Background: Environmental biofilms can induce attachment and protection of other microorganisms includingpathogens, but can also prevent them from invasion and colonization. This opens the possibility for so-calledbiocontrol strategies, wherein microorganisms are applied to control the presence of other microbes. The potentialfor both positive and negative interactions between microbes, however, raises the need for in depthcharacterization of the sociobiology of candidate biocontrol agents (BCAs). The inside of the drinking water system(DWS) of broiler houses is an interesting niche to apply BCAs, because contamination of these systems withpathogens plays an important role in the infection of broiler chickens and consequently humans. In this study,Pseudomonas putida, which is part of the natural microbiota in the DWS of broiler houses, was evaluated as BCA against the broiler pathogen Salmonella Java.
Results: To study the interaction between these species, an in vitro model was developed simulating biofilmformation in the drinking water system of broilers. Dual-species biofilms of P. putida strains P1, P2, and P3 with S.Java were characterized by competitive interactions, independent of P. putida strain, S. Java inoculum density andapplication order. When equal inocula of S. Java and P. putida strains P1 or P3 were simultaneously applied, theinteraction was characterized by mutual inhibition, whereas P. putida strain P2 showed an exploitation of S. Java.Lowering the inoculum density of S. Java changed the interaction with P. putida strain P3 also into an exploitationof S. Java. A further increase in S. Java inhibition was established by P. putida strain P3 forming a mature biofilmbefore applying S. Java.
Conclusions: This study provides the first results showing the potential of P. putida as BCA against S. Java in thebroiler environment. Future work should include more complex microbial communities residing in the DWS,additional Salmonella strains as well as chemicals typically used to clean and disinfect the system.