DETERMINATION OF THE SUSCEPTIBILITY IN-VITRO OF 54 ISOLATES OF MYCOBACTERIUM-FORTUITUM AGAINST 3 FLUOROQUINOLONES USING 2 METHODS

The in vitro susceptibility to ofloxacin, norfloxacin and ciprofloxaci n or 54 Mycobacterium fortuitum isolates originating from clinical sam ples (7) of patients attending the Hospital Universitario de Canarias and Hospital del Torax, and from environmental (47) sources, were dete rmined. For this, two methods were used: dilution in agar with Middleb rook 7H10 Agar as a base medium culture, and broth microdilution, with Mueller-Hinton Broth without supplement. The different isolates under study revealed a uniform susceptibility by both methods against cipro floxacin. 100% inhibition was obtained from a Minimum Inhibitory Conce ntration (MIC) of 0.25 mu g/ml, and 2 mu g/ml of ciprofloxacin, for br oth microdilution and dilution in agar, respectively. For ofloxacin an d norfloxacin, all the isolates were inhibited at an MIC of 0.5 mu g/m l, by the broth microdilution method, which contrasted sharply with an MIC of 32 mu g/ml, in the case of dilution in agar. In this study, we have observed the existence of differences in the in vitro susceptibi lity of the isolates of M. fortuitum against the three fluoroquinolone s assayed, mainly for ofloxacin and norfloxacin, by both methods. We, therefore, consider it necessary to establish a standardized, reproduc ible assay method, for the study of sensitivity to atypical mycobacter ia.