Susceptibility Test Methods: Fastidious Bacteria*

Most fastidious bacteria do not grow satisfactorily in standard in vitro susceptibility test systems that use unsupple-mented media. Clinical and Laboratory Standards Institute (CLSI) has also published an approved guideline for testing infrequently isolated or fastidious bacteria including Abiotrophia spp., Granulicatella spp., Aeromonas spp., Plesiomonas spp., Bacillus spp. (not B. anthracis), Campylobacter jejuni/coli, Corynebacterium spp., Erysipelothrix rhusiopathiae, the HACEK group, Lactobacillus spp., Leuconostoc spp., Listeria monocytogenes, Moraxella catarrhalis, Pasteurella spp., Pediococcus spp., and Vibrio spp. In addition to conventional MIC test methods (e.g., agar dilution or broth dilution methods), the Etest MIC determination method has been used to test many types of fastidious bacteria. The limitations of this method include its cost and lack of clearance by the U.S. Food and Drug Administration (FDA) for testing many less commonly encountered fastidious bacteria. This chapter summarizes the standard methods recommended by CLSI for antimicrobial susceptibility testing of Streptococcus spp. (including S. pneumoniae), H. influenzae, N. gonorrhoeae, and N. meningitidis. Methods for testing the infrequently isolated or fastidious bacteria included in the CLSI M45 guideline are summarized to include testing potential agents of bioterrorism. The incidence of resistance, test methods, and indications for testing and the reporting of results are provided.