Prevalence, levels and viability of Salmonella in/on raw chicken livers

Authors: Jung, Yang Jin; Porto-Fett, Anna; Shoyer, Brad; Henry, Elizabeth; Shane, Laura; Osorio, Manuela; Luchansky, John

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2019
Publication Date: 4/10/2019
Citation: Jung, Y.N., Porto Fett, A.C., Shoyer, B.A., Henry, E.D., Shane, L.E., Osoria, M., Luchansky, J.B. 2019. Prevalence, levels and viability of Salmonella in/on raw chicken livers. Journal of Food Protection. 82(5):834-843.

Interpretive Summary: Chicken liver is commonly used to prepare pate, but consumers prefer pate that is pinkish in color rather than greyish in color, and the pinkish color is usually the result of undercooking. If Salmonella were present in or on a high percentage of raw chicken livers/parts and at relatively high levels, then undercooking would present a palpable threat to public health. In fact, there have been at least 28 chicken-liver-associated outbreaks caused by Salmonella or Campylobacter between 2000 and 2016. Thus, we surveyed chicken livers for the presence and levels of Salmonella spp. The pathogen was recovered from 148 of 249 (59.4%) retail chicken liver samples at levels of 6.5 to 8.0 estimated viable cells per gram. For comparison, we also sampled raw chicken livers that were harvested from birds residing on a research farm and recovered Salmonella from 12 of 207 (5.8%) of livers tested at levels of less than 2.2 estimated viable cells of the pathogen per gram of chicken liver. In phase II of our study, we inoculated raw chicken livers with Salmonella to determine if the pathogen would survive storage in a refrigerator or freezer. We observed a decrease of 10 to 100 cells per gram of liver during cold storage within ca. 2 days to 2 weeks, respectively. Our results confirmed that Salmonella were recovered from about 60% of livers purchased at retail and from about 6% of livers harvested directly from birds on a research farm at levels that could cause human illness in the event of undercooking or improper handling or storage. In conclusion, without question cooking remains the most direct, easy, and cost-effective way to eliminate Salmonella from livers/pate.

Technical Abstract: We surveyed chicken livers from various sources for the presence and levels of Salmonella spp. The pathogen was recovered from 148 of 249 (59.4%) chicken livers purchased at retail stores in Delaware, New Jersey, and Pennsylvania over a ca. 9-month period; positive samples harbored Salmonella at levels of 6.4 ± 20.2 to 8.0 ± 22.1 MPN per gram. The proportion of samples testing positive for Salmonella for livers purchased at retail outlets in New Jersey (72%, 59 of 82 livers) was significantly higher than for livers purchased at retail outlets in Pennsylvania (57.6%, 53 of 92 livers) or Delaware (48%, 36 of 75 livers). The pathogen was also recovered more often from livers that were packaged by retailers (81 of 121 livers; 66.9%) compared to liver samples packaged directly by processors (67 of 128 livers; 52.3%). Of note, the 128 livers purchased as pre-packaged were comprised of 6 brands that were collected on 118 total visits to some 59 stores; Salmonella were recovered from Brand B (22.3%; 33 of 148 total positive samples) far more often than any other brands, including Brand D (12.2%; 18 positive) which yielded the second most positive samples. In addition, 12 of 207 (5.8%) chicken livers harvested from birds on a research farm tested positive for Salmonella at levels ranging from 0.4 ± 0.5 MPN per gram to 2.2 ± 3.3 MPN per gram. The recovery rate for livers with the gall bladder attached was 4.4% (6 of 135 livers), whereas it was 8.3% (6 of 72 livers) when the gall bladder was removed from the liver. As a second objective, we quantified the levels of a nine-strain cocktail (ca. 6.5 log CFU per gram) of Salmonella spp. inoculated externally or internally onto/into livers both before and after extended cold storage. In brief, storage for at least 2 d at 4 degree C or 15 d at minus 20 degree C resulted in a decrease of ca. 1.0 log CFU per gram in pathogen levels. Given the relatively high recovery rate (ca. 6.0 to 60.0%) and illness-causing populations (average of 0.4 to 10 MPN per gram) of Salmonella associated with chicken livers in the present study, our data argue strongly for additional interventions for processors to lower the prevalence and levels of this pathogen on raw liver along with more focused efforts directed towards both chefs and consumers to ensure that liver/pâté is properly cooked and served prior to human consumption.