Corynebacterium species are increasingly being implicated in
foreign-body infections and in immunocompromised-host
infections. However, there are no specific recommendations on the method or the criteria to use in order to determine the in vitro activities of the
antibiotics commonly used to treat
Corynebacterium infections. The first aim of our study was to compare the susceptibilities of various species of Corynebacterium to
vancomycin,
erythromycin, and
penicillin by using a broth microdilution method and a disk diffusion method. Second, the activity of
penicillin against our isolates was assessed by using the interpretative criteria recommended by the National Committee for Clinical Laboratory Standards for the determination of the susceptibility of streptococci and Listeria monocytogenes to
penicillin. Overall, 100% of the isolates were susceptible to
vancomycin, while considerable variations in the activities of
erythromycin and
penicillin were noted for the different species tested, including the non-Corynebacterium jeikeium species. A good correlation in the susceptibilities of
vancomycin and
erythromycin between the disk diffusion and the microdilution methods was observed. However, a 5% rate of major or very major errors was detected with the Listeria criteria, while a high rate of minor errors (18%) was noted when the streptococcus criteria were used. Our findings indicate considerable variations in the activities of
erythromycin and
penicillin against the various species of Corynebacterium. Because of the absence of definite recommendations, important discrepancies were observed between the methods and the interpretations of the
penicillin activity.