Rapid colorimetric loop-mediated isothermal amplification for hypersensitive point-of-care Staphylococcus aureus enterotoxin A gene detection in milk and pork products

Srimongkol, Grittaya; Ditmangklo, Boonsong; Choopara, Ilada; Thaniyavarn, Jiraporn; Dean, Deborah; Kokpol, Sirirat; Vilaivan, Tirayut; Somboonna, Naraporn

Staphylococcus aureus strains carrying enterotoxin A gene (sea) causes food poisoning and cannot be distinguished from non-pathogenic strains by the culture method. Here, we developed a rapid, specific and sensitive visual detection of sea using loop-mediated isothermal amplification (LAMP) combined with nanogold probe (AuNP) or styryl dye (STR). LAMP-AuNP and LAMP-STR can detect as low as 9.7 fg (3.2 sea copies) and 7.2 sea copies, respectively, which were lower than PCR (97 fg or 32 sea copies). The excellent performance of these new assays was demonstrated in food samples using crude DNA lysates. While the culture method detected 10(4) CFU/g in ground pork and 10 CFU/mL in milk in 5–7 days, LAMP-AuNP could detect down to 10 CFU/g for both samples in 27 minutes. Analyzing 80 pork and milk samples revealed that the LAMP-AuNP showed 100% sensitivity, 97–100% specificity and 97.5–100% accuracy, which were superior to the culture method, and comparable to PCR but without requirement of a thermal cycler. Furthermore, our LAMP-AuNP detect sea at a range below the food safety control (<100 CFU/g). The LAMP-STR quantitated sea in 10–1,000 CFU (7.2–720 copies). Our crude DNA lysis combined with LAMP-AuNP/STR present effective point-of-care detection and facilitate appropriate control strategies.