Characterization of Serratia marcescens surviving in disinfecting footbaths

To determine if disinfecting footbaths in the food industry were contaminated with bacteria and to characterize some of the bacteria present.Bacterial strains were isolated from disinfecting footbaths containing TEGO 103G (amphoteric disinfectant) or TP-99 (alkyl amino acetate-based disinfectant) in five of six dairy factories. Fourteen strains identified as Cedecea spp. by their fatty acid composition were further characterized. Results from Rapid ID 32 E API analysis and 16S-rDNA-sequencing showed that all strains were Serratia marcescens. Unlike S. marcescens ATCC 13880, the isolates from disinfecting footbaths were not killed (<5 log10 reduction) by the recommended in-use concentration of TEGO 103G, TEGO 51 or benzalkonium chloride. Survival and multiplication in tap water with an in-use concentration of TEGO 103G was demonstrated for one of the strains. All strains were killed by the in-use concentrations of commercial disinfectants based on peracetic acid, hypochlorite, quaternary ammonium compounds and alkyl amino acetate (TP-99). There were no indications of cross-resistance between disinfectants and antibiotics.Serratia marcescens may survive and multiply in disinfecting footbaths containing TEGO 103G or alkyl amino acetate because of disinfectant resistance.Disinfecting footbaths may act as contamination sources in food factories and should not be used without regular hygienic monitoring.