Research – Evaluation of enumeration and MPN prediction methods for Staphylococcus aureus

Wiley Online

Abstract

Staphylococcal food poisoning is among the most prevalent causes of foodborne intoxication. To monitor the safety and quality of food, rapid and reliable enumeration procedures for Staphylococcus aureus are essential. Here, we assess culture‐based methods for the isolation and enumeration of S. aureus, testing different pre‐enrichment broths, plated media, and the automated TEMPO instrument. We evaluated enumeration of S. aureus in seven different food commodities, including two naturally contaminated foods, at levels ranging between 100 and 1,500 cfu/g of inoculated target and nontarget organisms. Sixty‐four food samples were analyzed. Duplicate test portions of 25 g each were homogenized with 225 ml of Butterfield’s phosphate buffer (1:10). Five tube most probable number (MPN) predictions comparing two pre‐enrichment broths, tryptic soy broth containing 10% NaCl and 1% sodium pyruvate (PTSBS) and modified Giolitti and Cantoni (GC) were assessed alongside the TEMPO STA card and the direct plate count method. The direct plate count method using Baird Parker agar and BP with Rabbit Plasma Fibrinogen versus TEMPO STA demonstrated the highest proportion of agreement at 89.19%. The two different pre‐enrichment broths assessed, PTSBS versus GC exhibited the lowest proportion of agreement at 47.5%. The TEMPO STA yielded results in 24 hr versus the current 4‐day PTSBS MPN method for S. aureus, with an 84.62% agreement.

Practical applications

Overall food quality, recalls, and other regulatory decisions are often contingent upon enumeration results. A prompt turnaround time can assist in expediting the release of unadulterated foods, and the swift removal of adulterated foods out of the food supply chain. This is paramount to the microbiology and food safety community who must consider which methods will provide more accurate and timely assessments of food contamination.

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