Short communicationAn in vitro model of catheter-associated urinary tract infections to investigate the role of uncommon bacteria on the Escherichia coli microbial consortium

•E. coli and D. tsuruhatensis are able to form single- and dual-species biofilms.•Both bacteria tend to co-aggregate and cooperate over time.•E. coli and uncommon bacteria persist in a stable microbial community.

Uncommon bacteria, such as Delftia tusurhatensis have been isolated from CAUTIs in combination with well-established pathogenic bacteria such as Escherichia coli. Nonetheless, the reason why E. coli coexists with other bacteria instead of outcompeting and completely eliminating them is unknown. As such, a flow cell reactor simulating the hydrodynamic conditions found in CAUTIs (shear rate of 15 s−1) was used to characterize the microbial physiology of E. coli and D. tsuruhatensis individually and in consortium, in terms of the growth kinetics and substrate uptake. Single-species biofilms showed that up to 48 h the cultivable cell counts significantly increased for both species (p < 0.05). When in dual-species biofilm, E. coli outnumbered D. tsuruhatensis up to 16 h and then D. tsuruhatensis gained a fitness advantage. However, the assessment of the spatial distribution of the dual-species biofilm by LNA/2′OMe-FISH revealed that E. coli and D. tsuruhatensis coexist and tend to co-aggregate over time, which suggests that both bacteria are able to cooperate synergistically. Substrate uptake measurements revealed that D. tsuruhatensis metabolized citric acid more rapidly, presumably leaving more uric acid available in the medium to be used by E. coli. In conclusion, E. coli and uncommon bacteria seem to cooperate, when sharing the same environment under dynamic conditions, leading to the persistence of both bacteria in a stable microbial community.