Antimicrobial resistance in Haemophilus influenzae and Moraxella catarrhalis respiratory tract isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

Antimicrob Agents Chemother. 2003 Jun;47(6):1875-81. doi: 10.1128/AAC.47.6.1875-1881.2003.

Abstract

A total of 7,566 unique patient isolates of Haemophilus influenzae and 2,314 unique patient isolates of Moraxella catarrhalis were collected between October 1997 and June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among the 7,566 H. influenzae isolates, 22.5% produced beta-lactamase, while 92.4% of the 2,314 M. catarrhalis isolates produced beta-lactamase. The incidence of beta-lactamase-producing H. influenzae isolates decreased significantly over the 5-year study period, from 24.2% in 1997-1998 to 18.6% in 2001-2002 (P < 0.01). The incidence of beta-lactamase-producing M. catarrhalis isolates did not change over the study period. The overall rates of resistance to amoxicillin and amoxicillin-clavulanate for H. influenzae were 19.3 and 0.1%, respectively. The rank order of cephalosporin activity based on the MICs at which 90% of isolates were inhibited (MIC(90)s) was cefotaxime > cefixime > cefuroxime > cefprozil > cefaclor. On the basis of the MICs, azithromycin was more active than clarithromycin (14-OH clarithromycin was not tested); however, on the basis of the NCCLS breakpoints, resistance rates were 2.1 and 1.6%, respectively. Rates of resistance to other agents were as follows: doxycycline, 1.5%; trimethoprim-sulfamethoxazole, 14.2%; and chloramphenicol, 0.2%. All fluoroquinolones tested, including the investigational fluoroquinolones BMS284756 (garenoxacin) and ABT-492, displayed potent activities against H. influenzae, with MIC(90)s of < or = 0.03 microg/ml. The MIC(90)s of the investigational ketolides telithromycin and ABT-773 were 2 and 4 microg/ml, respectively, and the MIC(90) of the investigational glycylcycline GAR-936 (tigecycline) was 4 microg/ml. Among the M. catarrhalis isolates tested, the resistance rates derived by using the NCCLS breakpoint criteria for H. influenzae were <1% for all antibiotics tested except trimethoprim-sulfamethoxazole (1.5%). In summary, the incidence of beta-lactamase-positive H. influenzae strains in Canada is decreasing (18.6% in 2001-2002), while the incidence of beta-lactamase-positive M. catarrhalis strains has remained constant (90.0% in 2001-2002).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Anti-Bacterial Agents / pharmacology*
  • Anti-Bacterial Agents / therapeutic use
  • Canada
  • Drug Resistance, Multiple, Bacterial
  • Erythromycin / analogs & derivatives
  • Erythromycin / pharmacology
  • Female
  • Gram-Negative Bacterial Infections / microbiology*
  • Haemophilus influenzae / drug effects*
  • Haemophilus influenzae / isolation & purification
  • Humans
  • Influenza, Human / microbiology*
  • Ketolides*
  • Longitudinal Studies
  • Macrolides*
  • Male
  • Microbial Sensitivity Tests
  • Middle Aged
  • Minocycline / analogs & derivatives*
  • Minocycline / pharmacology
  • Moraxella catarrhalis / drug effects*
  • Moraxella catarrhalis / isolation & purification
  • Respiratory Tract Infections / microbiology*
  • Tigecycline
  • beta-Lactam Resistance
  • beta-Lactamases / metabolism

Substances

  • Anti-Bacterial Agents
  • Ketolides
  • Macrolides
  • Erythromycin
  • Tigecycline
  • beta-Lactamases
  • Minocycline
  • cethromycin
  • telithromycin