Detection of Salmonella Species in Mexican-style Cheese with PCR-based Technology

Introduction: Mexican-style cheese is a group of perishable products that can be a vehicle of human pathogens such as Salmonella spp. Detection time of pathogens in this food type is crucial because of its short shelf life. Some commercial PCR-based technology provides a protocol for qualitative detection of Salmonella in approximately 26 hours as an alternative to the traditional method.

Purpose: The purpose of the study was to evaluate the detection limits for Salmonella spp. using a PCR-based technology in Mexican-style cheeses.

Methods: Salmonella Montevideo (ATCC 8387) resistant to rifampicin was inoculated in two types of Mexican-style cheese (panela and oaxaca cheese; 25 g portions) with 4, 28 and 68 cells. Pathogen detection was performed according to the ANSR protocol and traditional methodology. At the end of enrichment, Salmonella was quantified on tryptic soy agar supplemented with rifampicin. Assays were performed in triplicate.

Results: Salmonella was detected in the inoculated cheese samples in all cases. The concentration of Salmonella after enrichment was 8 log CFU/ml in oaxaca cheese and 6 log CFU/ml in panela cheese. Total plate count of oaxaca and panela cheese were 6.3 and 8.9 log CFU/g, respectively. Associated microbiota in panela cheese could be hindering Salmonella growth; however, ANSR technology was able to detect it.

Significance: PCR-based technology was able to detect Salmonella in panela and oaxaca cheese, offering a reliable alternative to traditional methodology.