outer membrane porin alteration in beta-lactam-antibiotic-resistant Enterobacter aerogenes

“…As for the last group, a low level of cephalosporinase is detected in isolate 38 with no significant increase after induction whereas a weak production is noted for strain 17, which expressed an inducible cephalosporinase at a level equivalent to that observed in strain 38. Similar distribution of constitutive and inducible cephalosporinases has been previously reported in a clinical collection of E. cloacae and E. aerogenes (20), while no indication of outer membrane alterations has been mentioned by the authors. Our work also reports the detection of extended-spectrum ␤-lactamase with a pI of 6.5, possibly TEM-24, as previously described in E. aerogenes (12,28).…”

TEM-24 extended-spectrum β-lactamase-producing Enterobacter aerogenes: long-term clonal dissemination in French hospitals

“…It is important to detect Enterobacter strains producing ESBLs in a clinical laboratory, and to differentiate them from de‐repressed mutants, because they can be responsible for the spread of resistance genes in hospitals. However, difficulties have been noted in trying to detect ESBL production in Enterobacter over‐expressing chromosomally mediated cephalosporinase [36]. In our study, the easiest detection conditions by double disk synergy were with disks of cefepime and amoxycillin–clavulanic acid placed 30 mm apart.…”

Outbreak of TEM-24-producing Enterobacter aerogenes in an intensive care unit and dissemination of the extended-spectrum beta-lactamase to other members of the family enterobacteriaceae

“…Difficulty in detection of TEM-24 production is probably due to the presence of the chromosomally mediated cephalosporinase (3,11). The activity of ceftazidime was more efficiently restored by clavulanic acid than the activity of cefo-…”