An Approach for Mapping the Number and Distribution of Salmonella Contamination on the Poultry Carcasst

Mapping the number and distribution of Salmonella on poultry carcasses will help guide better design of processing procedures to reduce or eliminate this human pathogen from poultry. A selective plating media with multiple antibiotics (xylose-lysine agar medium [XL] containing N-( 2-hydrox yethyl)piperazineN'(2ethanesujfonic acid) and the antibiotics chioramphenicol, ampiciflin, tetracycline, and streptomycin [XLH-CATS]) and a multiple-antibiotic-resistant strain (ATCC 700408) of Salmonella Typhirnurium definitive phage type 104 (DTI04) were used to develop an enumeration method for mapping the number and distribution of Salmonella Typhimurium DTI04 on the carcasses of young chickens in the Cornish game hen class. The enumeration method was based on the concept that the time to detection by drop plating on XLH-CATS during incubation of whole chicken parts in buffered peptone water would be inversely related to the initial log number (N0) of Salmonella Typhimurium DTI04 on the chicken part. The sampling plan for mapping involved dividing the chicken into 12 parts, which ranged in average size from 36 to 80 g. To develop the enumeration method, whole parts were spot inoculated with 0 to 6 log Salmonella Typhimurium DTI04, incubated in 300 ml of buffered peptone water, and detected on XLH-CATS by drop plating. An inverse relationship between detection time on XLH-CATS and No was found (r = — 0.984). The standard curve was similar for the individual chicken parts and therefore, a single standard curve for all 12 chicken parts was developed. The final standard curve, which contained a 95% prediction interval for providing stochastic results for N0, had high goodness of fit (r2 = 0.968) and was No (log) = 7.78 ± 0.61 (0.995 x detention time). Ninety-five percent of No were within i:0.61 log of the standard curve. The enumeration method and sampling plan will be used in future studies to map changes in the number and distribution of Salmonella on carcasses of young chickens fed the DTI04 strain used in standard curve development and subjected to different processing procedures. Mapping the number and distribution of Salmonella contamination on poultry carcasses is a high priority research area for the U.S. Department of Agriculture, Food Safety and Inspection Service, because it will allow better targeting of sampling for Salmonella detection, and it will allow better design of processing procedures to reduce or eliminate this human pathogen from poultry carcasses. However, there are no reports in the scientific literature demonstrating how to map the number and distribution of Salmonella on poultry carcasses. Therefore, the general objective of this study was to develop an approach for quantitative mapping of Salmonella contamination on poultry carcasses. The approach taken was to divide carcasses of young chickens (28 days of age) in the Cornish game hen class into 12 parts as an initial sampling plan for future mapping studies. Cornish game hens were used because their small size allowed use of less isolation media and made it easier to develop mapping concepts, and because little informa* Author for correspondence. Tel: 410-651-6062 Fax: 410-651-8498: E-mail: [email protected]. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply revoilloicudation or endorsement by the U.S. Department of Agriculture. tion is available about the level of Salmonella contamination on this class of poultry. The carcass rinse method coupled with the most-probable-number method is the most common approach used to enumerate Salmonella contamination on chicken carcasses. A limitation of the carcass rinse method is that it does not recover all bacteria, including Salmonella, from the chicken carcass (9, ii) and thus, is less sensitive at detecting Salmonella than is the whole-part incubation method (5, 16). Chen et al. (4) demonstrated that the drop-plate method is a low-cost and simple direct-plating method for quantifying bacteria in culture media. Blackburn and Davies (3) reported that a selective agar medium (i.e., xylose-lysine) supplemented with antibiotics can be used to recover multiple-antibiotic-resistant (MAR) Salmonella by direct plating from food-sample incubations. These studies indicate that drop plating onto a selective agar medium with multiple antibiotics might be a cost-effective method for enumerating MAR Salmonella in whole-part incubations. Recently, a selective media (xylose-lysine agar medium IXT.1 containing N-(2-hydroxyethyl)piperazine-N'-(2-ethane fonic acid) IHEPESJ and the antibiotics chlorampheni ampicil lin, tetracycline, and streptomycin [XLH-CAT.' was developed for detection and enumeration of a MU strain of Salmonella Tvpliimurium DTI 04 in chicken Sfl! I 1786 OSCAR Food Prot., Vol. 71, No. 9 TABLE 1. Weight and experimental design for inoculation of chicken parts with Salmonella Typhimurium DTJ04: dilution of culture used for inoculation in each trial Chicken part Chicken part wt (g) Trial(s) Code Name Mean SD I, 7 2, 8 3 4, 9, 10 5, 11 6, 12 Wing, left 42.9 2.3 -7a —2 —3 —4 —5 —6 Wing, right 42.4 7.8 —7 —2 —3 —4 —5 —6 Breast, front left 56.1 6.8 —6 —7 —2 —3 —4 —5 Breast, front right 56.9 9.2 —6 —7 —2 —3 —4 —5 Breast, back left 36.1 5.5 —5 —6 —7 —2 —3 —4 Breast, back right 40.3 3.7 —5 —6 —7 —2 —3 —4 Back, rib 70.8 12.6 —4 —5 —6 —7 —2 —3 Back, sacrum 80.2 15.4 —4 —5 —6 —7 —2 —3 Thigh, left 51.5 8.1 —3 —4 —5 —6 —7 —2 Thigh, right 49.5 4.7 —3 —4 —5 —6 —7 —2 Drumstick, left 43.6 4.5 —2 —3 —4 —5 —6 —7 Drumstick, right 47.4 3.0 —2 —3 —4 —5 —6 —7 a Dilutions of —7, —6, —5, —4, —3, and —2 correspond to initial log doses of 0.5 to 1, 1.5 to 2, 2.5 to 3, 3.5 to 4, 4.5 to 5, and 5.5 to 6, respectively. pies, with other microorganisms (13, 14). Therefore, the specific objective of this study was to develop a standard curve for enumerating Salmonella Typhimurium DTI04 on Cornish game hen carcass parts by drop plating on XLHCATS, for use in future mapping studies with MAR strains