Salmonella Lab Report

1 INTRODUCTION

1.1 Objectives

To learn, understand and perform method of isolating and enumerating Salmonella spp. in a food sample.

1.2 Hypothesis

To achieve a negative results in food sample with the absence of Salmonella spp.

1.3 Introduction

The genus Salmonella belong in the family of Enterobacteriaceae is a group of rod-shaped, Gram-negative, and facultative anaerobic bacteria, which grow with or without oxygen. It is also a non-spore forming and a motile or non-motile bacterium with exception of S.gallinarum and S.pullorum. The genus Salmonella consist of two species, S. enterica, and S. bongori. Salmonella enterica is subdivided into six subspecies and over 2,500 serovars or serotypes characterised based on the distinct

Yeast extract in the agar supply sources of nitrogen, carbon, and vitamin for the metabolism of organisms. Xylose, Lactose, and Sucrose acts as the fermentable carbohydrate sources. Sodium Deoxycholate acts as the selective agent while Sodium Chloride provides buffering capacity. Phenol red is used as the indicator. The selective agents in the agar such as Sodium Thiosulfate and Ferric Ammonium Citrate support visualization of hydrogen sulfide production under alkaline conditions. The release of hydrogen sulfide is from the fermentation of xylose by Salmonella hence resulting in red colonies with black centres. Black centre in the colony is resulted from the reaction with iron salts (III). Non-Hydrogen sulfide Salmonella will produce only red colony. [9],

This agar comprise of dextrose, lactose and sucrose, which acts as the carbohydrates sources. The medium osmotic balance is maintain by Sodium chloride The fermentation of the carbohydrate lead to acid production of yellow colour agar, detected by the pH indicator in the media, phenol red. Detection of hydrogen sulfide is through the indicator Ferric Ammonium citrate. A black colour will be seen in the medium from the hydrogen sulfide production from thiosuplhate due to FeS production. [9],