Prevalence of Nalidixic Acid Resistant Salmonella Species on Chicken Skin with Commercial Marinades
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Marination of poultry meat is widely done in the industry not only for value addition but also to enhance the shelf life. In addition to increased consumer acceptance the combination of spices in marinades have a potential to inhibit microbial growth in poultry products. A series of experiments were conducted to determine the efficacy of commercial teriyaki and lemon pepper marinades on viability of multiple strains of nalidixic acid (NAL) resistant Salmonella. NAL resistant Salmonella (Typhimurium, Heidelberg and Senftenberg) cultures were developed by inoculating BHI broth and incubating for 24 h at 37 °C; subjecting strains to increasing concentrations of NAL in XLT4. As a result, S. Typhimurium and S. Heidelberg resistant to 60 µgm and S. Senftenberg resistant to 35 µgm of NAL were obtained. These strains were inoculated in 9 ml of BHI and incubated for 24 h at 37 °C; followed by transferring 100 µl of inoculum into 40 ml of BHI and incubating for 20 h at 37 °C. Each strain was individually inoculated (ca. 106-8 CFU/ ml) into either teriyaki and lemon pepper marinade, maintained at 4 and 25 °C, and samples were drawn after 0, 4, 8, 16, 24, and 32 h. Serial dilutions of inoculated marinade were made and surviving populations (log10 CFU/ ml) of Salmonella were enumerated by plating 0.1 ml onto XLT4 agar. Plates were incubated at 37 °C for 24 h. Teriyaki marinade significantly (p < 0.05) lowered the counts of Salmonella throughout the study as compared to Lemon pepper irrespective of the time and temperature of storage. S. Heidelberg and Typhimurium populations were significantly lowered (p<0.05) as a result of an interaction effect of marination time and type of marinade used whereas survival populations of S. Senftenberg were significantly lowered (p<0.05) as a result of a three way interaction between marination time, type of marinade, and temperature at which the marinades were stored. These findings suggest that marination would be a promising approach in developing antimicrobial systems for poultry products. Based on the results of this experiment, an experiment was conducted to determine the prevalence of Salmonella strains on the chicken skin when marinated with Teriyaki and Lemon pepper marinades. The NAL resistant strains were cultured individually in BHI ay 37 °C for 20 h. These cultures were then serially diluted in peptone water and 10¹, 10², 10³ and 10⁴ CFU/ml were used as inoculum levels to inoculate the skin. Chicken skin from the breast was inoculated with 100 µl of inoculum from 0.6 to 3.14 log10 CFU/ g in a 12-well titer plate and placed under a bio-safety hood for 30 minutes to allow bacterial attachment followed by marination with teriyaki or lemon pepper marinades, respectively. Marinated samples were stored at room temperature (25 ºC) and refrigeration temperature (4 °C) for up to 32 h. Samples were removed from the marinades at 0, 4, 8, 16, 24 and 32h and plated in duplicates onto XLT4 followed by incubation of the plates at 37 ºC for 24 h. The results were analyzed using Analysis of variance (ANOVA) in SAS and the significance was reported at p < 0.05. Prevalence of Salmonella was significantly reduced (p < 0.05) by teriyaki marinade at all levels of contamination. Lemon pepper reduced the prevalence at low levels of contamination (10¹ and 10² CFU/gm) whereas no significant effect (p > 0.05) was observed at higher levels of contamination. There was no significant (p > 0.05) difference observed at the two storage temperatures, 4 and 25 °C, except for S. Typhimurium which show significant reduction with lemon pepper marinade at 4 °C. Marination of chicken skin greatly helped in the reduction of prevalence of Salmonella spp irrespective of the temperature of storage indicating antimicrobial potential in addition to enhancing shelf life of poultry and meat products.
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