The Combined Effect of pH and Temperature on the Survival of Salmonella enterica Serovar Typhimurium and Implications for the Preparation of Raw Egg Mayonnaise.

Thilini Piushani Keerthirathne,Harriet Whiley,Howard Fallowfield,Kirstin Ross

doi:10.3390/pathogens8040218

Abstract

Raw egg products are often associated with salmonellosis. The Australian guidelines recommend raw egg mayonnaise to be prepared and stored under 5 °C and adjusted to a pH less than 4.6 or 4.2. Despite these guidelines, a significant amount of salmonellosis outbreaks are recorded annually in Australia. The aim of this study was to investigate the effect of pH and temperature on the survival of Salmonella Typhimurium (ST) in peptone water (PW) and mayonnaise. The pH of PW and mayonnaise was adjusted to 4.2, 4.4 and 4.6 using acetic acid and vinegar, respectively. The PW and mayonnaise were inoculated with ST and incubated at 37 °C, 23 °C, and 4 °C. The survival of Salmonella was determined using the drop plate method. Survival was significantly (p < 0.05) improved at 4 °C. In both mayonnaise and PW, following 24 h, there was no ST growth at pH 4.2. Resuscitation of ST was rapidly observed at 4 °C while complete inactivation was observed at 37 °C at pH 4.2, 4.4, and 4.6 in both PW and mayonnaise. Lower temperatures protected ST from the bactericidal effect of low pH. “The preparation of mayonnaise at pH 4.2 or less and incubating it at room temperature for at least 24 h could reduce the incidence of salmonellosis”.

Highlights

IntroductionIn Australia, the incidence of salmonellosis has been increasing over the last decade [2] with the primary source of outbreaks identified as raw eggs and raw egg products [3,4]
Nontyphoidal salmonellosis is a gastrointestinal foodborne illness affecting public health [1].In Australia, the incidence of salmonellosis has been increasing over the last decade [2] with the primary source of outbreaks identified as raw eggs and raw egg products [3,4]
On-site manufactured mayonnaise has been linked with several salmonellosis outbreaks [13,14] and is a growing public health concern as it is often prepared in cafes and restaurants

Summary

Introduction

In Australia, the incidence of salmonellosis has been increasing over the last decade [2] with the primary source of outbreaks identified as raw eggs and raw egg products [3,4]. South Australia, from March 2017 to July 2018, salmonellosis outbreaks were predominantly recorded due to eggs and raw egg products [6]. Smittle [12] states that as factory-made mayonnaise is produced using pasteurized eggs, it isn’t a threat to public health. On-site manufactured mayonnaise has been linked with several salmonellosis outbreaks [13,14] and is a growing public health concern as it is often prepared in cafes and restaurants

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