Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2009
Publication Date: 9/17/2009
Citation: Sheffield, C.L., Crippen, T.L., Andrews, K., Bongaerts, R.J., Nisbet, D.J. 2009. Planktonic and biofilm communities from 7-day-old chicken cecal microflora cultures: Characterization and resistance to Salmonella colonization. Journal of Food Protection. 72:1812-1820. Interpretive Summary: The treatment of animals with a mix of harmless bacteria in an attempt to prevent infection from disease-causing bacteria is a strategy called competitive exclusion. This strategy is used in place of chemical antibiotics to control disease-causing bacteria in food animals. This mix is originally harvested from healthy animals and its bacterial make-up must be determined prior to its use in competitive exclusion treatment. Competitive exclusion treatments or cultures can be prepared using a chemostat. A chemostat is a closed vessel system that provides a constant flow of nutrients and an anaerobic atmosphere for the mix of many different bacterial species which make up the competitive exclusion culture. The culture is a combination of bacterial communities found in both the liquid (planktonic) and solid (biofilm) portions of the culture. The biofilm is made up of bacteria which stick to the inside of the chemostat vessel. In the present study, a technique called automated ribotyping was used to identify the bacteria present in both the planktonic and biofilm communities from six mixed bacterial cultures started from chicken cecal material collected from 7-day old chicks. Ribotyping provided rapid and precise identification of the individual species of bacteria contained within the mixed culture. In total, 13 species of bacteria were found among the six cultures. Overall, planktonic communities were more diverse than the biofilm communities. Twothirds of the planktonic bacterial communities contained six or more species of bacteria. In contrast, only one-third of the biofilm bacterial communities contained more than three species of bacteria. Klebsiella pneumoniae was the only organism found in all planktonic communities. Both the biofilm and planktonic communities contained lactic or propionic acid bacteria from three genera, Bacteroides, Pediococcus, and Enterococcus. Other researchers have shown that the formation of bacterial communities on solid surfaces are an important strategy for bacterial survival in a number of environments and these communities may play a key role in the expansion of antibiotic resistance among bacteria within agricultural environments. By better understanding how microbial communities are formed and interact with each other we will be able to design more effective methods to control both the spread of antimicrobial resistance and pathogenic organisms within preharvest food animal production environments.
Technical Abstract: Over the last few years, both scientific organizations and regulatory agencies have focused on the use of antimicrobial agents in food animals and the related risk of developing antibiotic resistance. Despite increased information relating to the importance of bacterial biofilms and their potential as a contributory factor in the development of bacterial resistance there is a lack of information relating to the role of biofilms in the development and maintenance of effective competitive exclusion cultures. We characterized and compared the biofilm and planktonic communities within continuous flow cultures of chicken cecal microflora from 7-day old chickens using automated ribotyping. Six culture systems were examined and 13 species from eight different genera were identified. The planktonic community exhibited the most diversity with 67% containing six or more species of bacteria from five or more genera. In contrast, only one-third of the biofilm community contained more than three species of bacteria. Enterococcus faecalis was the most frequently isolated species, found in the either the planktonic or biofilm community in 83% of the cultures. Klebsiella pneumoniae was the only organism found in all planktonic communities. Both the biofilm and planktonic communities contained lactic or propionic acid bacteria from three genera, Bacteroides, Pediococcus, and Enterococcus. This study provided a molecular based characterization of both the biofilm and planktonic communities found in culture systems derived from the cecal microflora from 7-day old chickens.