Synthetic Culture Media Evaluated for the Detection of Coliform Bacteria in Milk, Cheese and Egg Melange

G Szita,L Soos,P Toth,N Solymos,S Bernáth,B Gyetvai,J Szita,M Gyenes,A Hajos

doi:10.2754/avb200877010143

Abstract

Simple synthetic culture media of liquid and solid form (X broth and X agar) were tested for selective isolation of coliform bacteria. Selectivity is based on the ability of coliform bacteria to grow when the minimal medium contains simple inorganic substances as nitrogen and carbon supply. Selectivity of the media was tested by inoculation of pure cultures of different microbes belonging to the genera of Staphylococcus, Bacillus and Pseudomonas and the family Enterobacteriaceae and was found to be complete in this range. The comparative investigation of milk, camembert cheese and egg melange samples in the traditional and new media proved good applicability of X broth and X agar for an effective and selective detection of coliform bacteria. When testing pasteurized milk samples, X agar detected coliforms in significantly higher counts than violet red-bile-lactose agar.

Highlights

In food microbiology qualitative and quantitative determination of indicator flora is a commonly used procedure which allows rapid conclusions concerning possible contamination of a product (Ingham and Schmidt 2000)
Selectivity is based on the ability of coliform bacteria to grow when the minimal medium contains simple inorganic substances as nitrogen and carbon supply
It was demonstrated that Escherichia coli could be grown in a minimal medium containing only an organic carbon source such as glucose, a nitrogen source such as (NH4)2SO4, and minerals (Jay 1996)

Summary

Introduction

In food microbiology qualitative and quantitative determination of indicator flora is a commonly used procedure which allows rapid conclusions concerning possible contamination of a product (Ingham and Schmidt 2000). A new simple selective and differentiating synthetic medium (X broth), which is easy to prepare, was developed in a liquid form for the selective cultivation of coliform bacteria from foodstuffs. This synthetic medium contains ammonium salt as a nitrogen source, lactose as a carbon source, and buffer salts but is free of inhibitors. The results of nationwide tests of coliform bacteria determination demonstrated that there was no difference in reproducibility, but the comparability was significantly better when the X broth was used. Applicability of the synthetic medium (X broth) for a detection of coliform bacteria was tested with good results by nationwide round tests on quick-frozen tomato paprika samples (Szita et al 2003).

Objectives

Methods

Results