Comparative Study of Recovery of Salmonella javiana from Mozzarella Cheese by Two Official Analytical Procedures

The Association of Official Analytical Chemists (AOAC) and the Canadian Health Protection Branch (CHPB) methods for detection of Salmonella spp. were compared for recovery of Salmonella javiana from experimentally contaminated mozzarella cheese. Ten trials were conducted with two levels of random surface contamination of cheese. Five samples per level of contamination were randomly chosen and analyzed by each method. The results showed that there was no significant difference between the two methods (P < 0.05). When S. javiana was directly added to shredded cheese and analyzed immediately, the recovery was identical with both methods; 7 of 10 samples were positive by each method. However, when the directly contaminated cheese was stored for 7 days and analyzed by both methods, the results differed. The AOAC method showed only 3 positive samples, whereas the CHPB yielded 6, compared to 7 positive samples before storage by both methods. During preenrichment the pH decreased to a greater extent with the AOAC method (7.4 to 4.4) than with the CHPB method (7.6 to 5.7) in 24 h; this pH decrease resulted in 1 log higher number of S. javiana counts in the latter (10⁶ CFU/ml and 10⁷ ml).