Antimicrobial Susceptibility and Sub-MIC Biofilm Formation of <i>Moraxella catarrhalis</i>Clinical Isolates under Anaerobic Conditions

A medium was developed to support the anaerobic growth and antimicrobial susceptibility testing of clinical Moraxella catarrhalis isolates. The MICs of clinical Moraxella catarrhalis isolates under anaerobic conditions were, in general, decreased as compared to atmospheric or capnophilic conditions, while the MBCs for all conditions were within a 2 fold concentration dilution. Biofilm formation was affected by the presence of sub-MIC concentrations of azithromycin and the tested quinolones with the exception of levofloxacin.