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The aim of this study was to characterize the role of biocide interventions in the emergence of
biocide-tolerant Salmonella, its co-selective association with multidrug-resistant Salmonella and
the association with carriage of specific efflux gene markers. Salmonella isolates were detected
in 13.9% (208/1,497) and 6.7% (98/1,468) of swine barn drag swab samples at pre- and post-
disinfection with biocide, whereas, Salmonella isolates were detected in 17.2% (1,180/6,842)
and 7.1% (431/6,093) of the early and late finishing pigs, respectively. Barn-level prevalence of
antimicrobial resistance among Salmonella isolates recovered from the floor swab samples was
92.3% (1,503 of 1,628), whereas, the barn-level prevalence of antimicrobial resistance among
Salmonella isolates recovered from the fecal samples was 98.02% (4,415 of 4,504). A total of
348 Salmonella isolates from swine barns formerly disinfected with Biosentry and 428 from
swine barns disinfected with Synergize were subjected to minimum inhibitory concentration
(MIC) testing for Biosentry and Synergize, respectively. In addition, selected Salmonella isolates
were also genotyped to identify the carriage of quaternary ammonium compound (qac) tolerance
genes. Interestingly, 22.9% (98 of 428) of Salmonella isolates from swine barns disinfected with
Synergize carried the qac gene and the 86% of isolates that carried the qac gene also carried
attenuated qacEΔ1. Nearly 31% (109 of 348) of Salmonella isolates from swine barns disinfected
with Biosentry carried the qac gene. Furthermore, out of 109 Salmonella isolates that carried qac
genes, 94.5% of the isolates contained attenuated qacEΔ1 gene, whereas 72.5% of the isolates
carrying qacEΔ1 gene also carried class 1 integrons which is associated with both antibiotic and
quaternary ammonium compound resistance. Although biocides are effective in limiting the
growth, load and the colonization of bacterial pathogens, this study underscores the contribution
of biocides in selective pressure towards antibiotic resistant in Salmonella. |
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