Comparative growth of pure cultures of human intestinal spirochaetes on six selective media

The growth of pure cultures of 24 human intestinal spirochaetes (HIS) was analysed comparatively in six selective media with antibiotics and in a control medium without antibiotics. The selective media SR and SP were the only two media among the six tested which allowed the growth of all the strains studied. These media contained spectinomycin (400 micrograms/ml) and rifampin (30 micrograms/ml) (SR), and spectinomycin (400 micrograms/ml) and polymyxin B (5 micrograms/ml) (SP), respectively. Moreover, most of the strains tested showed in these two media a number of CFU/ml equal to, or, for a few strains, not more than ten-fold lower than that observed in the control medium. The other four selective media tested were: SRVC (spectinomycin 200 micrograms/ml; rifampin 12.5 micrograms/ml; vancomycin 6.25 micrograms/ml; colistin 6.25 micrograms/ml), CSp (colistin 6.25 micrograms/ml; spiramycin 25 micrograms/ml), SRSp (spectinomycin 200 micrograms/ml; rifampin 12.5 micrograms/ml; spiramycin 25 micrograms/ml) and SRVCSp (spectinomycin 200 micrograms/ml; rifampin 12.5 micrograms/ml; vancomycin 6.25 micrograms/ml; colistin 6.25 micrograms/ml; spiramycin 25 micrograms/ml). The growth of most of the spirochaetes was strongly reduced in the media SRVC, CSp, SRSp and SRVCSp. Furthermore, several of the 24 HIS examined did not grow in the medium SRVC (3 spirochaetes, 11%), CSp (15 spirochaetes, 62%), SRSp (17 spirochaetes, 70%), SRVCSp (19 spirochaetes, 79%). The results reported in this paper indicate that the media SR and SP, of the six selective media tested, may profitably be used in the isolation of HIS as they did not significantly affect the growth of the HIS tested.