Abstract
Microbial resistance to antimicrobial agents continues to be a major problem. The frequent use and misuse of disinfectants based on quaternary ammonium compounds (QACs) in food-processing industries have
imposed a selective pressure and may contribute to the emergence of disinfectant-resistant microorganisms. A total number of 1,325 Gram-negative isolates (
Escherichia coli
, other coliforms
Vibrio
spp., and
Aeromonas
spp.) and 500
Enterococcus
spp. from food and food-processing industries and fish farming were screened for natural resistance to the QAC-based disinfectant benzalkonium
chloride (BC). Of the 1,825 isolates, 16 strains, mainly from meat retail shops, showed low-level resistance to BC. None of the
Enterococcus
spp. from broiler, cattle, and pigs, the antibiotic-resistant
E. coli
from pig intestine and fish pathogens
Vibrio
spp. and
Aeromonas
spp. from the Norwegian fish farming industry were resistant to BC. The BC-resistant strains were examined for
susceptibility to 15 different antibiotics, disinfectants, and dyes. No systematic cross-resistance between BC and any of the other antimicrobial agents tested was detected. Stable enhanced resistance in
Enterobacter cloacae
isolates was demonstrated by step-wise adaptation in increasing concentrations of BC. In conclusion, BC resistance among food-associated Gram-negative bacteria and
Enterococcus
spp. is not frequent, but resistance may develop to user concentrations after exposure to sublethal concentrations of BC.