Polymicrobial Biofilm Interaction Between and .

and are two of multiple agents responsible for bovine respiratory disease (BRD) in cattle. Following respiratory infection of calves with , may also be isolated from the lower respiratory tract. Because may form a biofilm during BRD, we sought to determine if can co-exist with in a polymicrobial biofilm and . Interactions between the two species in the biofilm were characterized and quantified by fluorescence hybridization (FISH). The biofilm matrix of each species was examined using fluorescently tagged lectins (FTL) specific for the exopolysaccharide (EPS) using confocal laser scanning microscopy. Bacterial interactions were determined by auto-aggregation and biofilm morphology. and were evenly distributed in the biofilm, and both species contributed to the polymicrobial biofilm matrix. The average biomass and biofilm thickness, and the total carbohydrate and protein content of the biofilm, were greatest when both species were present. Polymicrobial bacterial suspensions auto-aggregated faster than single species suspensions, suggesting physical interactions between the two species. Almost 300 genes were significantly differentially regulated when the bacteria were in a polymicrobial biofilm compared to a mono-species biofilm, as determined by RNA-sequencing. As expected, host genes associated with inflammation and immune response were significantly upregulated at the infection site following challenge. Encapsulated isolates not capable of forming a substantial biofilm enhanced an polymicrobial biofilm with , indicating they contributed to the polymicrobial biofilm matrix. Indirect evidence indicated that encapsulated also contributed to a polymicrobial biofilm . Only the EPS of could be detected by FTL staining of bovine tissues following challenge with . However, both species were isolated and an immune response to the biofilm matrix of both species was greater than the response to planktonic cells, suggesting encapsulated may take advantage of the biofilm to persist in the host during chronic BRD. These results may have important implications for the management and prevention of BRD.