- Top of page
- Materials and Methods
- Results and Discussion
- Supporting Information
Bacterial biofilms, a population of bacteria attached to the solid surface, are embedded in a matrix of extracellular polymeric substances (EPS) of bacteria origin to protect the attached growth (Brindle et al., 2011; Flemming and Wingender, 2001). Biofilms are a source of infection and contamination in drinking water supply, medical devices, and food processing environments (Kolter and Greenberg, 2006; Richards and Melander, 2009). Traditional physical/chemical methods such as flushing, chlorination, and UV disinfection are used to control and remove biofilms. However, these methods are often ineffective because bacteria inside the biofilm are more resistant to traditional disinfectants (Srinivasan et al., 2008) and antibiotics (Ito et al., 2009). Many new methods, such as quorum sensing inhibition (Yeon et al., 2009), nitric oxide control (Barraud et al., 2009), and enzymatic disruption (Caro et al., 2009; Leroy et al., 2008), are emerging to control and remove biofilms. The chemical or enzymatic treatments show promising results of targeting biofilm cohesion rather than killing biofilm bacteria (Brindle et al., 2011). Relatively new antimicrobial agents such as lactoferrin and xylitol have demonstrated effective in inhibiting Pseudomonas aeruginosa biofilms (Ammons et al., 2011). A combination of bactericides, enzymes, and antibiotics may have the synergistic effect on improving biofilm control and removal (Ammons et al., 2011; Mikuniya et al., 2007).
Bacteriophage treatment is another emerging method in biofilm control and removal (Azeredo and Sutherland, 2008; Harper and Enright, 2011). A bacteriophage can attach to the host bacterial cell by recognizing specific receptors and injecting its nucleic acids into the host cell. Phage progeny is synthesized inside the host cell, and then lytic phages are released from the host. The phage may penetrate the biofilm to directly infect specific host bacteria or help produce enzymes to degrade EPS that promotes biofilm formation and protect biofilm bacteria (Donlan, 2009; Hanlon et al., 2001). Therefore, phage therapy has the great potential to control biofilm formation (Payne and Jansen, 2001; Weld et al., 2004). For instance, for P. aeruginosa that exhibits multiple mechanisms of antimicrobial resistance and is highly active in biofilm formation (Harper and Enright, 2011), T7-like lytic phages isolated from river water effectively prevented and dispersed the multidrug resistant bacterial strains that were isolated from the hospital environment (Ahiwale et al., 2011). A phage encoding a phage polysaccharide lyase was successful in treating P. aeruginosa biofilms in cystic fibrosis patients by aerosol administration (Sulakvelidze and Pasternack, 2007). Indigenous phages isolated from untreated sewage samples were incorporated into a phage cocktail that could successfully prevent P. aeruginosa biofilm formation on the surfaces of catheters and other indwelling medical devices (Fu et al., 2010).
Phages are abundant in water bodies (Madigan et al., 2009), especially in wastewater. The concentrations of phages in the activated sludge system range from 4.0 × 107 to 3.0 × 109 PFU/mL (Otawa et al., 2007). The numbers of specific phages such as coliphages in wastewater influent are between 1,000 and 10,000 PFU/mL (Yasunori et al., 2002). Since phages isolated from wastewater have broad host ranges with adequate host specificity and infectivity (Hantula et al., 1991; Jensen et al., 1998; Khan et al., 2002), we evaluated the efficiency of bacteriophages isolated from wastewater in P. aeruginosa biofilm control and removal. Furthermore, because chlorination is still the most widely used disinfection process, we determined the effectiveness of a combination of phages and chlorine in biofilm control and removal. P. aeruginosa was selected as a model bacterial host, which is commonly found in chlorinated potable water (Anaissie et al., 2002) and can excrete exopolysaccharides to form biofilms that are resistant to antibiotics and antiseptics (Drenkard and Ausubel, 2002; Dunne, 2002; Mah et al., 2003; Whiteley et al., 2001).