Characterization of enterotoxin A-producing <em>Staphylococcus aureus</em>

Abstract

PurposeThis study aims to characterize the wild-type staphylococcal enterotoxin A (SEA)-producing Staphylococcus aureus.Materials and methodsWe identified 29 wild-type sea-positive S. aureus isolates from dairy and meat samples, as well as from patients, measured the amount of SEA produced under favorable cultivation conditions using enzyme-linked immunosorbent assay and sea mRNA transcriptional level and investigated the phage type as well as genetic diversity by means of pulsed-field gel electrophoresis and multilocus sequence typing.ResultsAmong 29 sea-positive isolates, 22 were from food sources (including one outbreak case) and seven from clinical patients. Five enterotoxin gene profiles, namely, sea (14 isolates), sea+sec (9 isolates), sea+seb (4 isolates), sea+seb+sec (1 isolate) and sea+seb+sed (1 isolate), were identified. Multilocus sequence typing generated sequence type (ST)1 (13 isolates), ST6 (5 isolates), ST59 (3 isolates), ST239 (3 isolates), ST5 (2 isolates), ST188 (2 isolate) and ST15 (1 isolate). The amount of SEA per 108 colony-forming unit (CFU) after 24 h of incubation was 1.1–33.5 (mean, 8.74; SD, 7.7) ng/108 CFU. The amount of SEA per hour incubation in the log growth phase was 0.1–12.0 (mean, 2.37; SD, 3.06) ng/108 CFU. Overall, 54.2% of SEA was produced in the log growth phase. Both the transcriptional level of sea mRNA and the amount of SEA in the log growth phase correlated well with the amount of SEA after 24 h of cultivation. Four isolates, namely, SA-212, SA-217, SA-340 and SA-341, were categorized to be of high SEA production (877–1,109 ng/mL, 24 h). The total amount of SEA was mainly based on the amount of SEA in 108 CFU, not the relatively fixed bacterial cell counts (21.1–43×108 CFU/mL). Seven isolates from patients all carried the ФMu3A phage, whereas 21 of the 22 isolates from the environmental sources all carried the ФSa3ms phage.ConclusionThe present study exhibits varied SEA production capacity of the wild sea-positive S. aureus strains. An apparent boundary in phage types between strains from the clinical samples and strains from the environment was also identified.

Multiple antibiotic resistance and virulence factors of Staphylococcus aureus strains isolated from dairy farms in South Sulawesi, Indonesia

“…In contrast, previous findings have reported the presence of the sea in human isolates (Saadati et al 2011). The sea gene is the most commonly associated source of foodborne poisoning in humans due to improper handling and storage (Chen et al 2018) and cases of subclinical mastitis in cattle (Fursova et al 2018). The toxic shock syndrome toxin-1 (TSST-1), which is encoded by the tst gene, is a significant virulence factor in S. aureus infections which can trigger excessive and nonconventional T-cell activation and cytokines release and consequently interfere with the immune system function systemically (Zhao et al 2019).…”

Evaluation of the Antimicrobial Activity of ZnO Nanoparticles against Enterotoxigenic Staphylococcus aureus

“…To ensure the reliability of results, three replicate measurements were acquired. The test was carried out according to the manufacturer’s recommendations [ 32 ].…”