Semisolid blood-free selective-motility medium for the isolation of campylobacters from stool specimens

Abstract

Isolation of Campylobacter jejuni and C. coli from stool specimens is done by growing campylobacter colonies on solid selective media with or without blood. However, recognition of these colonies can be difficult. Therefore, we decided to evaluate an isolation procedure based on the swarming of campylobacters through a semisolid medium. We developed a semisolid blood-free selective motility (SSM) medium which is composed of Mueller-Hinton broth with 0.4% agar and supplemented with cefoperazone (30 micrograms/ml) and trimethoprim (50 micrograms/ml). The SSM medium was compared with our previously described Butzler Medium Virion (Goossens et al., J. Clin. Microbiol. 24:840-843, 1986) and blood-free medium (Bolton and Coates, J. Appl. Bacteriol. 54:115-125, 1983) with cefoperazone (32 micrograms/ml) (Bolton et al., J. Clin. Pathol. 37:956-957, 1986). Of 1,890 routine stool specimens tested, 100 were found to be positive for campylobacters: 95 were recovered with the SSM medium, 94 with the Virion medium, and 90 with the blood-free medium. The SSM medium performed equally well whether it was incubated in the special incubator or the candle jar. Only 4.4 and 7.3% of the plates grew contaminating fecal flora when incubated in the special incubator and the candle jar, respectively. Clearly the SSM medium is easy, quick, cheap, sensitive, and more selective than any other medium which has been developed so far and does not require the addition of blood. We believe that this medium has a future in the routine microbiology laboratory in developed as well as in developing countries.