Characteristics of Staphylococcus aureus Isolated from a Case of Foodborne Outbreak in Bulgaria

Abstract This paper presents an outbreak provoked by methicillin-resistant strains of coagulase-positive S. aureus (CPS), produced staphylococcal enterotoxins (se) in pig meatballs and potato salad consumed from 70 people in the village Mamarchevo, Bulgaria. Eighteen women aged 50 to 70 years, and two children aged 4 and 5 years have demonstrated a severe malaise with vomiting and indigestion. Two food samples and isolates of CPS were received in the laboratory of Bulgarian Food Safety Agency. Both samples were found to have a high level of CPS. The level of S. aureus contamination in the potato salad was 8.3 logs CFU/g and 7.7 logs CFU/g in roasted meatballs, which was a significant reason to doubt the production of the toxin. The samples were analyzed according to the European Screening Method v5 using mini VIDAS SET2. The results showed a presence of staphylococcal enterotoxin (TV 2.67 for meatballs and TV 3.27 for potato salad), which was the reason for the ensuing food intoxication. EURL CPS applying quantitative indirect sandwich-type ELISA confirmed the presence of sea, sec and sed in the potato salad and sea and sed in the roasted meatballs. Two CPS isolates were confirmed as S. aureus by a species-specific 23S rRNA targeted PCR test. Real-time PCR method detected sea, sed, seg, sei, sej, and ser genes in S. aureus strains, found in both matrixes. Multiplex PCR method proved the existence of the mecA gene in both S. aureus strains. Resistance to cefoxitin (>16 mg/L), penicillin (>2 mg/L), kanamycin (64 mg/L) and sulfamethoxazole (>512 mg/L) was found.