Sticking around: Persistent and transient L. monocytogenes strains from retail deli environments

Based on recent risk assessments, up to 83% of listeriosis cases from deli meat in the United States are predicted to be from ready-to-eat deli meats contaminated during processing at retail grocery stores.

listeria.deli.slicer.jan.15Listeria monocytogenes is known to use sanitizer tolerance and biofilm formation to survive, but interplay of these mechanisms along with virulence potential and persistence mechanisms specific to deli environments had yet to be elucidated.

In this study, 442 isolates from food and nonfood contact surfaces in 30 retail delis over 9 months were tested for inlA premature stop codons (PMSCs); inlA encodes InlA, which is necessary to cause listeriosis. A total of 96 isolates, composed of 23 persistent and 73 transient strains, were tested for adhesion and biofilm-forming ability and sanitizer tolerance. Only 10/442 isolates had inlA PMSCs (p<0.001). Strains with PMSCs were not persistent, even in delis with other persistent strains. Most (7/10) PMSC-containing isolates were collected from food contact surfaces (p<0.001); 6/10 PMSC-containing isolates were found in moderate prevalence delis (p<0.05). Persistent strains had enhanced adhesion on day 1 of a 5-day adhesion-biofilm formation assay. However, there was no significant difference in sanitizer tolerance between persistent and transient strains.

Results suggest that foods contaminated with persistent L. monocytogenes strains from the retail environment are (1) likely to have wild-type virulence potential and (2) may persist due to increased adhesion and biofilm formation capacity rather than sanitizer tolerance, thus posing a significant public health risk.

 Persistent and transient Listeria monocytogenes strains from retail deli environments vary in their ability to adhere and form biofilms and rarely have inlA premature stop codons

Foodborne Pathogens and Disease [ahead of print]

Wang Jingjin, Ray Andrea J., Hammons Susan R., and Oliver Haley F.

http://online.liebertpub.com/doi/abs/10.1089/fpd.2014.1837

Slimer in the Kitchen: Salmonella biofilm means more work when using disinfectants

Who you gonna call? GHOSTBUSTERS! Or – a professional cleaning company.

My favorite character from the Ghostbusters series is Slimer, mainly because he always seems to get away with causing chaos around him. As a kid, I didn’t think too much about his puke-green color or possible germs that he might be carrying. However, after reading an article from the Norwegian School of Veterinary Medicine about Salmonella biofilms, I’ve come to the conclusion that Slimer was probably a giant lump of Salmonella coated in a protective biofilm.  Bacteria have multiple forms of defense, and some bacteria are able to produce a biofilm, or a slimy outer covering, in order to protect itself from disinfectants and to ensure its survival in the environment.  Too bad the Ghostbusters guns didn’t have alcohol and Virkon in them, otherwise Slimer would be toast.
 
In her doctoral thesis, Lene Karine Vestby studied why it is so difficult to get rid of once they have managed to establish themselves in Norwegian feed and fish meal factories. She discovered that bacteria efficient at forming biofilm (bacteria coating) survived for longer in the factories than those that had a reduced ability to form this coating. The ability to survive in factories therefore appears to be connected with the ability to form a biofilm and it would seem that removing biofilm is a necessary step towards eradicating from the factories.
 
Vestby studied the effect of nine most frequently used disinfectants and found that their efficiency is substantially reduced of the Salmonella has managed to form a biofilm. The effect of the majority of the disinfectants was then no longer satisfactory, but a product containing 70% ethanol was the most efficient, followed by one called Virkon S. These results could improve the efficiency of the cleaning procedures used by processing plants in the animal feed industry, and also in the human food industry.
 
Of course it’s not just about finding the right tools, the tools must be properly used. Proper production methods should be in place to prevent the contamination of the feed. Processing and packaging facilities should follow a regular cleaning schedule with the appropriate disinfectants. These things all contribute to the culture of food safety. They should also keep Slimer out of the kitchen.