Coliforms and Enterobacteriaceae Isolates from Selected Foods

Abstract

We obtained coliform counts and Enterobacteriaceae counts using violet red bile agar (VRB) and VRB + 1% glucose (VRBG), respectively, of samples of five food products. From each set of VRB and VRBG plates, 28 to 40 “typical” colonies were randomly selected and identified by use of the R-B Enteric Differential System. A pure culture of each isolate was also subjected to the sequential tests for gas production in LST and BGLB broths (confirmed coliforms) and in EC broth at 45.5 C (fecal coliforms). IMViC reaction patterns of EC-positive cultures were also determined. Approximately 80% of the VRB isolates from broiler skin and from mechanically deboned poultry meat (MDPM) met all the criteria for fecal coliforms, whereas only 62.5% and 36.5%, respectively, of the VRBG isolates from these two products met these criteria. Fewer than 10% of the VRB and VRBG isolates from chicken pot pie, ground beef, or pork sausage produced gas in LST broth. The percentages of fecal coliforms and Escherichia coli (Type I or II) among the 179 VRB isolates were 34.1 and 33.5, respectively. Corresponding percentages for the 193 VRBG isolates were 20.7 and 19.7. E. coli was the predominant species isolated on both media from broiler skin and MDPM. Enterobacter agglomerans was the principal species isolated from chicken pot pie and pork sausage; Serratia liquefaciens predominated in ground beef.