The effect of temperature and selective agents on the growth of Yersinia enterocolitica serotype O : 3 in pure culture

This study examined the individual and combined effects of the selective ag ents normally present in Yersinia-selective agar (i.e. cefsulodin, irgasan and novobiocin) on the growth kinetics of plasmid-bearing (P+) and plasmid- cured (P-) Yersinia enterocolitica serotype O:3 at 25 and 37 degrees C. Gro wth studies were carried out in pure culture, and the data obtained were su bjected to linear regression analysis to determine lag phase duration(s) an d growth rates of the examined strains. In general, the presence of selecti ve agents increased the duration of the lag phase at 37 degrees C, with lon ger lag phases noted in all cases in which two or more selective agents wer e present. Growth rates in CIN broth base (CIN NA) and CIN NA plus commerci al supplement (SR 109) (CIN) were faster at 37 than 25 degrees C, but in so me cultures of incomplete CIN NA broth with less than three supplements add ed, growth tended to be faster at 25 than 37 degrees C. Generally, plasmid- bearing strains grew slower than plasmid-cured strains in most media at 37 degrees C due to virulence plasmid expression retarding growth. In some ins tances at 37 degrees C, it was observed that the growth rates of both plasm id-bearing and plasmid-cured strains were comparable, indicating the influe nce of added selective agent/s negating any effects associated with virulen ce plasmid expression. The effects of selective agents, incubation temperat ure and virulence plasmid carriage on the growth kinetics of Y. enterocolit ica are discussed.