Selection of Bacteriophages active on Escherichia coli O157:H7 under acidic conditions.

OLAYA PASSARELL, M.J.; HEBERT, E.M.; BRABBAN, A.; KUTTER, E.; RAYA, R.R.

Olympia, WA.

Congreso; 17th Evergreen internacional Phage Biology Meeting.; 2007

The Evergreen State College

Strains of the food-borne pathogen Escherichia coli O157:H7 can withstand extremely acidic environments for long periods. In addition, O157:H7 cells exposed  to organic acids (acid-adapted cells) are more resistant to a subsequent strong acidic challenge; four systems, among them the glutamate- and the arginine-dependent systems, contribute to the acid resistance of these cells. In recent years, bacteriophages have generated increasing interest as a potential control against bacterial pathogens including O157:H7. In this study we evaluated the efficiency of plaquing (EOP) under acidic conditions of seven virulent bacteriophages active on the O157:H7 strain NCTC 12900 (ATCC 700728). Spot test experiments on NCTC 12900 with phages CEV2, 6, 65, 77, 120, Rxpp and XnR, phages that were isolated from sheep fecal material, were conducted in LB agar, containing or not arginine (0.6 mM) or glutamate (0.57 mM), at different pH values (4.5, 5.0, 5.5, and 7.0). Five microliters of each phage (dilutions 100 to 10-8) were spotted on NCTC 12900 lawn, preprared in LB soft agar (0.6%) with cells grown overnight in LB broth (pHi = 7.0) or LB plus the buffer MES (100 mM; pHi = 5.0). Similar phage titers for each phage were observed in the range of pH 5.0 to 7.0 (EOP = 1]. However at pH 4.5, an EOP of 1 was only observed for phage 120, while EOP values of 10-2-10-3 were obtained for phages 6 and 65 and EOP <10-8 for the rest of the phages. No effect of the glutamate- and arginine-dependent acid resistance systems of NCTC 12900 cells on the efficiency of plaquing was observed. The selection of bacteriophages active on E. coli O157:H7 under low-pH conditions might contribute to combat this important food pathogen in acidic foods.