Frequency of indicator bacteria, Salmonella and diarrhoeagenic Escherichia coli pathotypes on ready-to-eat cooked vegetable salads from Mexican restaurants

Abstract

The presence of coliform bacteria, faecal coliforms, Escherichia coli, diarrhoeagenic E. coli pathotypes (DEP) and Salmonella were determined in ready-to-eat cooked vegetable salads (RECS) from restaurants in Pachuca city, Mexico. The RECS were purchased from three types of restaurants: national chain restaurants (A), local restaurants (B) and small restaurants (C). Two restaurants for each A and B, and three for C, were included. Forty RECS samples were purchased at each A and B restaurant and 20 at each C restaurant. Of the overall total of 220 analysed samples, 100, 98·2, 72·3, 4·1 and 4·1% had coliform bacteria, faecal coliforms, E. coli, DEP and Salmonella, respectively. Identified DEP included enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC). The EPEC, ETEC and STEC were isolated each from 1·4% of samples. No E. coli O157:H7 were detected in any STEC-positive samples. The analysis of Kruskal-Wallis anova and median test of microbiological data showed that the microbiological quality of RECS did not differ between the different restaurants (P > 0·05).

Significance and impact of the study: This is the first report regarding microbiological quality and Salmonella, enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC) isolation from ready-to-eat cooked vegetable salads from Mexican restaurants. Ready-to-eat cooked vegetable salads could be an important factor contributing to the endemicity of EPEC, ETEC and STEC, and Salmonella caused gastroenteritis in Mexico.