Survival of legionella pneumophila and salmonella typhimurium in biofilm systems

Abstract

Biofilms are found in many water supply systems where they form an environment in which different bacteria can be entrapped for long periods. Besides the aesthetic aspect, biofilm has a major contribution in biocorrosion, disinfection inefficiency and possibly may act as a reservoir for pathogenic and non-pathogenic microorganisms. In the present study, two pathogenic bacteria Legionella pneumophila and Salmonella typhimurium WG-49 were introduced into a biofilm simulation flow system supplied with sterile and non-sterile tap water. The survival of these microorganisms into the biofilm formed on glass and PVC coupons at two temperatures (24°C and 36°C) was compared in this system. On glass supports, under sterile conditions at 36°C, Legionella pneumophila sg3 decreased by 6 logs during 40d continuous recirculation. Under non-sterile conditions, L. pneumophila decreased by only half log <48d. S. typhimurium WG-49 under the same conditions showed an increase of 3 logs in the sterile system for 31d, while in the non-sterile system it dropped by only 0.5 log for 20d. At 24°C, L. pneumophila remained stable for >40d under sterile conditions. In non-sterile conditions, L. pneumophila dropped by 1 log for 35d. S. typhimurium, in a sterile system, remained almost unchanged, while in the non-sterile system an increase of 3 logs was observed for the first 21d and thereafter a decrease of 2 logs for the next 21d of the experiment. L. pneumophila on PVC coupons at 36°C survived better compared with glass support. The experimental data show that survival of pathogenic microorganisms into biofilm is variable and depends on many factors, making the survival prediction a difficult task. However, the survival results of L. pneumophila and S. typhimurium in time terms should raise important questions on their potential threat in water distribution systems.

Comparing the effect of various pipe materials on biofilm formation in chlorinated and combined chlorine-chloraminated water systems

“…Bacterial biofilms developing in distribution systems receiving chlorinated water have been repeatedly reported by previous investigators (LeChevallier et al, 1987(LeChevallier et al, , 1988(LeChevallier et al, , 1990Van der Wende and Characklis, 1990; Camper et al, , 1998,1999, 2000, 2002). Although the present investigation did not deal with the identification of various pathogenic and opportunistic pathogens, the survival and multiplication of heterotrophic bacteria such as Escherichia coli, Pseudomonas, Aeromonas, Klebsiella, Legionella spp., Mycobacterium, Campylobacter, Salmonella typhimurium and Helicobacter pylori have been observed within biofilms occurring in potable water systems with standard chlorine residual concentrations (Engel et al, 1980;Wadowsky et al, 1982;Burke et al, 1984;Armon et al, 1997;Mackey et al, 1998;Camper et al,1999;Momba et al, 1999). The capability of E. coli to survive a high free chlorine residual dose of 0.7 mg·l -1 and to attach on pipe materials such as stainless steels was reported by Momba and coworkers in 1999.…”

Detection of Escherichia coli in Biofilms from Pipe Samples and Coupons in Drinking Water Distribution Networks

“…Several studies at the lab scale have demonstrated that even in the presence of detectable levels of chlorine, E. coli can be incorporated in biofilms (34), survive in the biofilm for up to 40 days (1,17), and persist there in a metabolically active form (13,40). Some authors suggest that E. coli can even grow in drinking water distribution systems (7) because these bacteria can adapt to the oligotrophic environment.…”

“…It has also been shown that bacteria attached to surfaces show greater resistance to disinfection (15,19,20,36). Biofilms in distribution systems may provide a favorable condition for some bacteria, such as opportunistic pathogens (e.g., Legionella spp., Pseudomonas aeruginosa, and Mycobacterium avium), to colonize it and may harbor pathogens, such as Salmonella enterica serovar Typhimurium, which have entered the distribution system (1,5,18,28). It has been shown in lab-scale experiments that E. coli can survive in biofilters (24) and even multiply in the biofilm (17,34,40), which again raises the question of its suitability as a drinking water quality indicator.…”

Persistence and Decontamination of Bacillus atrophaeus subsp. globigii Spores on Corroded Iron in a Model Drinking Water System

“…Multiple studies have shown that Legionella pneumophila can persist in or on simulated drinking water biofilm (3,11,19,26,36), as can Helicobacter pylori, but the results are limited (23,28). Virus persistence has also been demonstrated, but published results have been variable (19,29,35).…”

“…However, information on persistence of microbiological agents in water distribution system pipe material is limited. Research available in the open literature mostly focuses on bacteria, including coliforms (7,12,25,37), Helicobacter pylori (23, 28), Legionella pneumophila (3,11,19,26,36), Aeromonas hydrophila (5), and Salmonella enterica serovar Typhimurium (3). Other researchers have investigated the persistence of injected viruses (19,29,35) as well as wastewater cross-connections with drinking water pipes (13, 24).…”