SELECTION OF OPTIMUM LABORATORY TESTS FOR THE IDENTIFICATION OF MORAXELLA-CATARRHALIS

We evaluated a variety of conventional and rapid tests and examined th e erythromycin susceptibility of a collection of Moraxella catarrhalis and commensal neisseria strains in order to determine the optimum met hod for routine identification. One hundred and fifty three strains we re tested by Gram stain, catalase, oxidase, carbohydrate degradation b y two methods and the presence of esterases using indoxyl acetate, 4-m ethylumbelliferyl butyrate (MUB), Tween 80 and tributyrin as substrate s. Erythromycin MICs and zone diameters around 1, 5 and 15 mu g discs were determined by the NCCLS method for 151 of the strains. A combinat ion of Gram stain, oxidase and either indoxyl acetate, spot MUB or tri butyrin hydrolysis test proved to be reliable and potentially the most convenient for routine testing. MICs and zone diameters easily distin guished between the erythromycin-sensitive M. catarrhalis and the eryt hromycin-resistant commensal neisserias and would provide confirmation of identification if used for susceptibility testing.