GROWTH OF ESCHERICHIA-COLI O157-H7 IN THE PRESENCE OF PSEUDOMONAS-FLUORESCENS IN SKIMMED-MILK AT 7 OR 25C

Escherichia coli O157:H7 STCC 4076, E. coli O157:H7 STCC 4267 and E. c oli STCC 515 were cultured alone or in combination with Pseudomonas fl uorescens STCC 378 at 7C or 25C in 10% reconstituted skimmed milk. Cul ture pH and bacterial population densities were monitored over 40 days . Both E. coli O157:H7 strains grew well after 40 days of incubation a t 70 with final pH values between 4.86-4.53. At 25C, both E. coli O157 :H7 strains grew during 20 days with final pH values of 4.00-4.14. The pH of the different cultures of this study decreased more at 25C than at 7C. The results suggest that P. fluorescens may inhibit the growth of the other bacteria present in milk at 70, but this inhibition is w eak. In contrast, the growth of E. coli O157:H7 strains in the presenc e of P. fluorescens appears to be slightly enhanced during most of the incubation period at 25C.