Abstract
Listeria monocytogenes is a one of the most important food-borne pathogens. Its ability to form biofilm contributes to increased resistance to disinfectants and inefficient disinfection, posing a serious threat for the food industry, and in the end the consumer. The aim of this study was the comparison of the biofilm formation ability of L. monocytogenes strains on stainless steel, under different environmental conditions (temperature, pH, NaCl concentration, nutrients availability), and the assessment of biofilm susceptibility to disinfectants. The bactericidal activity of four disinfectants in two concentrations (100% and 50% of working solution) against biofilm was conducted on four clinical strains, four strains isolated from food and one reference strain ATCC 19111. It was found that biofilm susceptibility to disinfectants was influenced by environmental conditions. Biofilm susceptibility correlated with the decrease of temperature, pH, nutrients availability and salinity of the environment. The least sensitive to disinfectants was biofilm produced at pH = 4 (the bacterial number ranged from 0.25 log CFU × cm−2 to 1.72 log CFU × cm−2) whereas the most sensitive was biofilm produced at pH = 9 (5.16 log CFU × cm−2 to 7.84 log CFU × cm−2). Quatosept was the most effective disinfectant, regardless of the conditions. In conclusion, biofilm susceptibility to disinfectants is strain-dependent and is affected by environmental conditions.
Highlights
Listeria monocytogenes is a Gram-positive, non-spore forming, rod-shaped bacterium, widespread in the environment
It was found that biofilm formation ability, to a certain extent, was strain-dependent and was affected by environmental conditions
Statistical analysis showed that the number of bacteria recovered from the biofilm was not dependent on the strain, and that the differences found in the number of bacteria recovered from the biofilm resulting from different environmental conditions for individual L. monocytogenes strains tested were not statistically significant (Table 1)
Summary
Listeria monocytogenes is a Gram-positive, non-spore forming, rod-shaped bacterium, widespread in the environment. One of the major causes of food contamination with L. monocytogenes is its ability to form biofilm and to survive under adverse environmental conditions [4,5]. Bacteria of the Listeria genus are capable of producing biofilm on various surfaces, including polypropylene, stainless steel and glass. The multilayered structure of biofilm facilitates access to nutrients and the removal of metabolites, while it hinders access of biocides to deeper biofilm layers [8]. Bacteria in such a community are much more resistant to stress conditions, antimicrobials and disinfectants compared with the planktonic cells [9]. Bacteria in these niches are protected against cleaning and disinfection [10]
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