**3. Pathogenic** *Staphylococcus aureus* **transmitted through rice**

### **3.1 Characteristics and diseases caused by** *Staphylococcus aureus*

*Staphylococcus aureus* is one of the bacteria that cause food poisoning. *Staphylococcus aureus* is commonly found in the environment (soil, water, and air) and located on humans' nose and skin. *Staphylococcus aureus* is a spherical, Gram-positive, non-spore bacteria. The genus Staphylococcus divided into 32 species and subspecies. *Staphylococcus aureus* causes food poisoning by producing Staphylococcal Enterotoxin (SE) [39, 40].

*Staphylococcus aureus*'s growth and survival depend on several environmental factors such as temperature, water activity (aw), pH, presence of oxygen, and food composition. These physical growth parameters varied for different strains of *Staphylococcus aureus* [41]. The temperature range for *Staphylococcus aureus* growth is 7–48°C, with an optimum temperature of 37°C. *Staphylococcus aureus* is resistant to freezing and does well in foods stored below −20°C; however, viability is reduced at −10 to 0°C. *Staphylococcus aureus* easily killed during pasteurization or cooking. *Staphylococcus aureus* growth occurs in the pH range 4.0–10.0, with an optimum of 6–7 [41].

*Staphylococcus aureus* is a facultative anaerobe so it can grow in both aerobic and anaerobic conditions. However, growth occurs at a much slower rate under anaerobic conditions [41]. For non-sporing mesophilic bacteria, *Staphylococcus aureus* has relatively high heat resistance [41]. A highly heat resistant *Staphylococcus aureus* strain (D-value at 60°C > 15 min in broth) has identified from foodborne outbreaks in India [42].

Several chemical preservatives, including sorbate and benzoate, inhibit the growth of *Staphylococcus aureus*. The effectiveness of this preservative increases as the pH decreases. Methyl and propyl parabens are also useful [41, 43].

Symptoms of staphylococcal food poisoning generally have a rapid onset, appearing approximately 3 h after ingestion (range 1–6 h). Common symptoms include nausea, vomiting, stomach cramps, and diarrhea. The individual may not show all the signs associated with the disease. In severe cases, headaches, muscle cramps, and temporary changes in blood pressure and pulse may occur. Recovery is usually between 1 and 3 days [39, 41]. Death is rare (0.03% for the general population) but occasionally reported in children and the elderly (death rate 4.4%) [40]. *Staphylococcus aureus* can cause various health problems not related to food such as skin inflammation (e.g., ulcers and style), mastitis, respiratory tract infections, wound sepsis, and toxic shock syndrome [40, 41].

Staphylococcal food poisoning caused by the ingestion of foods containing pre-formed SE [44], there are several types of SE; enterotoxin A is most commonly associated with staphylococcal food poisoning. Enterotoxins D, E, and H, and to a lesser extent B, G, and I have also associated with staphylococcal food poisoning [45, 46].

SE produced during the exponential phase of *Staphylococcus aureus* growth in a strain-dependent quantity. Typically, the disease-inducing dose of SE occurs when at least 105–108 CFU/g of *Staphylococcus aureus* are present [45, 40]. Most of the genes for SE located in plasmid or prophage elements. Thus, transfer between strains can occur, modifying the ability of *Staphylococcus aureus* strains to cause disease and contributing to pathogen evolution [44, 46].

As the temperature decreases, the SE production rate also decreases. However, SE remained stable under frozen storage. SE is highly resistant to heating and can withstand the processes used to sterilize low-acid canned foods. SE production can occur in the pH range 4.5–9.6, with an optimum of 7–8. SE production can occur in anaerobic and aerobic environments; however, toxin production is optimal under aerobic conditions [41].
