Interaction of Salmonella with E. coli and Proteus spp. in Biofilm Formation
Authors: Pathiranage S. U. , Madushanka D. N. N. , Hasintha K. V. D. M. , Nadishani H. C. , Fernando G. C. P. , Jayaweera T. S. P. , Ruwandeepika H. A. D. 
Published: December 2021

Aims: Investigate the interaction of Salmonella spp. with E. coli and Proteus spp. in biofilm formation as mono and dual-species at different time durations
Experimental Design: Salmonella, Proteus, and E. coli were isolated from Broiler chicken meat, and the biofilm-forming ability of these organisms were studied.
Place and Duration of Study: The study was conducted at the Laboratory of Livestock Production, Faculty of Agricultural Sciences, Sabaragamuwa University of Sri Lanka, from 2019 December to 2020 May.
Methodology: This study investigated the biofilm-forming ability of Salmonella as a mono species and its interaction with E. coli and Proteus in the process of biofilm formation. Microorganisms used for this study were isolated from broiler chicken meat. Biofilm was quantified using a microtitre plate assay. The interaction effects were tested at the temperature of 280C in different time durations (up to 120 hours).
Results: Salmonella 1 and Proteus monocultures showed significantly higher biofilm-forming ability than Salmonella 3 isolate at all tested time points. At 120 hr, additionally to the salmonella 1 and Proteus isolates E. coli also formed significantly higher biofilms than Salmonella 3. However, Salmonella 3 was the lowest biofilm former as mono biofilm at all tested time durations. Salmonella 1 interaction with Salmonella 3 isolates formed less biofilms than Salmonella 1 mono biofilm at 48hr and 72hr correspondingly. Salmonella 1 and its interactions with Salmonella 3, Proteus, E. coli showed similar biofilm-forming abilities without significant differences at all other tested time points. Specifically, Salmonella 3 interaction with Salmonella 1 as dual biofilm showed higher biofilm-forming ability than Salmonella 3 mono biofilm at all tested time points. Tested isolates and their interaction achieved the highest biofilm formation at numerous time points. In fact, at 48hr, Salmonella 3 isolates and its interaction of Proteus, E. coli, and Salmonella 1 interaction with Proteus attained their highest biofilm formation abilities. The highest biofilm formation was achieved by Salmonella 1 isolate as mono biofilm and Salmonella 1 interaction with E. coli as dual biofilm at 72hr. Biofilm-forming trend of respective isolates and interactions showed numerous patterns at tested time durations.
Specifically, E. coli rapidly enhanced its biofilm-forming ability as monoculture from 24 hr to 120 hr. Proteus, Salmonella 3 as monocultures, Salmonella 3 interaction with Proteus and E. coli as dual cultures showed progressive biofilm development from 24 hr to 48 hr. Salmonella 1 monoculture and its interaction with Salmonella 3, E. coli as dual biofilm improved their biofilm-forming ability from 24 hr to 72 hr. Similar to Salmonella 3 interaction with Proteus, Salmonella 1 interaction with Proteus also increased its biofilm-forming ability from 24 hr to 48 hr.
Conclusions: This study concluded that there is a variation among isolates and their combinations in forming the biofilms, where there is an enhancement of biofilm in dual-species over the mono-species in some interaction, and there is a reduction in biofilm formation by dual-species with some combinations. Further, this concluded that Salmonella is interacting with other commonly found bacteria such as Proteus and E. coli in biofilm formation.