Molecular Epidemiological Study of Moraxella catarrhalis Isolated from Nosocomial Respiratory Infection Patients in a Community Hospital in Japan

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Background Moraxella catarrhalis, occasionally, plays the essential role in nosocomial respiratory infection (NRI). Few studies have reported the route by which this organism spreads in a nosocomial infection outbreak. We identified characteristics of the strains isolated from NRI and attempted to reveal the potential nosocomial transmission routes. Methods A follow-up study has been performed in a Japanese community hospital between July 2002 and January 2003. M. catarrhalis clinical isolates were identified and β-lactamase production test as well as the minimal inhibitory concentrations (MICs) have been examined. Pulsed-field gel electrophoresis (PFGE) and the multi locus sequence typing method (MLST) have been introduced as the effective "fingerprinting" methods. Results A total of 29 strains were isolated from 17 participants; 7 independent DNA fragment patterns were detected by PFGE. Pattern B (defined in this study) was dominant, and was detected both in strains from a health care worker (HCW) and inpatients. In the 9 selected strains analyzed by MLST, 7 unique MLST types were identified, which showed the congruence with the results of PFGE results. Conclusion Epidemiological analysis proved the transmission route from patient to patient, and suggested that more studies should be focused on identifying the possible transmission route between HCWs and inpatients.