Beta-lactamase activity against H. influenzae exhibiting amoxicillin (with or without clavulanate) resistance phenotypes/genotypes

Abstract number: P2078

Cercenado E., Cafini F., Gené A., Marco F., Martínez-Martínez L., Alou L., Gómez-Garcés J.L., Casal M., Aguilar L.

Objective: To explore the in vitro activity of amoxicillin/clavulanate (AMC), cefuroxime (CXM), cefdinir (CDR), cefotaxime (CTX), and cefditoren (CDN) against 150 isolates belonging to the b-lactamase negative ampicillin (AMP)-resistant (BLNAR) and b-lactamase positive AMC-resistant (BLPACR) H. influenzae resistance phenotypes.

Methods: In vitro susceptibility of 126 BLNAR (64 with ampicillin MIC=2 mg/l, and 62 with MICgeqslant R: gt-or-equal, slanted4 mg/l) and 24 BLPACR (19 with AMC MIC=4 mg/l, and 5 with AMC geqslant R: gt-or-equal, slanted8 mg/l) isolates from 6 Spanish hospitals in 2004–2007, was determined by microdilution following CLSI recommendations. CLSI susceptibility breakpoints (mg/l) considered were: AMP leqslant R: less-than-or-eq, slant1; AMC leqslant R: less-than-or-eq, slant4/2, CXM leqslant R: less-than-or-eq, slant4, CDRleqslant R: less-than-or-eq, slant1, and CTX leqslant R: less-than-or-eq, slant2. No CLSI breakpoints are defined for CDN. Mutations in the ftsI gene encoding PBP3 were determined by PCR amplification and direct sequencing.

Results: MIC50 (mg/l), MIC90 (mg/l), and % susceptibility (%S) are shown in the Table.

A total of 90.5% BLNAR (AMP MIC geqslant R: gt-or-equal, slanted2 mg/l) and 79.2% BLPACR (AMC MIC geqslant R: gt-or-equal, slanted4 mg/l) phenotype isolates tested exhibited single or multiple mutations in the ftsI gene, being N526K (present in 112 isolates), V545I (103 isolates), D350N (83 isolates) and A502T/V (69 isolates) the most frequent.

Conclusion: The range of intrinsic activity in terms of MIC90 values was: CDN > CTX > AMC = CDR > CXM. CDN exhibited potent activity (2–4 times higher than CTX) against all H. influenzae isolates exhibiting a BLNAR/BLPACR phenotype that showed low susceptibility rates to AMC, CDR and CXM.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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