Impedimetric determination of activity of disinfectants and detergents on Listeria: preliminary study

The Elimination of Listeria Monocytogenes Attached to Stainless Steel or Aluminum Using Multiple Hurdles

Ready-to-eat luncheon meats sliced in retail delis have been found to pose the greatest risk of foodborne illness from Listeria monocytogenes among all ready-to-eat foods. Slicers used in delis have many removable parts that are connected with seals and gaskets, with spaces, cracks and crevices that are difficult to clean adequately and may provide a niche for L. monocytogenes survival. Standard cleaning and sanitizing practices used by deli employees may not eliminate Listeria in these niches. Moist heat is known to be more effective against L. monocytogenes than dry heat at the same temperature and time. The study reported here investigated the effects of moist heat combined with quaternary ammonium compounds (5 or 10 ppm), chlorine (10 or 25 ppm) or peracetic acid (10 or 25 ppm) on inactivating L. monocytogenes attached to stainless steel or aluminum coupons cut from commercial deli meat slicer components. All sanitizers when used alone resulted in a 2- to 3-log reduction of L. monocytogenes on stainless steel or aluminum surfaces, while moist heat alone resulted in a 3- to 4-log reduction. When combined with heat the quaternary ammonium was used at 5 ppm, peracetic acid at 10 ppm and chlorine at 10 ppm. When the 2 lethal treatments were combined there was a 5- to7-log reduction as compared to initial inoculation.

PRACTICAL APPLICATION

The results of this study will provide a better understanding and potential methods for the sanitization of industrial deli meat slicers. In turn, the knowledge gained from this study can reduce the risk of contamination and outbreaks of L. monocytogenes and other food-borne pathogens for consumers.

Chlorine resistance of Listeria monocytogenes biofilms and relationship to subtype, cell density, and planktonic cell chlorine resistance

Strains of Listeria monocytogenes vary in their ability to produce biofilms. This research determined if cell density, planktonic chlorine resistance, or subtype are associated with the resistance of L. monocytogenes biofilms to chlorine. Thirteen strains of L. monocytogenes were selected for this research based on biofilm accumulation on stainless steel and rep-PCR subtyping. These strains were challenged with chlorine to determine the resistance of individual strains of L. monocytogenes. Planktonic cells were exposed to 20 to 80 ppm sodium hypochlorite in 20 ppm increments for 5 min in triplicate per replication, and the experiment was replicated three times. The number of tubes with surviving L. monocytogenes was recorded for each isolate at each level of chlorine. Biofilms of each strain were grown on stainless steel coupons. The biofilms were exposed 60 ppm of sodium hypochlorite. When in planktonic culture, four strains were able to survive exposure to 40 ppm of chlorine, whereas four strains were able to survive 80 ppm of chlorine in at least one of three tubes. The remaining five strains survived exposure to 60 ppm of chlorine. Biofilms of 11 strains survived exposure to 60 ppm of chlorine. No association of biofilm chlorine resistance and planktonic chlorine resistance was observed; however, biofilm chorine resistance was similar for strains of the same subtype. Biofilm cell density was not associated with chlorine resistance. In addition, biofilms that survived chlorine treatment exhibited different biofilm morphologies. These data suggest that chlorine resistance mechanisms of planktonic cells and biofilms differ, with planktonic chlorine resistance being more affected by inducible traits, and biofilm chlorine resistance being more affected by traits not determined in this study.

Differences in the sensitivity to eight disinfectants of Listeria monocytogenes strains as related to their origin (short note)

The efficacy of eight commercialized disinfectants proposed by several manufacturers was evaluated using the French standard in the presence of organic matter and against Listeria monocytogenes and L. innocua strains isolated in a dairy plant, against other Listeria strains of various origin and reference strains of Staphylococcus aureus and Enterococcus faecium. Products containing quaternary ammonium plus peroxide or amine were shown to be efficient at the concentrations recommended by the manufacturer. Differences in sensitivities were noticed for one disinfectant containing chlorine.

Efficiency of sanitizing agents for destroying Listeria monocytogenes on contaminated surfaces

In an effort to control the potential hazard of dairy product contamination by contact with processing surfaces, the efficiency of four commercial sanitizing agents was evaluated using the AOAC use-dilution method for their bactericidal activity at 4 and 20 degrees C against Listeria monocytogenes strain Scott-A attached on four types of surfaces (stainless steel, glass, polypropylene, and rubber). Our results indicate that all sanitizers tested were more efficient against L. monocytogenes attached to nonporous surfaces than to porous surfaces. After 10 min of contact time, the limit concentration of disinfectants was at least 5 to 10 times higher for sanitizing rubber than stainless steel or glass surfaces. Concentrations of each sanitizer needed to be higher at sanitation at 4 degrees C than at 20 degrees C to destroy L. monocytogenes attached to stainless steel, glass and rubber when surface contamination was achieved at 4 or 20 degrees C.