Miniaturized most probable number for the enumeration of Salmonella sp in artificially contaminated chicken meat

Fl Colla,El Dickel,Lr Dos Santos,L Parizotto,F Pilotto,Vp Do Nascimento,L Mion,Lb Rodrigues

doi:10.1590/s1516-635x2014000100006

Abstract

Salmonella is traditionally identified by conventional microbiological tests, but the enumeration of this bacterium is not used on a routine basis. Methods such as the most probable number (MPN), which utilize an array of multiple tubes, are time-consuming and expensive, whereas miniaturized most probable number (mMPN) methods, which use microplates, can be adapted for the enumeration of bacteria, saving up time and materials. The aim of the present paper is to assess two mMPN methods for the enumeration of Salmonella sp in artificially-contaminated chicken meat samples. Microplates containing 24 wells (method A) and 96 wells (method B), both with peptone water as pre-enrichment medium and modified semi-solid Rappaport-Vassiliadis (MSRV) as selective enrichment medium, were used. The meat matrix consisted of 25g of autoclaved ground chicken breast contaminated with dilutions of up to 106 of Salmonella Typhimurium (ST) and Escherichia coli (EC). In method A, the dilution 10-5 of Salmonella Typhimurium corresponded to >57 MPN/mL and the dilution 10-6 was equal to 30 MPN/mL. There was a correlation between the counts used for the artificial contamination of the samples and those recovered by mMPN, indicating that the method A was sensitive for the enumeration of different levels of contamination of the meat matrix. In method B, there was no correlation between the inoculated dilutions and the mMPN results.

Highlights

Bacteria of the genus Salmonella play a major role in poultry farming
In method A, the dilution 10-5 of Salmonella Typhimurium corresponded to >57 most probable number (MPN)/mL and the dilution 10-6 was equal to 30 MPN/mL
There was a correlation between the counts used for the artificial contamination of the samples and those recovered by miniaturized most probable number (mMPN), indicating that the method was sensitive for the identification of different levels of contamination of the meat matrix

Summary

Introduction

Bacteria of the genus Salmonella play a major role in poultry farming. Avian-adapted serovars cause gastroenteritis, septicemia and eventually impair productivity, while human-adapted typhoidal serovars cause gastroenteritis and are major barriers for the exports of poultry products. The identification of Salmonella in products of animal origin by qualitative methods (conventional microbiological tests) is widely acknowledged, but the enumeration of this microorganism is not used on a routine basis (Borowsky et al, 2005). Enumeration at the poultry farm level up to processing is crucial to estimate the extent of contamination of meat cuts and carcasses and to assess the efficacy of Good Manufacturing Practices (GMP) and Hazard Analysis and Critical Control Points (HACCP) used for the control of pathogens (Borsoi et al, 2010)

Objectives

Methods

Results