- Department of Biological Sciences Russian Federation
- Kelowna General Hospital Canada
- Royal Inland Hospital Canada
- Department of Pathology
- Department of Biological Sciences Belarus
- Interior Health Canada
- Department of Biological Sciences
- Thompson Rivers University Canada
BACKGROUND: Moraxella catarrhalis is a commensal organism of the respiratory tract that has emerged as an important pathogen for a variety of upper and lower respiratory tract infections including otitis media and acute exacerbations of chronic bronchitis. Susceptibility testing of M catarrhalis is not routinely performed in most diagnostic laboratories; rather, a comment predicting susceptibility based on the literature is attached to the report. The most recent Canadian report on M catarrhalis antimicrobial susceptibility was published in 2003; therefore, a new study at this time was of interest and importance. OBJECTIVE: To determine the susceptibility of M catarrhalis isolates from British Columbia to amoxicillin-clavulanate, doxycycline, clarithromycin, cefuroxime, levofloxacin and trimethoprimsulfamethoxazole. METHODS: A total of 117 clinical M catarrhalis isolates were isolated and tested from five Interior hospitals and two private laboratory centres in British Columbia between January and December 2012. Antibiotic susceptibility of M catarrhalis isolates was characterized using the Etest (E-strip; bioMérieux, USA) according to Clinical Laboratory Standards Institute guidelines. RESULTS: All isolates were sensitive to amoxicillin-clavulanate, doxycycline, clarithromycin, levofloxacin and trimethoprimsulfamethoxazole. One isolate was intermediately resistant to cefuroxime, representing a 99.15% sensitivity rate to the cephem agent. Cefuroxime minimum inhibitory concentrations (MICs) inhibiting 50% and 90% of organisms (MIC50 and MIC90) were highest among the antibiotics tested, and the MIC90 (3 μg/mL) of cefuroxime reached the Clinical Laboratory Standards Institute breakpoint of susceptibility. DISCUSSION: The antibiotic susceptibility of M catarrhalis isolates evaluated in the present study largely confirms the findings of previous surveillance studies performed in Canada. Cefuroxime MICs are in the high end of the sensitive range and the MIC50 and MIC90 observed in the present study are the highest ever reported in Canada. CONCLUSION: Although cefuroxime MICs in M catarrhalis are high, all agents tested showed antimicrobial activity, supporting their continued therapeutic and empirical use.
Moraxella catarrhalis has the ability to cause upper and lower respiratory tract infections. Typically, antibiotic susceptibility is not tested on isolation of the organism, but a reference document summarizing predicted susceptibilities is provided. The authors of this article aimed to determine the current susceptibilities of this organism in British Columbia, to update the predicted susceptibilites and ensure that appropriate antibiotic prescribing will occur.