Purpose: To test resistance of SRSS and non-SRSS and of Pediococcus faecium as potential surrogate, to desiccation, irradiation and dry storage in talcum powder as dry-inoculation vehicle for spices.
Methods: Talcum powder was inoculated with cocktails containing approx. 10 log CFU/ml of: 1) Salmonella enterica ser. Rissen SAL1449 and Montevideo SAL4599 (RM), 2) S. enterica ser. Choleraeasuis ATCC-13312, Enteritidis ATCC-4931, Newport ATCC-6962, and Typhimurium ATCC-700720 (MP15), or 3) Pediococcus faecium NRRL B-2354 (PF). These inoculated talc batches were dried at 35°C until reaching 0.45 aw. The desiccation effect was determined by counting surviving Salmonella and PF. Sample dilutions were surface-spread onto TSA, incubating at 35°C for 3 h and then overlaid with XLT4 or KFS to recover stressed bacteria, continuing incubation for 24 h. Inoculated talc sets were gamma-irradiated and D10-values were calculated. Survivability was determined by storing the talc at 25, 4, and -18°C, determining bacterial populations at intervals during 15 weeks.
Results: Counts of RM and MP15 were reduced by 2.1 and 3.4 log cycles, respectively, during talcum drying (P<0.05), whereas PF was reduced 0.1 log. RM, MP15 and PF showed no significant differences over the 15-week dry storage at -18, 4 and 25°C (P<0.05). D10-values for RM and MP15 were 0.673 and 0.623 kGy, respectively, (P>0.05), whereas for PF was 0.743 kGy (P>0.05).
Significance: Salmonella strains isolated from spice-related outbreaks survived dehydration better than non-spice-related strains during inoculum preparation. PF was more resistant than Salmonella to dehydration, irradiation and storage in dry conditions, supporting its potential use as surrogate.