Effect of Growth Conditions on Inactivation of Escherichia coli with Monochloramine

Abstract

Reduced susceptibility of bacteria to disinfection is a serious concern in drinking water distribution systems (DWDS), yet the mechanisms and conditions governing reduced susceptibility are not well characterized. The effects of growth temperature, growth rate, and growth mode (suspended growth versus growth in biofilms) on inactivation kinetics of Escherichia coli exposed to monochloramine were studied in order to understand growth conditions that may reduce susceptibility of bacteria to disinfectants in DWDS. Cells grown at a suboptimal temperature (20 degrees C) were significantly less sensitive to monochloramine inactivation (using 0.5 and 5.0 mg/L monochloramine (as Cl2)) than cells grown at an optimal temperature (37 degrees C). Cells grown in biofilms were also significantly less sensitive than cells grown in suspension. No difference in inactivation kinetics was observed for cells grown in monolayer versus multilayer biofilms and between cells grown at different growth rates in chemostat bioreactors. Biofilm cells were estimated to grow at specific growth rates (mu) averaging between mu = 0.08 and 0.13 h(-1), which were approximately within the range of tested suspended growth conditions (mu = 0.04-0.10 h(-1)) using fluorescence in situ hybridizations targeting 16S rRNA. This result indicates that the reduced susceptibility of biofilm cells to monochloramine inactivation is not related to their specific growth rate within the range tested in this study. This work suggests that growth at suboptimal temperatures and growth in biofilms are important factors contributing to reduced susceptibility of bacteria to inactivation with monochloramine.

Roles of ionic strength and biofilm roughness on adhesion kinetics of Escherichia coli onto groundwater biofilm grown on PVC surfaces

“…Biofilms in DWDS were reported to be capable of attracting and harboring pathogens (Berry et al, 2006). In addition, biofilm matrix may prevent disinfectants from reaching the cells located deep inside the biofilm (Berry et al, 2009; Gagnon et al, 2008; Norton et al, 2004; Williams and Braun-Howland, 2003). As a result, pathogenic microorganisms such as Mycobacterium avium and Legionella pneumophila have been found in DWDS biofilms (Falkinham et al, 2001; Le Dantec et al, 2002; Torvinen et al, 2004; Declerck et al, 2009; Lau and Ashbolt, 2009; Valster et al, 2011; Wullings et al, 2011).…”

Chlorine Tolerance and Inactivation of Escherichia coli recovered from Wastewater Treatment Plants in the Eastern Cape, South Africa

“…The coefficient of dilution, n values were 4.66, 5.07 and 4.67 for E. coli SAMRC-1, E. coli SAMRC-2 and E. coli SAMRC-3, respectively. Differences in n represent the average number of disinfectant molecules in contact with an organism available to cause inactivation [58] and this was reflected in the increased inactivation for E. coli SAMRC-2 (higher value of n = 5.07) compared to the other E. coli strains. Variations in n indicate physiological differences between organisms, inactivation conditions and availability of nutrients in the cultivation media [58].…”

“…Differences in n represent the average number of disinfectant molecules in contact with an organism available to cause inactivation [58] and this was reflected in the increased inactivation for E. coli SAMRC-2 (higher value of n = 5.07) compared to the other E. coli strains. Variations in n indicate physiological differences between organisms, inactivation conditions and availability of nutrients in the cultivation media [58]. Difference in the values of k and n for two strains of E. coli, K12 and 0157:H7 exposed to chlorine concentrations of 0.1-8.0 mg/L for 10 min have been reported [59].…”

Proteomic adaptations to starvation prepare Escherichia coli for disinfection tolerance

“…The Chick-Watson inactivation model was used to simulate the inactivation profile of monochloramine (Berry et al 2008) $$\text{italicln}true(\frac{N}{N_0}true)=true\{\begin{array}{cc}left1& leftif{C}^{n}t<C^n{t}_{\text{italicSHOULDER}}\\ left-k(C^{n}t-C^n{t}_{\text{italicLAG}})& leftif{C}^{n}t>C^n{t}_{\text{italicSHOULDER}}\end{array}true\}$$ N and N 0 are cell counts at time t and time zero, k is the inactivation rate constant, t SHOULDER is the shoulder phase, n is an empirical parameter that describes the relative importance of the concentration of disinfectant which was set as 1 in this study, C is the disinfectant concentration, and t is inactivation time. T-test was used to determine if the k values between normal and starved cells was significantly different ( p <0.05) in the monochloramine experiments.…”