Susceptibility testing of fastidious organisms

The NCCLS has published guidelines for the susceptibility testing of fastidious organisms. Following these guidelines for the assessment of a new trinem, sanfetrinem (GV 104326), against Neisseria spp. we obtained unexpectedly high MICs and therefore undertook a study to compare MICs obtained on a variety of media. These data suggest that Iso-Sensitest agar supplemented with 20 mg/L NAD and 5% whole horse blood would be appropriate for sensitivity testing compounds affected by the presence of L-cysteine. Previous data published from this department have also shown that this medium is suitable for testing other fastidious organisms such as Streptococcus pneumoniae and Haemophilus influenzae. These data suggest that supplemented Iso-Sensitest agar, the medium chosen by the BSAC Working Party on antibiotic sensitivity testing, would be appropriate and that MIC results obtained with this medium would be comparable to those obtained on the NCCLS recommended media.