Cephalexin-supplemented Jones-Kendrick charcoal agar for selective isolation of Bordetella pertussis: comparison with previously described media

Abstract

Four agar media, Jones-Kendrick (JK) charcoal agar unsupplemented, JK agar supplemented with 0.5 U of penicillin per ml, JK medium supplemented with 2.5 micrograms of methicillin per ml, and JK medium supplemented with 40 micrograms of cephalexin per ml, were evaluated to determine their ability to support growth of Bordetella pertussis, their ability to selectively inhibit normal pharyngeal flora while maintaining growth of B. pertussis, and their stability during storage. Five stock cultures of B. pertussis were plated on each of the media. Penicillin- and cephalexin-supplemented media were more inhibitory for early growth of B. pertussis than was medium supplemented with methicillin. However, after 5 days of incubation at 35 degrees C, all media supported good growth of this organism. When employed to detect B. pertussis in sham specimens, prepared by mixing normal pharyngeal material with each of the five B. pertussis stock cultures, the medium containing cephalexin was judged superior to all other media tested in its combined ability to suppress the growth of normal pharyngeal flora and to allow early detection of Bordetella colonies. All media tested retained their efficacy after 9 weeks of storage at 2 to 8 degrees C.