Expression of toxic shock syndrome toxin-1 gene of Staphylococcus aureus in milk: Proof of concept

Abstract

The aim of this study was to assess the expression of a toxic shock syndrome toxin-1 (TSST-1) gene of Staphylococcus aureus in different types of milk, depending on inadequate temperature and storage conditions. Pasteurized and UHT milk were inoculated with monotoxic TSST-1 strain of S. aureus and growth kinetics was determined by the drop plate method using Baird-Parker agar medium in accordance with EN ISO 6888-1. The patterns of gene regulation were detected by quantitative reverse transcriptase PCR. Relative quantification method for statistical significance testing was used to detect significant gene expression responses. The results of experiments showed the dependence of the growth rate and consequent up-regulation of TSST-1 encoding gene on storage time-temperature and type of milk. In contaminated pasteurized and UHT milk kept at both 15 °C and 22 °C S. aureus significantly increased its virulent potential over time. This effect was a bit more emphasized in UHT milk serving as a "proof of concept". Possible explanation could be a presence of lactic acid bacteria in pasteurized milk which is known to have down-regulatory effect on TSST-1 gene. Maintenance of the milk storage temperature below 8 °C and employment of microbiological control measures in hygienic practices, from milk producer through retailer and on to the consumer is of utmost importance to decrease risk of non-emetic staphylococcal poisoning.

Staphylococcus aureus Exotoxins and Their Detection in the Dairy Industry and Mastitis

“…These enterotoxins are mainly found in foods with high amounts of starch and protein, such as meat products, eggs, and dairy products [35,36]; but enterotoxin production is also affected by other factors, such as pH, water activity, temperature. The SEA, SEB, SEC, SED, and SEE classic enterotoxins are responsible for 95% of SFP; with SEA and SED as the most common causes of food poisoning, due to their stability under a wide range of water activities and pH conditions [34,37]. Recent published papers identified additional SEs (SEG, SEH, SEI, SER, SES, SEIY, and SET) as putative food poisoning agents.…”

“…As is the case for SAg, TSS-1 activates T cells by increasing immunological activity. The presence of TSS-1, in either humans, animals, or food, is associated with food poisoning, but its prevalence is not yet as well-known as SEs [37]. The TSST-1 toxin load has been studied in different types of milk under different storage conditions (pasteurized and UHT milks treated at 15 and 22 • C), as well as following inoculation with different amounts of S. aureus.…”

“…Staphylococcal SEB can be inactivated by pepsin digestion, at pH 2.0, although it is pepsin-resistant at higher pH values [39]. TSST-1 is stable under a variety of negative conditions, such as heat treatment, pepsin and trypsin digestion; in fact, it retains its superantigen activity even when degraded to smaller peptides [37].…”

Review on anti-microbial resistance patterns of staphylococcus aureus isolated from mastitic cow’s milk: Ethiopian context

“…Foods contaminated with toxins or viable S. aureus cells are directly linked to inadequate sanitation practices. Although hazardous bacteria are frequently removed from human food, many poisons remain stable after heat treatment, especially when done over long periods (Babic et al, 2018).…”

Cell-Free Culture Supernatants of Lactobacilli Modify the Expression of Virulence Factors Genes in Staphylococcus aureus

“…Staphylococcus aureus produces different toxins and enzymes including enterotoxins, DNase, coagulase, lipase, TSST-1 (tst), and hemolysin involved in the pathogenesis of the diseases (3). The enterotoxins (sea to see and seg to sej) are heat-resistant (4,5). These toxins can cause food poisoning, staphylococcal gastroenteritis, and diverse autoimmune and allergic diseases (6,7).…”