USE of OXYRASETM ENZYME IN ENRICHMENTS to ENHANCE the RECOVERY of ESCHERICHIA COLI O157:H7 FROM CULTURE MEDIA and GROUND BEEF1

Abstract

OxyraseTM membrane fraction was tested as an additive to nonselective BHI enrichment broth (0.1 unit/ml) to observe effects on growth of three strains of pathogenic Escherichia coli, including O157.H7 serotypes, and one nonpathogenic strain in culture broth and autoclaved ground beef systems. OxyraseTM enhanced the growth of all three pathogenic strains (inoculated at <1 cell/ml) in the broth system by shortening the lag phase period by 2–3 h. Growth of the nonpathogenic E. coli strain tested was suppressed by the presence of OxyraseTM during the initial 4 h of incubation at 37C in both broth and autoclaved ground beef systems. Stimulatory effects of the enzyme added at 0.1 unit/ml were not observed in autoclaved meat systems when E. coli strains were inoculated at 1–100 cells/g of meat during 24 h of incubation at 37C.BHI broth alone and used as a nonselective enrichment for autoclaved and fresh ground beef was evaluated to observe the effect of OxyraseTM on the oxidation‐reduction potential (Eh) of each system after 0, 4 and 18 h of incubation at 37C. OxyraseTM slightly lowered Eh after 4 and 18 h in BHI broth and fresh ground beef (in BHI). However, no Eh‐decreasing effects were seen at this time in systems containing autoclaved ground beef which may explain the lack of a stimulatory effect of OxyraseTM on growth of E. coli in autoclaved ground beef.