Author: Thilini Keerthirathne
Keerthirathne, Thilini, 2020 Potential control mechanisms for Salmonella enterica serovar Typhimurium contamination of eggs and raw egg products, Flinders University, College of Science and Engineering
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Salmonellosis is a foodborne gastrointestinal illness caused by Salmonella, with outbreaks in Australia commonly linked to eggs and raw egg products. Globally, S. Enteritidis is the primary cause of salmonellosis outbreaks linked to eggs and raw egg products; however, in Australia S. Typhimurium is the strain most frequently identified. Previous research has focused on the control of S. Enteritidis; however, there is a need for more research investigating potential control mechanisms for S. Typhimurium to inform Australian food safety guidelines and public health interventions. This research project focused on, the risk factors associated with keeping chickens in the backyards and the role this may play in the spread of salmonellosis and exploring control mechanisms for S. Typhimurium in eggs and raw egg products.
Keeping poultry in domestic backyards is increasing in popularity. This could potentially increase the spread of zoonotic bacterial species such as Salmonella, Campylobacter and Shigella as these bacterial species are often isolated from poultry and poultry products. In this study, chicken faeces were collected from 82 backyards and 15% were either positive for Salmonella or Campylobacter but none were positive for Shigella. Following the questionnaires collected from the backyard chicken owners, washing dirt off eggs, storing the eggs at room temperature, consumption of raw egg products, spreading poultry faeces in the backyard and having flocks with more than 10 birds were identified as risky behavioural patterns. This demonstrates the need for better education as these risk factors could increase the likelihood of foodborne diseases linked to pathogens present in the backyard chicken flocks.
Temperature and pH are commonly used to control replication and survival of pathogenic bacteria in food. The Food Standards Australia New Zealand (FSANZ) recommends the preparation, processing, transporting and storage of raw egg products such as mayonnaise to be conducted under a temperature less than 5oC. The guidelines further state that the pH of the mayonnaise should be adjusted to less than 4.6 or 4.2. Despite these guidelines salmonellosis outbreaks have increased during the past decade in Australia. This was the first study to focus on exploring the survival of S. Typhimurium in raw egg mayonnaise, with the aim of informing Australian food safety guidelines. The results of this research contradict the current guidelines, as a higher survival rate of S. Typhimurium was observed at 4oC. The findings from this research suggested that storing mayonnaise (pH adjusted to 4.2) at room temperature for at least 24 h prior to consumption could reduce the incidence of salmonellosis linked to eggs and raw egg products in Australia.
In order to reduce the incidence of salmonellosis outbreaks related to eggs and raw egg products, the current food safety guidelines should be revised and modified according to the novel scientific data. The guidelines involving the preparation of raw egg products should be amended to inform the environmental health officers (EHOs), chefs and food handlers to leave the pH adjusted (pH 4.2) mayonnaise at room temperature for at least 24 h before consumption. Adaptation of the developed decontamination method prior to the preparation of raw egg products will reduce cross contamination in the kitchen and further ensure food safety.
Foodborne illnesses often occur due to inappropriate food handling. Competent policy modification and effective policy implementation along with educational programmes for the general public, EHOs, chefs and food handlers could reduce the public health burden of gastrointestinal diseases linked to eggs and raw egg products in Australia.
Keywords: salmonellosis, pasteurization, egg quality, mayonnaise, food handler, chef, food safety, sous-vide, resuscitation; mayonnaise; salmonellosis; gastroenteritis; public health; chicken eggs
Subject: Biology thesis
Thesis type: Doctor of Philosophy
Completed: 2020
School: College of Science and Engineering
Supervisor: Harriet Whiley