Evaluation of the in vitro activity of seven selected antimicrobial agents to be used for the isolation of human intestinal spirochaetes.

This study aimed at making a comparative assessment of the growth of pure cultures of Human Intestinal Spirochaetes (HIS) in a control medium without antibiotics and in media including antibiotics (spectinomycin, rifampin, colistin, polymyxin B, amphotericin B, vancomycin, spiramycin) whose use had been indicated in the literature in connection with the isolation of HIS or animal intestinal spirochaetes. All the strains of HIS tested grew in media to which appropriate concentrations of those drugs had been added giving a final number of CFU/ml +/- 10 times the number of CFU/ml observed in the control medium. These results indicate that a selective medium to be used for the isolation of HIS may include appropriate concentrations of one or more of the following antibiotics: spectinomycin (100-1,000 micrograms/ml), rifampin (10-30 micrograms/ml), vancomycin (6.25 micrograms/ml), colistin (6.25 micrograms/ml), polymyxin B (5 micrograms/ml), spiramycin (1-10 micrograms/ml) and amphotericin B (0.05-35 micrograms/ml).

Cooperative haemolysis between weakly beta-haemolytic human intestinal spirochaetes and Staphylococcus aureus.

Weakly beta-haemolytic spirochaetes related to human intestinal spirochaetosis produced a cooperative haemolysis together with S. aureus consisting of an enhanced haemolysis in the zone of the spirochaetal growth which was overlapped by the zone of activity of the staphylococcal beta-haemolysin. The cooperative haemolysis was observed in sheep blood agar media when the concentration of spirochaetes ranged from 1.5 x 10(3) to 1.5 x 10(8) CFU/ml and the concentration of S. aureus from 4 x 10(3) to 4 x 10(8) CFU/ml. With the increase of the distance between the streaks of the spirochaetes and S. aureus from 3 to 10 mm, the period of incubation needed to observe the cooperative haemolysis also increased from 18 to 72 hours. When the spirochaetes and S. aureus were streaked at the same time and when S. aureus was streaked earlier than the spirochaetes, the phenomenon was observed after anaerobic incubation of the plates for 24-72 hours but not after incubation in 10% CO2 under atmospheric conditions. A cooperative haemolysis was also observed between S. aureus and spirochaetes related to the porcine and avian intestinal spirochaetosis and the spirochaete causing swine dysentery when the same experimental conditions were used which allowed an observation of the phenomenon involving human spirochaetes and S. aureus.