Microflora Recovered from Foods on Violet Red Bile Agar with and without Glucose and Incubated at Different Temperatures

Abstract

Counts and taxonomic distribution of typical colonies on violet red bile agar (VRB) and VRB with 1 o/o glucose~ (VRBG) incubated at 45, 35, 20, 7 and 1 °C from 23 retail food samples were compared. Aerobic plate counts were also obtained at each incubation temperature. Samples included fresh meats, processed meats, frozen processed products and fresh vegetables. Overall mean VRBG counts were slightly higher than VRB counts at each incubation temperature although there was some variation according to sample type. No significant differences (p>0.05) between the two media were noted overall or for any food type. Highest counts for VRB and VRBG generally occurred at 20°C incubation followed by 35, 7, 45 and 1 °C; counts at 20 and 35°C were not significantly different (p>0.05). The taxonomic distribution of typical colonies varied according to incubation temperature and sample type but there were few differences between VRB and VRBG for a given sample and incubation temperature. At 45°C, Escherichia coli was the most frequently recovered organism from both media overall but Klebsiella pneumoniae, Erwinia herbicola or Enterobacter cloacae predominated in many samples. Serratia marcescens and Erwinia herbicola comprised the majority of isolates from both media at 35, 20, 7 and 1 °C with taxonomic diversity being greatest at 35 and 20°C. The coliform count using violet red bile agar (VRB) has been used traditionally as an indicator of fecal contamination and/or sanitary quality in various foods while the total Enterobacteriaceae count using VRB with 1% glucose (VRBG) has received increased attention in recent years as an indicator system (1,4,5,12-15,17.22.23). The validity of VRB or VRBG counts as indicators of sanitary quality and the taxonomic distribution of bacteria forming typical colonies on these media have 1