Abstract
Biofilms have been implicated as an important reservoir for pathogens and commensal enteric bacteria such as Escherichia coli in natural and engineered water systems. However, the processes that regulate the survival of E. coli in aquatic biofilms have not been thoroughly studied. We examined the effects of hydrodynamic shear and nutrient concentrations on E. coli colonization of pre-established Pseudomonas aeruginosa biofilms, co-inoculation of E. coli and P. aeruginosa biofilms, and P. aeruginosa colonization of pre-established E. coli biofilms. In nutritionally-limited R2A medium, E. coli dominated biofilms when co-inoculated with P. aeruginosa, and successfully colonized and overgrew pre-established P. aeruginosa biofilms. In more enriched media, P. aeruginosa formed larger clusters, but E. coli still extensively overgrew and colonized the interior of P. aeruginosa clusters. In mono-culture, E. coli formed sparse and discontinuous biofilms. After P. aeruginosa was introduced to these biofilms, E. coli growth increased substantially, resulting in patterns of biofilm colonization similar to those observed under other sequences of organism introduction, i.e., E. coli overgrew P. aeruginosa and colonized the interior of P. aeruginosa clusters. These results demonstrate that E. coli not only persists in aquatic biofilms under depleted nutritional conditions, but interactions with P. aeruginosa can greatly increase E. coli growth in biofilms under these experimental conditions.
Highlights
In aquatic environments, microorganisms coexist in complex and heterogeneous biofilm communities that exhibit genotypes and phenotypes distinct from their planktonic counterparts [1,2,3]
Biofilms are of particular concern in engineered water distribution systems, as they have been found to harbour pathogens as diverse as enteric viruses, cysts of protozoa such as Cryptosporidium parvum and Giardia lamblia, and bacteria such as Pseudomonas aeruginosa, Escherichia coli, Campylobacter jejuni, Helicobacter pylori, Legionella pneumophila, and Aeromonas spp. [1,3,4,5]
These results show that E. coli can successfully colonize, outcompete, and outgrow established P. aeruginosa biofilms in the nutritionally limited R2A medium
Summary
Microorganisms coexist in complex and heterogeneous biofilm communities that exhibit genotypes and phenotypes distinct from their planktonic counterparts [1,2,3]. Prior studies on the survival of biofilm-associated pathogens [9,10,11,12] suggest that biofilms may play an especially important role in the persistence and dissemination of fastidious and stress-sensitive organisms in the environment [1]. A deeper understanding of the survival and growth potential of pathogens and fecal indicator organisms in aquatic biofilms is needed for the continued improvement of water treatment strategies and identification of potential sources of pathogen contamination. Temperature, nutrient availability, concentration of disinfectants and antagonistic bacterial predation have all been shown to influence the persistence and growth of E. coli in aquatic environments [6,7,15,19]. A detailed description of the flow cell design can be found in Song et al [21]
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