Antimicrobial resistance in Haemophilus influenzae and Moraxella catarrhalis respiratory tract isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002.
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).
Zhanel
George G
GG
Department of Medical Microbiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada.
Palatnick
Lorraine
L
Nichol
Kimberly A
KA
Low
Don E
DE
Hoban
Daryl J
DJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002170:Canada; D024901:Drug Resistance, Multiple, Bacterial; D004917:Erythromycin / Q000031:analogs & derivatives / Q000494:pharmacology; D005260:Female; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D007251:Influenza, Human / Q000382:microbiology*; D048628:Ketolides; D008137:Longitudinal Studies; D018942:Macrolides; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D001936:Moraxella catarrhalis / Q000187:drug effects* / Q000302:isolation & purification; D012141:Respiratory Tract Infections / Q000382:microbiology*; D000078304:Tigecycline; D018440:beta-Lactam Resistance; D001618:beta-Lactamases / Q000378:metabolism
D000900:Anti-Bacterial Agents; D048628:Ketolides; D018942:Macrolides; D004917:Erythromycin; D000078304:Tigecycline; D001618:beta-Lactamases; D008911:Minocycline; C405499:cethromycin; C106791:telithromycin