Abstract
Two anaerobic (A1 and A2), 1 selective (S1), and 3 conventional (C1, C2, and C3) transport media formulations were compared for their capacity to maintain the viability of Serpulina (Treponema) hyodysenteriae. Initial experiments compared the recovery of S. hyodysenteriae from pure cultures held in each transport medium for 0.5, 1, 2, 3, 5, and 7 days at −40 C, 4 C, 25 C, and 36 C. Subsequent experiments compared each transport medium for maintenance of S. hyodysenteriae in fecal specimens obtained from experimentally infected pigs after holding for up to 7 days at 25 C. In each experiment, the viability of S. hyodysenteriae in each transport medium incubated at each temperature and for each period was determined by inoculating the transport medium onto either trypticase soy agar with 5% sheep blood or selective BJ agar and incubating at 42 C anaerobically. Viability and fecal flora contamination were evaluated blindly after 2-, 4-, and 6-day incubation periods. At −40 C, recovery of viable S. hyodysenteriae from pure culture did not differ among the transport media from 0.5 to 7 days, and all of the transport media consistently maintained the viability of the spirochetes for 7 days. At 4 C, the anaerobic and selective transport media maintained the viability of pure cultures of S. hyodysenteriae significantly better than did the conventional transport media group at day 7 (P = 0.019). At the same temperature, the anaerobic media maintained viability better than did the conventional media at 5 days (P < 0.042). At 25 C, the anaerobic transport media were significantly better than the conventional transport media at maintaining the viability of pure cultures of the spirochetes at 2, 3, and 5 days (P < 0.018) and were significantly better than the selective medium at 3 days (P = 0.012). At 36 C, the recovery of viable spirochetes was significantly better with the anaerobic transport media than with both the conventional media for days 2–7 (P < 0.006) and the selective medium for days 3–7 (P < 0.049). Fecal specimens held in transport media Al and C1, as a group, had significantly higher viability than those held in the other transport media formulations taken as a group at all incubation times, except 0.5 day (P < 0.0046). Contamination of selective BJ medium by fecal flora was markedly higher after holding fecal specimens in conventional transport media than in anaerobic and selective transport media. In a dilution trial of a pure culture of spirochetes, transport media Al and A2 maintained the viability of 108 S. hyodysenteriae for 7 days; however, medium Al was 10–100-fold more effective than medium A2 when lower initial concentrations of spirochetes were sampled. In a dilution trial of a fecal specimen, medium Al maintained the viability of 101 spirochetes for 2.5 days compared with 103 with medium C1. Overall, media A1 and C1 were the most satisfactory transport media for recovery of viable S. hyodysenteriae from fecal specimens held at 25 C for up to 7 days.