Prevalence and virulence genes of Staphylococcus aureus from food contact surfaces in Thai restaurants

Background

Staphylococcus aureus is one of the most common pathogens responsible for food poisoning due to its ability to produce staphylococcal enterotoxin (SE). S. aureus can form biofilms on the surfaces of food processing devices, enabling the distribution of SE on foods through cross-contamination events. Thailand is known for its exotic cuisine, but there is no data on the prevalence of SE-harboring S. aureus in restaurants in Thailand.

Methods

In this study, we conducted surface swabs on surfaces of kitchen utensil that come into contact with food and on the hands of food handlers working in restaurants in the north part of Thailand. Isolated S. aureus was investigated for biofilm formation, virulence, and SE genes.

Results

Two hundred S. aureus were isolated from 650 samples. The highest prevalence of S. aureus contamination was detected on the hands of food handlers (78%), followed by chopping boards (26%), plates (23%), knives (16%), spoons (13%), and glasses (5%). All of them were methicillin-sensitive S. aureus (MSSA) and the mecA gene was not present in any strains. Biofilm formation was detected using the CRA method, and 49 (24.5%) were identified as biofilm-producing strains, with the hands of food handlers identified as the primary source of biofilm-producing strains. The prevelence of biofilm-related adhesion genes detected were: icaAD (13%), fnbA (14.5%), cna (6.5%), and bap (0.5%). Two classical enterotoxin genes, sec and sed, were also found in four and six of the S. aureus isolates, respectively, from hands and utensils.

Conclusion

The highest prevelence of S. aureus was detected on the hands of food handlers. S. aureus strains with biofilm and enterotoxin production abilities were discovered on food contact surfaces and the hands of food handlers, implying significant risk of food contamination from these sources that could be harmful to consumers. To avoid cross-contamination of food with food contact items, the food handlers' hands should be properly washed, and all food preparation equipment should be thoroughly cleaned.

Desiccation tolerance in Staphylococcus aureus

Staphylococcus aureus is a multidrug-resistant pathogen that not only causes a diverse array of human diseases, but also is able to survive in potentially dry and stressful environments, such as the human nose, on skin and on inanimate surfaces such as clothing and surfaces. This study investigated parameters governing desiccation tolerance of S. aureus and identified several components involved in the process. Initially, the role of environmental parameters such as temperature, growth phase, cell density, desiccation time and protectants in desiccation tolerance were determined. This established a robust model of desiccation tolerance in which S. aureus has the ability to survive on dry plastic surfaces for more than 1,097 days. Using a combination of a random screen and defined mutants, clpX, sigB and yjbH were identified as being required for desiccation tolerance. ClpX is a part of the ATP-dependent ClpXP protease, important for protein turnover, and YjbH has a proposed linked function. SigB is an accessory sigma factor with a role in generalized stress resistance. Understanding the molecular mechanisms that govern desiccation tolerance may determine the break points to be exploited to prevent the spread of this dangerous pathogen in hospitals and communities.