In vitro susceptibility of Mycobacterium fortuitum to cefoxitin

The in vitro susceptibility of Mycobacterium fortuitum to cefoxitin was studied by agar dilution, broth dilution, and disk diffusion methods. Of 13 isolates, 11 were found to be susceptible by disk diffusion. At a concentration of 25 microgram/ml or lower, all 13 isolates were inhibited when tested by broth dilution, but only 12 of 13 isolates were inhibited when tested by agar dilution.