Hygienically Relevant Microorganisms in Biofilms of Man-Made Water Systems

Abstract

In recent years, it has become evident that biofilms in drinking water distribution networks and other man-made water systems can become transient or long-term habitats for hygienically relevant microorganisms. Important categories of these organisms include faecal indicator bacteria (e.g. Escherichia coli), obligate bacterial pathogens of faecal origin (e.g. Campylobacter spp.), opportunistic bacteria of environmental origin (e.g. Legionella spp., Pseudomonas aeruginosa), enteric viruses and parasitic protozoa (e.g. Cryptosporidium parvum). These organisms can attach to preexisting biofilms, where they become integrated and survive for days to weeks or even longer, depending on the biology and ecology of the organism and the environmental conditions. There are indications that at least part of the biofilm populations of pathogenic bacteria persist in a viable but non-culturable state. Thus, biofilms in man-made water systems can function as an environmental reservoir for pathogenic microorganisms and present a potential source of water contamination, resulting in a health risk for humans. This review outlines the current knowledge of the integration and fate of hygienically relevant microorganisms in biofilms of man-made water systems, with consideration of the physicochemical and biological factors that govern these processes.