Presence and growth prediction of Staphylococcus spp. and Staphylococcus aureus in Minas Frescal cheese, a soft fresh cheese produced in Brazil.

Abstract

Physical-chemical characteristics of Minas Frescal cheese (MFC) favor the growth of Staphylococcus spp. and allow the production of enterotoxins by specific strains. Here, we aimed to characterize the physical-chemical aspects (pH, storage temperature, and salt content) and the presence of Staphylococcus spp. in MFC samples (n = 50) to support a modeling study for the growth by this microorganism. Coagulase-positive staphylococci isolates were obtained and subjected to PCR assays to identify them as Staphylococcus aureus (nuc) and to detect staphylococcal enterotoxin-related genes (sea, seb, sec, sed, see). Staphylococcus aureus growth kinetics (maximum growth rate, Grmax, and lag time) were predicted based on ComBase model and MFC physical-chemical aspects. Mean counts of Staphylococcus spp. ranged from 3.3 to 6.7 log cfu/g, indicating poor hygiene practices during production. Selected isolates (n = 10) were identified as S. aureus, but none presented classical enterotoxin-related genes. pH, temperature, and salt content ranged from 5.80 to 6.62, 5°C to 12°C, and 0.85% to 1.70%, respectively. The Grmax values ranged from 0.012 to 0.419 log cfu/g per h. Independent of the storage temperature, the lowest Grmax values (0.012 to 0.372 log cfu/h) were obtained at pH 5.80 associated with salt content of 1.7%; independent of the pH and salt content, the best temperature to avoid staphylococcal growth was 7.5°C. Hygienic conditions during MFC production must be adopted to avoid staphylococcal contamination, and storage at temperatures lower than 7.5°C can prevent staphylococcal growth and the potential production of enterotoxins.