Effect of pipe material on the development of biofilms in drinking water distribution systems

CORIMAYO SHEILA; RAJAL, VERONICA; CRUZ, MERCEDES CECILIA

Congreso; Congreso Conjunto de la Sociedad Argentina de Investigación Bioquímica (SAIB) y la Asociación Civil de Microbiología General (SAMIGE; 2021

Biofilms developed on the inner-walls of drinking water pipes account for the 95% of microbial mass in these systems. They are considered a health risk as they could become a reservoir of pathogens and influence water quality stability. The pipe material is one of the main factors that determine biofilm attachment and further formation and development. Despite the water alteration they can produce, these biofilms are poorly studied due to limited access to actual pipes. The aim of this work wasto evaluate the effect of pipe material on the formation of biofilms in the DWDS, using a new-designed and easy to handle coupon system, and their importance as reservoir of pathogenic organisms in the drinking water microbiome. Coupons of 15 mm diameter and 2 mm thickness were built with materials commonly used in DWDS: PVC (polyvinyl chloride), PP (polypropylene) and Cem (cement). These coupons were sterilized and incubated in a concrete cistern (196350 L), exposed to natural conditions for 7 months: March-October (7M) and 11 months: March-February (11M). Biofilm samples grown on the coupon surface were detached using sonication and vortex in 5 mL PBS 1×. From that elution, the number of culturable organisms was compared using: Agar Plate Count (APC) at 37 °C and Reasoner 2A (R2A) agar at 21 °C. An enriched biofilm elution was used to determine the presence of pathogenic and/or opportunistic organisms: Escherichia coli (mTEC), Pseudomonas aeruginosa (Cetrimide), Salmonella spp. (SS agar). The samples incubated for 7M, showed statistically significant differences in the number of cells grown on APC between the pipe materials (p-value = 0.001). It was higher inCem (2.8 x 103 CFU/cm2) compared to PVC (1.3 CFU/cm2) and PP (21.4 CFU/cm2). In contrast, on R2A plates no significant differences were found between the materials (p-value > 0.05). The 11M samples showed significant differences in bacteria count on both media. On APC, colony count was higher on PP (8.3 CFU/cm2) compared to Cem (2.3 CFU/cm2) and nongrowth was observed on PVC (p-value = 0.02). On R2A, the colony number was higher in Cem (117.5 CFU/cm2) followed by PVC (27.5 CFU/cm2) and PP (6.03 CFU/cm2). A higher cell counting was observed on R2A in 7M compared to 11M (p-value= 0.003); whereas there was no difference of bacteria count on APC for both time periods (p-value > 0.05). Samples 7M and 11M showed presence of organisms on Cetrimide and SS agars on both PVC and Cem. On PP, growth was only observed on Cetrimide in the 7M samples. Surprisingly, the higher abundance of microorganisms was found in the 7M samples. These results could be due to the exposure to actual environmental factors, such as increased disinfectant effect in the 11M period. The growth of organisms in the specific medium indicates presence of pathogenic and/or opportunistic microorganisms in these biofilms.