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Title: Effect of stomaching on numbers of bacteria recovered from chicken skin

item HANNAH, JACKIE - University Of Georgia
item Cason Jr, John
item Richardson, Larry
item Cox, Nelson - Nac
item Hinton, Jr, Arthur
item Buhr, Richard - Jeff
item SMITH, D - North Carolina State University

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2010
Publication Date: 2/1/2011
Citation: Hannah, J.F., Cason Jr, J.A., Richardson, L.J., Cox Jr, N.A., Hinton Jr, A., Buhr, R.J., Smith, D.P. 2011. Effect of stomaching on numbers of bacteria recovered from chicken skin. Poultry Science. 90:491-493.

Interpretive Summary: Repeated rinses of chicken skin continue to recover about the same number of bacteria as the first rinse. Even with vigorous, semi-destructive agitation, however, only a few more bacteria are recovered from a single rinse. A suggested explanation is that bacteria are held in a water layer on the skin surface and that vigorous agitation breaks the skin into smaller pieces, creating more surface area and a more extensive water layer which traps increasing numbers of bacteria and prevents them from being counted. This experiment added bacteria that were not already present on the skin to see whether vigorous agitation decreased the numbers of added bacteria that could be recovered. That effect was not observed, suggesting that the limited recovery of bacteria after semi-destructive mixing has some other cause.

Technical Abstract: Stomaching of skin samples releases only a few more bacteria than a single rinse. Successive rinses, however, continue to remove almost as many bacteria as the first rinse. One hypothesis to explain this observation is that relatively violent treatment of skin generates smaller pieces of skin, thus increasing the net surface area and effectively sequestering bacteria in a water film on the skin pieces, so that numbers of bacteria suspended in the rinsate do not increase. An experiment was conducted to determine whether inoculated marker bacteria disappear from rinse liquid as skin pieces are stomached and naturally occurring bacteria are released. In each of 4 replications, 5 pre-chill broiler carcasses were collected from a commercial processing plant. Two 5 g pieces (n=40) of breast skin were removed from each carcass and placed in a stomacher bag. An inoculum of 30 mL of 0.85% saline solution containing approximately 104 of a nalidixic acid-resistant Salmonella Typhimurium per mL was added to each sample. Skin samples were hand massaged for 30 s to mix the inoculum, after which a 1 mL aliquot was removed for enumeration of bacteria. A similar sample was taken after 4 min of vigorous stomaching of the skin sample. Bacterial counts recovered from the 30 second hand massage were 4.3, 2.7, 2.6, and 3.7 log10 cfu/mL of rinsate for aerobic bacteria (APC), coliforms, E. coli, and Salmonella, respectively. After stomaching, counts were 4.3, 2.9, 2.8, and 3.8, respectively. There was no difference in APC, but mean coliform and E. coli counts were significantly higher (P<0.05) after stomaching. Numbers of inoculated Salmonella did not decrease. Breaking up skin into smaller pieces by stomaching did not reduce the number of inoculated bacteria suspended in the rinsate.