Disinfectant and antibiotic resistance of lactic acid bacteria isolated from the food industry

Quaternary ammonium compounds (QACs) are widely used as disinfectant in med ical and food environments. There is a growing concern about the increasing incidence of disinfectant-resistant microorganisms from food. Disinfectant -resistant lactic acid bacteria (LAB) may survive disinfection and cause sp oilage problems. Moreover, resistant LAB may potentially act as a reservoir for resistance genes. A total number of 320 LAB from food industry and mea t were screened for resistance to the QAC benzalkonium chloride (BC). Out o f 320 strains, five strains (1.5%) were considered to be resistant and 56 ( 17.5%) were tolerant to BC, The resistant strains were isolated from food p rocessing equipment after disinfection. The resistant, tolerant, and some s ensitive control bacteria were examined for susceptibility to 18 different antibiotics, disinfectants, and dyes using disc agar diffusion test and mic rodilution method. Little systematic cross-resistance between BC and any of the antimicrobial agents tested were detected except for gentamycin and ch lorhexidine, A BC-tolerant strain was much easier to adapt to higher levels of BC as compared to a BC-sensitive strain. No known Gram-positive QAC res istance genes (qacA/B, qacC, qacG, and qacH) were detected in the BC-resist ant strains. Identification to species level of the BC-resistant isolates w as carried out by comparative analysis of 16S-rDNA sequencing. In conclusio n, resistance to BC is not frequent in LAB isolated from food and food envi ronments. Resistance may occur after exposure to BC, The BC resistant isola tes showed no cross-resistance with other antimicrobial compounds, except f or gentamycin and chlorhexidine, Nevertheless, BC-resistant LAB may be isol ated after disinfection and may contribute to the dissemination of resistan ce.