Inhibition of Campylobacter coli and Campylobacter jejuni by antibiotics used in selective growth media

The ability of Campylobacter coli and Campylobacter jejuni to grow in the presence of antibiotics used in selective growth media was compared. MIC data for C. coli indicated that some strains were more susceptible to the antibiotics than were the C. jejuni strains tested. A reduction of greater than 1 log cycle in the numbers of cells growing on plates containing antibiotics was considered to be a marked level of inhibition. Only one of nine of the antibiotic combinations studied did not markedly inhibit most of the C. coli strains tested. Although one C. coli strain was not inhibited by any of the antibiotic combinations, the other six strains were inhibited for up to 7 log cycles. The addition of blood or growth supplements reduced but did not eliminate the inhibitory effect. The inhibition of laboratory strains of C. coli on media developed for the isolation of Campylobacter spp. indicates that the incidence of C. coli may be underestimated.