Efficacy of peracetic acid and chlorine in managing <i>Salmonella</i> biofilms in irrigation loop systems

Biofouling presents significant challenges to the crop production industry, notably reducing irrigation efficiency and potentially dispersing pathogens to irrigated crops. This study evaluated the efficacy of peracetic acid (PAA) and chlorine (Cl) against <i>Salmonella</i> biofilms in irrigation lines with or without fertilizers. Pond water (PW) with 2-4-1 fish emulsion (O), PW with 4-0-8 synthetic liquid fertilizer (S), or PW with no fertilizer (NoFert) was inoculated with 2 log CFU/mL of a rifampicin-resistant <i>Salmonella</i> cocktail. Inoculated water was then circulated through polyethylene loop irrigation system for a month. <i>Salmonella</i> populations both in the water and attached to the tubing were determined. Data showed that a single point of contamination from the water resulted in a biofilm formation with O and NoFert, but not the S treatments, after 3 days. Both PAA and Cl effectively reduced <i>Salmonella</i> populations for all fertilizer treatments in water samples. However, when no sanitizer was introduced to the line, bacterial dispersion resulted in the contamination of a subsequent irrigation event for the O treatments but not the S and NoFert treatments, which presented no microbial proliferation. Our findings suggest that O treatments resulted in persistent biofilm formation that could lead to contamination of irrigation water when no sanitizers are introduced. These studies provide insight into the behavior of foodborne pathogens in irrigation distribution systems.IMPORTANCEThe accumulation of bacteria in water distribution systems due to biofouling can lead to contamination, making it crucial to evaluate and implement effective mitigation measures to prevent these issues and ensure safe and efficient irrigation practices. The use of the 2-4-1 fish emulsion in-line may support the establishment of <i>Salmonella</i> biofilms and subsequent cross-contamination of irrigation water if not fully flushed from the system. This study demonstrates that PAA and Cl effectively reduce <i>Salmonella</i> contamination in water but will not eliminate populations in-line once biofilms are established.