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ARS Home » Research » Publications at this Location » Publication #173319


item Smith, Douglas
item Cason Jr, John
item Berrang, Mark

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2005
Publication Date: 7/1/2005
Citation: Smith, D.P., Cason Jr, J.A., Berrang, M.E. 2005. Effect of fecal contamination and cross contamination on numbers of coliform, escherichea coli, campylobacter and salmonella on immersion chilled broiler carcasses. Journal of Food Protection. 68(7):1340-1345.

Interpretive Summary: Almost all chickens processed in the U.S. are immersion chilled to improve the safety and quality of the product, through reducing the levels of pathogenic bacteria and increasing shelf life. There have been reports that the chilling process may allow a few contaminated carcasses to spread bacteria to many other carcasses. An experiment was designed to determine if the chilling process does remove bacteria from carcasses but allows cross contamination to occur. This experiment tested this hypothesis under impaired chilling conditions, and did not use any additional bacterial reduction methods employed in the processing industry, such as pre-chill spray washing, antimicrobials prior to or in the chiller, or continuous fresh water added to the chiller. A fecal mixture was applied to some carcass halves prior to chilling, and other uncontaminated halves were placed either into the same chiller with the contaminated carcasses or into an identical, uncontaminated chiller. Bacterial counts were then measured after chilling. Immersion chilling, even under less than optimum conditions, lowered the counts of general bacteria (coliforms and E. coli) and pathogens (Campylobacter and Salmonella), and reduced the incidence of pathogenic bacteria on contaminated carcasses. However, cross contamination of control carcasses with pathogenic bacteria did occur. Immersion chilling is effective at lowering bacterial counts, but other methods already commonly used in the poultry industry are necessary to prevent or eliminate cross contamination

Technical Abstract: The effect of pre-chill fecal contamination on numbers of bacteria on immersion chilled carcasses was tested in each of three replicate trials. For each trial, 16 eviscerated broiler carcasses were split into 32 halves and assigned to one of two groups. Cecal contents (0.1 g inoculated with Campylobacter and naladixic acid resistant Salmonella) were applied to each of eight halves in one group (Direct contamination) that were placed into one paddle chiller (Contaminated), while the other paired halves were placed into another chiller (Control). From the second group of 8 split birds, one of each paired half was placed in the Contaminated chiller (to determine Cross contamination) and the other halves were placed in the Control chiller. Post-chill carcass halves were sampled by a 1 min rinse in sterile water, which was collected and cultured; results are reported as log10 CFU/ml rinsate. There were no significant statistical difference (paired t test, P<0.05) due to Direct contamination of halves for coliforms (3.0 vs. 3.0 log CFU) and E. coli (2.6 vs. 2.7 log CFU), although Campylobacter numbers significantly increased from control values due to Direct contamination (1.5 vs. 2.1 log CFU), and incidence increased from 79 to 100%. There was no significant effect of Cross contamination on coliform (2.9 vs. 2.9 log CFU) or E. coli (2.6 vs. 2.6 log CFU) numbers, although Campylobacter was significantly higher after exposure to cross contamination (1.6 vs. 2.0 log CFU), and incidence increased from 75 to 100%. Salmonella-positive halves increased from 0 to 42% post-chill due to Direct contamination, and from 0 to 25% as a result of Cross contamination after chilling. Water samples and surface swabs taken post-chill from the Contaminated chiller were higher for Campylobacter than the Control chiller. Immersion chilling equilibrated bacterial numbers between contaminated and control halves subjected to either Direct or Cross contamination for coliforms and E. coli. Campylobacter numbers, Campylobacter incidence, and Salmonella incidence increased due to both Direct and Cross contamination in the chiller.