LEON, SpainNew research published ahead of print in the journal Applied and Environmental Microbiology suggests the improper use of biocides at sublethal doses in food production may endanger public health by increasing antibiotic resistance in bacteria and enhancing their ability to form harmful biofilms.

Biofilms boost the risk of food contamination by providing a reservoir of microorganisms, and biofilm formation is a major virulence factor in human infections. Biofilm formation also boosts operation and maintenance costs in food production by interfering with heat exchangers, plugging filters and blocking tubes in water distribution systems.

Researchers at the University of Leon investigated whether exposing Escherichia coli bacteria to sub-lethal concentrations of each of three food-grade biocides could result in greater antibiotic resistance, a greater ability to form damaging and potentially virulent biofilms and to survive normally lethal doses of biocides.

Exposures to the biocide sodium nitrite increased resistance to 14 out of 29 antibiotics tested. E. coli cells also acquired tolerance to the biocides, especially sodium nitrite and sodium hypochlorite, and the two biocides improved the microbes' ability to form biofilms. Conversely, exposure to the biocide trisodium phosphate reduced E. coli's ability to form biofilms, and boosted resistance only to a single antibiotic.

"These findings are in agreement with reports of other authors, where adaptation of E. coli to both chemical and physical sublethal stresses has been demonstrated," the researchers said. "The increased tolerance observed suggests that the use in food environments of compounds which when used inappropriately may provide sublethal exposure represents a real risk for the development of adaptation to biocides."

"Recent scientific evidence suggests that the selective pressure exerted by the use of biocides at sub-lethal concentrations could contribute to the expression and dissemination of antibiotic resistance mechanisms," said corresponding author Rosa Capita.