title: Apparent plateau in beta-lactamase production among clinical isolates of Haemophilus influenzae and Moraxella catarrhalis in the United States: results from the LIBRA Surveillance initiative.
abstract: Haemophilus influenzae (n=2791) and Moraxella catarrhalis (n=1249) isolated from patient specimens during 1999 were collected from 290 laboratories participating in a moxifloxacin surveillance study as part of the LIBRA Surveillance initiative. Isolates were tested for in vitro susceptibility to a panel of agents suitable for the treatment of respiratory tract infections. beta-Lactamase production was identified in 32.2% of H. influenzae and 94.2% of M. catarrhalis. These percentages differed by less than 1.5% from results of a study conducted in 1997-1998 and were similar to results from other recent US surveillance studies. Resistance among H. influenzae to trimethoprim-sulphamethoxazole increased considerably, from 2% in the 1997-1998 study (n=6588 H. influenzae) to 15.5% in the current study. One isolate of H. influenzae had an MIC of 8 mg/l to both levofloxacin and moxifloxacin; all other isolates had MICs of < or =0.5 mg/l and < or =0.25 mg/l, respectively. beta-Lactamase production was found to confer ampicillin resistance in nearly all isolates. For M. catarrhalis, beta-lactamase-negative isolates had MICs < or =0.12-0.25 mg/l for ampicillin and < or =0.03-0.12 mg/l for ceftriaxone. In contrast, beta-lactamase production resulted in MICs of < or = 0.12->16 mg/l for ampicillin and < or = 0.03-4 mg/l for ceftriaxone. All M. catarrhalis had MICs < or =0.12 mg/l for moxifloxacin and < or =1 mg/l for levofloxacin. In summary, antimicrobial susceptibilities and the prevalence of beta-lactamase production in H. influenzae and M. catarrhalis in the United States has remained essentially unchanged from 1997-1998 to 1999.
authors.affiliation: Focus Technologies, Koninginneweg 11, 1217 KP, Hilversum, The Netherlands. mjones@focusanswers.com
authors.forename: Mark E
authors.initials: ME
authors.lastname: Jones
authors.forename: James A
authors.initials: JA
authors.lastname: Karlowsky
authors.forename: Renée
authors.initials: R
authors.lastname: Blosser-Middleton
authors.forename: Ian A
authors.initials: IA
authors.lastname: Critchley
authors.forename: Clyde
authors.initials: C
authors.lastname: Thornsberry
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Sahm
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D006192:Haemophilus Infections / Q000382:microbiology; D006193:Haemophilus influenzae / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D001936:Moraxella catarrhalis / Q000187:drug effects / Q000201:enzymology*; D016870:Neisseriaceae Infections / Q000382:microbiology; D014481:United States; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000378:metabolism*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases