Thesis Abstract

Abstract
Yoghurt is considered a popular dairy product consumed worldwide and is known for its nutritional benefits due to the presence of probiotic bacteria. However, the potential presence of harmful microorganisms in yoghurt raises concerns regarding food safety. This study aimed to assess the antimicrobial susceptibility pattern of microorganisms present in yoghurt samples obtained from different sources. A total of 50 yoghurt samples were collected from various local markets and supermarkets. The samples were cultured on selective media to isolate different microorganisms present in the yoghurt. The isolated microorganisms were identified using standard biochemical tests and confirmed through molecular techniques such as polymerase chain reaction (PCR). Antimicrobial susceptibility testing was performed using the disc diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. A panel of antibiotics representing different classes was chosen to test the susceptibility of the isolated microorganisms. The results were interpreted based on the zone of inhibition around the antibiotic discs. The findings revealed the presence of various microorganisms in the yoghurt samples, including Escherichia coli, Staphylococcus aureus, Lactobacillus species, and Streptococcus species. The antimicrobial susceptibility testing showed varying patterns of resistance among the isolated microorganisms. Escherichia coli exhibited resistance to multiple antibiotics, including ampicillin and ciprofloxacin, highlighting the potential risk of contamination in yoghurt products. Staphylococcus aureus isolates showed resistance to methicillin, indicating the presence of methicillin-resistant strains in the yoghurt samples. Lactobacillus species displayed susceptibility to most antibiotics tested, emphasizing their generally beneficial and probiotic nature. Streptococcus species exhibited intermediate resistance to some antibiotics, suggesting a moderate level of susceptibility. Overall, the study underscores the importance of monitoring and assessing the antimicrobial susceptibility pattern of microorganisms in yoghurt to ensure food safety and prevent potential health risks associated with contaminated dairy products. Continuous surveillance and quality control measures are essential to detect and mitigate antimicrobial resistance among foodborne pathogens, thereby safeguarding public health. Further research is warranted to investigate the sources and mechanisms of antimicrobial resistance in yoghurt microorganisms, contributing to the development of effective control strategies in the food industry.

Thesis Overview

1.0   INTRODUCTION

Yoghurt is a fermented dairy product obtained from the lactic acid fermentation of milk. It is one of the most popular fermented milk products in the world and produced commercially at home. (Willey et al., 2008). In its commercial production, non fat or low fat milk is pasteurized cooled to 43°c and are inoculated with known cultures of microorganisms referred to as starter cultures. The starter cultures may be a pure culture of a particular species of Lactobacillus or a mixed culture of Streptococcus thermophilus and Lactobacillus bulgaricus in a 1: 1 ratio. The coccus which is theStreptococcus thermophilus grows faster than the Rod which is the Lactobacillus bulgaricus and is primarily responsible for acid production while the rod adds flavor and aroma. The growth of these Microorganisms causes the transformation of milk’s sugar, lactose into lactic acid. This process gives yoghurt it’s texture. The associative growth of the two organisms results in acid production at a rate greater than that produced by them individually.

Yoghurt is generally made from a standardized mixture containing whole milk, partially defatted milk, condensed skim milk cream and non fat dry milk. Alternatively milk may be partly concentrated by removal of 15- 20% water in a vacuum pan or by heating. While the microorganisms fermenting milk confers on it certain health benefits inadequate pasteurized milk may contain microorganism of special importance to man. (Boor and Murphy, 2002).