Disinfectant tolerance and biofilm formation of bacteria isolated from drinking water distribution systems
Ng, Li Hui
Date of Issue2017-12-21
School of Civil and Environmental Engineering
Many microorganisms inhabit drinking water distribution systems and these microorganisms could deteriorate the quality of the water due to unrestrained microbial activities. These microorganisms form biofilms, even in the presence of disinfectants. The biofilm samples were first isolated and identified through a series of methods to determine the isolates from drinking water. To further study the microorganisms, five isolates that are significant in the drinking water systems were selected for biofilm formation analysis in both R2A and LB media to compare the growth of bacteria under different conditions. Furthermore, these five isolates were also exposed to 2 mg/L and 4 mg/L of monochloramine as Cl2 concentrations to study their tolerance against the disinfectant. The results showed that Pseudomonas aeruginosa (15GP) and Pseudomonas stutzeri (16CW) formed at least 10 times more biofilms than the remaining three isolates as they are heterotrophic bacteria which take in organic carbon for their growth and grew faster in the media tested. While Mycobacterium sp. (16LO) formed the least number of biofilms most likely due to the bacteria being isolated and identified in this study exists as a slow-grower. In addition, dual-species biofilm formation on Gordonia sp. (08LO) and Methylobacterium sp. (PB1510) was also analysed. The results showed the growth of Gordonia sp. (08LO) was inhibited by Methylobacterium sp. (PB1510) in LB medium; however, the growth of Gordonia sp. (08LO) promotes the formation of biofilms of Methylobacterium sp. (PB1510) in R2A medium. In monochloramine tolerance analysis, the results showed that Mycobacterium sp. (16LO) is the most resistant bacteria due to the impermeability of the cell wall that restrict monochloramine from entering the cell. On the other hand, Pseudomonas aeruginosa (15GP) were not tolerance against monochloramine as all the bacteria were killed in 60 minutes. However, this result differed from many studies, probably due to the Pseudomonas aeruginosa (15GP) that were isolated and identified in this study exist in a viable but non-culturable state during the tested incubation period. Alternatively, the reduction in the number of bacterial cells of Pseudomonas aeruginosa (15GP) could possibly happen only in planktonic phase. Further analysis is needed to verify if Pseudomonas aeruginosa (15GP) is tolerance against monochloramine in the biofilm phase.
Final Year Project (FYP)
Nanyang Technological University