Survival of salmonella on red meat in response to dry heat

Abstract

Red meat is associated with Salmonella outbreaks, resulting in negative impacts for the processing industry. Little work has been reported on the use of dry heat as opposed to moist heat against Salmonella on red meat. We determined the effect of drying at 258C and dry heat at 708C with ~10% relative humidity for 1 h against 11 Salmonella strains of multiple serovars on beef, lamb, and goat and rubber as an inert surface. Each strain at ~108 CFU/mL was inoculated (100 μL) onto 61 g (1 cm2) of each surface and allowed to attach for 15 min in a microcentrifuge tube. Samples were then exposed to 70 and 258C with ~10% relative humidity in a heating block. Surviving Salmonella numbers on surfaces were enumerated on a thin agar layer medium. If numbers were below the limit of detection (2.01 log CFU/cm2), Salmonella cells were enriched before plating to determine the presence of viable cells. Water loss (percent) from meat after at 25 and 708C was determined. Whole genomes of Salmonella were interrogated to identify the presence-absence of stress response genes (n ¼ 30) related to dry heat that may contribute to the survival of Salmonella. The survival of Salmonella at 258C was significantly higher across all surfaces (~6.09 to 7.91 log CFU/ cm2) than at 708C (~3.66 to 6.33 log CFU/cm2). On rubber, numbers of Salmonella were less than the limit of detection at 708C. Water loss at 708C (~17.72 to 19.89%) was significantly higher than at 258C (~2.98 to 4.11%). Salmonella cells were not detected on rubber, whereas survival occurred on all red meat at 708C, suggesting its protective effect against the effect of heat. All Salmonella strains carried 30 stress response genes that likely contributed to survival. A multi–antibiotic-resistant Salmonella Typhimurium 2470 exhibited an increase in heat resistance at 708C on beef and lamb compared with other strains. Our work shows that dry heat at 708C for 1 h against Salmonella on red meat is not a practical approach for effectively reducing or eliminating them from red meat.