Planktonic and biofilm community characterization and Salmonella resistance of 14-day old chicken cecal microflora derived continuous-flow cultures

Authors: Crippen, Tawni - Tc; Sheffield, Cynthia; Andrews, Kathleen - Kate; Dowd, Scot; Nisbet, David

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2008
Publication Date: 10/1/2008
Citation: Crippen, T.L., Sheffield, C.L., Andrews, K., Dowd, S.E., Nisbet, D.J. 2008. Planktonic and biofilm community characterization and Salmonella resistance of 14-day old chicken cecal microflora derived continuous-flow cultures. Journal of Food Protection. 71:1981-1987.

Interpretive Summary: The design of more effective methods to control both the spread of pathogenic organisms and antimicrobial resistance within preharvest food animals relies upon gaining a better understanding of how bacterial communities are formed and interact. Competitive exclusion is a strategy which utilizes the introduction of a mix of harmless bacteria as a method of preventing colonization by disease-causing bacteria. Its purpose is to reduce the need for chemical antibiotics to control disease-causing bacteria in food animals. The mix of bacteria used is often based on material originally obtained from healthy adult animals. In the case of poultry, young animals are at risk of bacterial infection by Salmonella, but that vulnerability decreases as the chick matures. The likelihood of acquiring a Salmonella infection at two weeks of age in poultry is low and represents a shift to protection from colonization by the bird’s native gut bacteria. In addition, the community structure of bacteria within the intestinal tract is less complex at this younger age than at adulthood. We analyzed the makeup and ability to repel Salmonella colonization from the cecal bacterial community of 14-day-old chicks. This work explores the minimal bacterial make-up of effective competitive exclusion treatments to better ensure the health of both food animals and consumers.

Technical Abstract: These studies were initiated to compare the composition of GIT bacterial communities in birds during the transition period in age where their susceptibility to Salmonella shifts to resistance. One of the challenges to developing probiotics is to develop an efficacious culture of minimal diversity, e.g. one that includes the bacteria that are vital contributors to protection from pathogens and excludes unnecessary species. We used in vitro continuous-flow culture techniques to test the ability of mixed bacterial cultures, acquired from in vivo sources, to resist colonization by a marker Salmonella and then characterized the constituents of the cultures. In previous studies by this lab, cecal bacterial cultures initiated from 1-day-old chicks were unable to abolish colonization by Salmonella and cultures initiated from 7-day-old chicks had variable success resisting colonization by Salmonella. The cultures initiated from 14-day-old chicks were all able to completely restrict colonization by Salmonella. Both biofilm and planktonic communities were characterized. Eighteen species of bacteria from ten different genera were characterized, including the lactic acid producing bacteria from the Bifidobacterium, Enterococcus, Gemella and Pediococcus genera. However, each culture contained an mixture of only eleven species. Biofilms contained less than 50% of the species found in the planktonic communities. After challenge, it took an average of 10 days to clear the invading Salmonella from the culture. While not adults, the diversity of microbes within the in vitro cecal cultures from 14 day old birds represent a community complex enough to oppose invasion by a pathogenic organisms in vitro.