Isolation and Identification of Listeria spp., Staphylococcus aureus, and Salmonella during Dry Aging

Introduction: Dry aging is one of the aging processes, especially for beef. Dry aging was used in the past, but it disappeared after the refrigerator was invented. This aging process is becoming popular because it produces flavor and texture, which consumers like. However, food safety concerns for the process have been raised.

Purpose: The objective of this study was to investigate the prevalence of Listeria spp., Staphylococcus aureus, and Salmonella in beef carcasses during dry aging.

Methods: Surface samples from 27 beef carcasses and 26 environmental samples (door knob, knife, tray, cutting board, shelve, and fans in aging room) in dry aging room by swabbing method with sterile gauze. Swab samples were then plated on Palcam agar (Listeria spp.), mannitol salt agar (Staphylococcus aureus), and xylose-lysine-desoxycholate agar (Salmonella). Typical colonies from each plate were further analyzed by 16S rRNA analysis and PCR for identification. To detect toxigenic genes in each isolates, PCR were performed using the primers specific to pathogenic genes.

Results: Of 27 carcass samples, Listeria spp. were isolated from three samples (11.1%), and two samples had Listeria ivanovii (7.4%) and one sample had Listeria monocytogenes (3.7%). Staphylococcus aureus was also isolated from 16 samples (59.3%), but there were no samples contaminated with Salmonella. Of 26 environmental samples, two samples (7.7%; one cutting board and one shelf) were contaminated with Salmonella. Listeria monocytogenes (3.9%) was, also, isolated from the cutting board. The L. monocytogenes isolates had pathogenic genes such as hlyA and prs.

Significance: These results indicate that food safety criteria need to be established to improve food safety for dry aging beef.