Characterization of Enterotoxin Genes and Antibiotic Resistance Patterns in Staphylococcus aureus Blood Culture Isolates

Background: Staphylococcus aureus is an opportunistic pathogen that can result in skin infections, respiratory infections, sinusitis, and food poisoning. Methicillin-resistant Staphylococcus aureus (MRSA), due to antibiotic resistance, is a major determinant of healthcare-associated infections. Although the resistance mechanisms of MRSA have been reported to be related to exotoxins, research on this subject remains limited. This study aimed to examine the relationship between MRSA isolated from blood cultures and Staphylococcal enterotoxin (SE) genes. Methods: A total of 135 S. aureus clinical isolates were collected from blood cultures, including 99 MRSA and 36 methicillin-susceptible Staphylococcus aureus (MSSA). The eight SE genes, including sea, seb, sec, sed, see, seg, seh, and sei, were compared between MRSA and MSSA using quantitative PCR (qPCR) SYBR Green assay. Results: Detection rates of sec, seg, and sei genes were significantly different (p < 0.001) between MRSA and MSSA. Among the 99 MRSA isolates, 88 (88.9%) harbored two or more SE genes, of which 43 (43.4%) isolates carried both seg and sei genes. The multi-positive SE gene profiles, which have more than three genes, accounted for 40 (40.4%) isolates, of which 38 (38.4%) harbored the sec, seg, and sei genes. The MRSA group carried more diverse SE gene profiles than the MSSA group and demonstrated significant differences in positivity rates, such as the sec, seg, and sei genes. Conclusions: In this study, the presence of the SE genes in clinical isolates was determined using a molecular diagnostic method. Among the SE genes, the sec, seg, and sei genes showed significant differences compared with the MSSA group due to the high positivity rate in the MRSA group. Moreover, most of the genes were found in combination with other SE genes. Our findings demonstrate distinct distribution profiles of SE genes between MRSA and MSSA isolates, highlighting the need for continuous molecular monitoring. These results will provide an important indicator for research on MRSA resistance and effective infection control.