IN-VITRO COMPARISON OF BOVINE MASTITIS AND FECAL ESCHERICHIA-COLI ISOLATES

In vitro methods were used to test the hypothesis that Escherichia col i from bovine mastitis are essentially no different from isolates from bovine feces. Fifty E. coli isolates from bovine mastitic milk, 50 fr om feces of mastitic cows and 50 from feces of healthy cows were compa red with respect to biochemical properties and certain potential virul ence factors. There were no significant differences among the groups i n tests for biotype; production of colicins, colicin V, or Vero cell c ytotoxicity; and growth in 90% gnotobiotic calf serum or 90% normal mi lk whey. Resistance to killing in 90% gnotobiotic calf serum varied fr om 66 to 84%. Most isolates grew in normal whey: the percentage in a g roup varied from 86 to 96. Mastitic milk isolates were significantly d ifferent from the fecal isolates in adonitol fermentation (P less than or equal to 0.006), production of aerobactin (P less than or equal to 0.026), and ability to grow in 90% mastitic whey (P less than or equa l to 0.00004). However, only 40% of mastitis E. coli fermented adonito l and only 20% produced aerobactin. Ninety-six percent of mastitic mil k E. coli grew in mastitic whey, whereas 64% and 60%, respectively, of mastitic fecal and normal fecal isolates grew in this medium. It is c oncluded that none of the properties that were investigated constitute potential virulence factors or markers for ability to induce mastitis ; the data are consistent with the hypothesis that mastitic E. coli ar e simply opportunistic pathogens.