Frequency and Correlation of Some Enteric Indicator Bacteria and Salmonella in Ready‐to‐Eat Raw Vegetable Salads from Mexican Restaurants

Abstract

Data about Salmonella presence in ready-to-eat raw vegetable salads (REVS) consumed in restaurants or sold as REVS in México is not available. The objective of the study was to measure the frequency of coliform bacteria (CB), fecal coliform (FC), Escherichia coli, and Salmonella in REVS from different types of restaurants and determine the correlations of CB, FC, and E. coli versus Salmonella from frequencies and concentration data. The REVS were purchased from 3 types of restaurants: national chain restaurants (A1 , A2 ); local restaurants (B1 , B2 ); and small restaurants in local markets (C1 , C2 , C3 ). Two restaurants for each A and B, and 3 for C, were included. Forty REVS were purchased at each A and B restaurant, and 20 at each C restaurant. CB were tested by plate count using violet red bile agar, FC and E. coli were detected by the most probable number method and E. coli confirmed using IMViC test; conventional method of culture was used for Salmonella. Of 220 analyzed samples, 100% had CB, 95.5% had FC, 83.2% had E. coli, and 6.8% had Salmonella. E. coli frequency was equal to or exceeded 75% in all the cases: 75% (A1 , C1 , C2 ), 80% (B2 ), 85% (B1 , C3 ), and 100% (A2 ). Salmonella frequency was equal to or exceeded 2.5% in all cases: 2.5% (A1 ), 5% (B2 , C2 ), 7.5% (B1 ), and 10% (A2 , C1 , C3 ). No correlation was observed between FC or E. coli versus Salmonella in the analyzed salads. All the tested salads were of poor quality microbiologically, and microbiological quality did not differ between the restaurants types.