Biofilms can be problematic to swine drinking water systems as they can harbor pathogens, decrease water quality, and may contribute to antimicrobial treatment failure. Water-administered antimicrobials are used for disease treatment in swine populations, yet, little is known about water line ecology and the impact it can have on antimicrobial resistance and stewardship. Water line cleaning and disinfection may aid in removal of water line biofilms, improve swine health, and antimicrobial stewardship. Water line samples were collected pre-treatment (0), 24 h post-treatment with 0.78% CID 2000 Pro (peracetic acid) (1), and 3, 5, 7, 14, 21, 42, 56, and 77-days post-treatment from six wean-to-finish swine farms in Iowa, USA. Biofilm was aseptically extracted from the interior of the water line pipe ( n = 119) and submitted for metagenomic analysis to detect antimicrobial resistance genes (ARGs). This study demonstrates high prevalence of ARGs in swine water line biofilms that could confer resistance to both medically important antimicrobials to humans and animals such as aminoglycosides, beta-lactams, fluoroquinolones, colistin, and fosfomycin. From 115 samples, a frequency of 3,904 ARGs were reported, with 184 unique ARGs defined. Four samples contained no ARGs. One hundred and fifty-one integron genes representing three classes were found in 115 of 119 samples, indicating mechanisms of potential spread of multiple drug resistance. ARGs and integron genes combined were significantly lower on average by 10 unique ARGs/ integron genes 24-h post-treatment (1) when compared to pre-treatment (0) counts ( p -value = 0.01). The number of unique ARG and integron genes quickly rebounded and were not statistically significant compared to pre-treatment counts on post-treatment dates 3, 5, and 7 (adjusted p -value ≥ 0.05), and by post-treatment date 14, unique ARG and integron genes were significantly higher than pre-treatment (adjusted p -value = 0.012). This study demonstrates that swine water line biofilms can harbor antimicrobial resistance genes which could have potential clinical impacts on pig health and treatment response.
Doughan et al. (Wed,) studied this question.