A study of the growth kinetics of Yersinia enterocolitica serotype O:3 in pure and meat culture systems.

The growth kinetics of a virulence plasmid-bearing (P+) and a plasmid-cured (P-) strain of Yersinia enterocolitica serotype O:3 in pure and meat culture were investigated. Growth studies were carried out at 25 and 37 degrees C in supplemented phosphate-buffered saline, buffered peptone water, cefsulodin-irgasan-novobiocin broth base or supplemented broth base (CIN). The lag phase durations and growth rates under these conditions were determined by linear regression analysis. In pure culture, under most sets of equivalent conditions, P+ and P- strains had similar lag phase durations. However, under one set of conditions, i.e. CIN broth at 37 degrees C, the lag phase duration of the P+ strain was significantly longer than P-. In all but the most selective medium, P+ strains had slower growth rates that P- strains at 37 degrees C, probably due to the increase metabolic burden entailed in the maintenance of the virulence plasmid. In the most selective medium, i.e. CIN broth, P+ strains grew significantly faster than P-. This finding suggests that possession of virulence plasmid confers an enhanced ability to grow in the presence of selective agents. In meat cultures, both strains had longer lag phase than in equivalent pure cultures, with longer lag phases noted at 37 than at 25 degrees C. No significant differences were observed between the length of lag phases of P+ and P strains in meat culture. Both strains of Y. enterocolitica displayed faster growth rates in meat cultures than in pure cultures, indicating that one of more components of meat enhanced the growth of this organism. The effects and interaction of incubation temperature, enrichment broth and meat on the growth kinetics of plasmid-bearing and plasmid-cured Y. enterocolitica strains are discussed.