Evaluation of the Inhibition of Culturable Enterococcus Faecium, Escherichia Coli, or Aeromonas Hydrophilia by an Existing Drinking Water Biofilm

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Introduction

Biofilms in potable water distribution systems are well researched (Costerton et al. 1987; LeChevallier et al. 1988; Colbourne et al. 1998), but poorly understood. They consist of microorganisms that can survive and grow under the low nutrient concentrations commonly found within water distribution systems (Frias et al. 1994; Juhna et al. 2007). Biofilms vary in composition and quantity between different systems and are "sensitive to the physicochemical conditions" that influence the ability of microorganisms to grow within the water column and biofilm of drinking water distribution networks (Block 1992; Bois et al. 1997; Momba et al. 2000). Biofilms form throughout drinking water distributions systems. Their development may cause a number of issues, including public health concerns, nuisance issues, aesthetic issues with the water, as well as, being detrimental to operational performance (Ghannoum and O'Toole 2004). Biofilms that contain pathogenic microorganisms could release those organisms into the water column. Biofilms in drinking water distribution systems are known to increase the quantity of microorganisms within the water column of the distribution system during sloughing events as the biofilm breaks (Alary and Joly 1991; van der Wende et al. 1988; Keevil et al. 1989; Reasoner 1988). Studies have attempted to describe the microorganisms within biofilms (LeChevallier et al. 1987; Rogers et al. 1994; Ward et al. 1986); however, biofilm composition is still relatively unknown (Kalmbach et al. 2000).

Microorganisms, which can result in adverse human health effects, have been detected in water distribution systems. While far from the normal conditions for drinking water distribution systems, in rare cases a number of pathogenic and opportunistic microorganisms, such as Pseudomonas, Mycobacterium, Campylobacter, Klebsiella, Aeromonas, Legionella, Helicobacter pylori, and Salmonella typhimurium, have been shown to be present and growing in the biofilms of drinking water systems (Armon et al. 1997; Burke et al. 1984; Mackay et al. 1998; Stelma et al. 2004; Wadowsky et al. 1982). Bacteria that grow in biofilms or multicellular aggregates have greater resistance to antimicrobial treatments than those organisms within the water column (Alary and Joly 1991; Characklis and Marshall 1990; Costerton et al. 1987; Burmolle et al. 2006). Biofilms could act as an additional source of pollution by re-introducing microorganisms into the water column through sloughing, increasing the quantity of microorganisms in the water column that could include human pathogens (Alary and Joly 1991; Berry et al. 2006; Reasoner 1988; van der Wende et al. 1988).

Our previous study of a low dose, long-term cross-connection revealed no evidence of long-term study organism retention within established biofilms (Gibbs et al. 2003). In that study, a distribution system simulator was operated with a direct cross-connection of 0.3% wastewater for 90 days. Following elimination of the cross-connection, water column samples showed that study organisms (total coliforms, Escherichia coli, enterococci, Salmonella, Aeromonas, aerobic endospores, and total culturable heterotrophic organisms) were below the limit of detection within 24 h. However, higher numbers of heterotrophic organisms were detected in the biofilm and water column following the cross-connection, most likely due to the higher nutrient loading of the system. These observations led us to form the hypothesis we evaluated in this study.

The objective of this study was to evaluate the ability of an existing biofilm to reduce the number of introduced microorganisms adhered to materials in an aquatic environment. The study hypothesis was that coupons with no preexisting biofilm (control) would form a biofilm that would maintain more of the study organisms than coupons with an existing biofilm (pre-colonized) following exposure to the study organisms. …