Rapidly inactivate L. monocytogenes biofilm by octenidine hydrochloride.

L. monocytogenes can grow in biofilm attached to a variety of food processing plant surfaces. Its ability to survive in a biofilm on equipment helps it to resist superficial cleaning and disinfection treatments.

Obviously, there is a need for safe and effective antimicrobials to kill L. monocytogenes biofilms. Octenidine hydrochloride (OH) is a cationic surfactant with broad spectrum antimicrobial activity and a low toxicity profile. It was originally developed as an anti-plaque agent in mouthwashes. Scientists at the University of Connecticut investigated its antimicrobial efficacy for eliminating L. monocytogenes biofilms. They found that the compound rapidly inactivates L. monocytogenes in biofilm, and could potentially be used as a sanitizer in processing plants.

In experiments, three strains of L. monocytogenes were grown individually in tryptic soy broth with 0.5% yeast extract overnight at 37 C. They were diluted to a ratio of 1:40 in the broth. Sterile 96-well polystyrene plates were inoculated with 200 ml of cell suspension and incubated without shaking at 37 C or 21 C for 24 hours, or at 4 C for seven days. The biofilms were treated with OH at 0, 10 or 20 mM for 0, 2, 5 and 10 minutes. Their viability was assessed by crystal violet staining and by measuring absorbance at 570 nm.

In addition, after exposure to OH, viable L. monocytogenes counts in each biofilm were determined by plating the samples. Five samples of the treatment and the control were included. The experiment was replicated three times. All concentrations of OH completely killed viable L. monocytogenes in biofilms after five minutes of exposure, compared to the controls. The anti-biofilm activity of OH was concentration-dependent, with 20 mM of OH killing the biofilm immediately on exposure. Results from separate experiments also revealed that adding low OH concentrations, 1 mM and 5 mM, to planktonic cells prevented biofilm formation by L. monocytogenes.

Further information. Thomas Hoagland, Department of Animal Science, University of Connecticut, 3636 Horse Barn Road Ext., Storrs, CT 06269; phone: 860-486-1069; fax: 860-486-4375; email: thomas.hoagland@uconn.edu.

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