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 p eptone water, cefsulodin-irgasan-novobiocin broth base or supplemented broth base (CIN). The lag phase durations and growth rates under thes e conditions were determined by linear regression analysis. In pure cu lture, 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 than P- strains at 37 degrees C, probably due to the increased metabolic burden entailed in the mainten ance of the virulence plasmid. In the most selective medium, i.e. CIN broth, P+ strains grew significantly faster than P-. This finding sugg ests that possession of virulence plasmid confers an enhanced ability to grow in the presence of selective agents. In meat cultures, both st rains had longer lag phases than in equivalent pure cultures, with lon ger lag phases noted at 37 than at 25 degrees C. No significant differ ences were observed between the length of lag phases of P+ and P- stra ins in meat culture. Both strains of Y. enterocolitica displayed faste r growth rates in meat cultures than in pure cultures, indicating that one or more components of meat enhanced the growth of this organism. The effects and interaction of incubation temperature, enrichment brot h and meat on the growth kinetics of plasmid-bearing and plasmid-cured Y. enterocolitica strains are discussed.