Interaction between non-disease causing microorganism and E. coli in catheter-associated urinary tract biofilms

Abstract

Most biofilms involved in catheter-associated urinary tract infections (CAUTIs) are polymicrobial, with disease causing (e.g. E. coli) and non-disease causing (NDC) microorganisms (Delftia tsuruhstensis, Achromobacter xylosoxidans, Burkholderia fungorum) frequently co-inhabiting the same catheter. Nevertheless, there is a lack of knowledge about the role that NDC microorganisms have on biofilm formation by E. coli. This information is essential for a better understanding of CAUTIs etiology. As such, single- and dual-species biofilms were formed in 96-well microtiter plates, using artificial urine medium (AUM). Biofilm quantification was evaluated by crystal violet staining, CFU counts and DAPI counts at 24h, 48h, 96h and 192h. In single-species biofilms, results showed that all species were able to form biofilms (Log 5.84-7.25 CFUs.cm2 at 192h). Concerning dual species biofilms, E. coli appears to have a negative impact on the ability of the NDC species to form biofilms, but, NDC species do not seem to influence E. coli when the two species start forming the biofilm simultaneously and at the same concentration. In fact, the growth rate of E. coli (0.4564 h-1) in AUM is higher than the growth rates of NDC microorganisms (0.0458 h-1–0.131 h-1). Additionally, in dual-species biofilms with an E. coli pre-formed biofilm, the E. coli seems to prevail, even in conditions with a low initial inoculum concentration (102 CFUs.ml-1 vs. 108 CFUs.ml-1 for NDC microorganisms). In conclusion, E. coli has a greater ability to form biofilm in conditions mimicking the CAUTIs, which helps explain why E. coli is the most prevalent agent in CAUTIs.