Enterobacteriaceae Identification from Stock Cultures and High Moisture Foods with a Four-Hour System (API Rapid E)

Abstract

The API Rapid E is a 4-h system for the identification of Enterobacteriaceae that has not previously been evaluated with food isolates. A total of 232 cultures, representing 13 genera of Enterobacteriaceae, was used in this study; 47 were known stock cultures and 185 were freshly isolated from raw foods (broiler carcasses, chicken sausage, hamburger, scallops and shrimp). Each food isolate was inoculated into the API Rapid E and also into two other miniaturized systems (Micro-ID and API-20E) which served as the reference. API Rapid E correctly identified 219 (94.4%) of the cultures to species. Ten of the thirteen errors in identification occurred with Enterobacter spp. because of false-negative reactions with the Voges-Proskauer test. The predominant Enterobacteriaceae encountered in each food were Escherichia coli (broiler carcasses), Serratia marcescens (chicken sausage), Enterobacter aerogenes (hamburger), Enterobacter cloacae (scallops) and Klebsiella oxytoca (shrimp). The degree of accuracy with the variety of organisms tested in this study coupled with the 4-h incubation should make the API Rapid E a practical alternative to conventional procedures for the practicing food microbiologist.