Listeria organism resilient, deadly

Slime armour | The organism forms a film on gloves, meat slicers, and other food utensils

TORONTO — Listeria is a nasty, dangerous bug that can be found almost everywhere.

“(It) is a very dangerous pathogen,” said food safety microbiologist Dale Grinstead of Sealed Air Corp., a Wisconsin based company that makes protective packaging materials for food, medical equipment and other specialized systems.

“It is ubiquitous. This organism is everywhere.”

Grinstead told a Canadian Meat Council sponsored food safety symposium in Toronto Oct. 2-4 that listeriosis is not as common as salmonella or campylobacter infections, but it can kill up to a quarter of stricken patients.

It is most dangerous to immuno-suppressed, young and elderly people as well as pregnant women, in whom it can cause miscarriage.

It can get past the immune system and travel to the brain and heart and lead to septicemia, encephalitis and endocarditis.

It is also tough and can handle cold and heat, high salt concentrations and rigorous cleaning regimes. Listeria can survive at 1 C.

“Refrigeration is ordinarily a very effective tool in our food safety set of things we can do,” he said. “The vast majority of pathogens can’t grow at refrigerated temperatures.”

More than 20 species of mammals and 20 species of birds can shed the bacteria in their feces. As well, some people may be asymptomatic carriers and don’t realize they are passing it on.

The disease can be present in raw milk and food made from raw milk. It can also live in food processing plants and contaminate a variety of processed meat.

A Perdue University study of grocery stores found it in many places, including cold rooms, drains, floors, cleaning tools and food contact surfaces.

“In a number of cases, these strains were persistent,” Grinstead said.

Floor drains capture a lot of bacteria, but workers may often skip cleaning the drain regularly because no one likes to do it. Their cleaning tools can also become a source of contamination.

Listeria protects itself by creating a biofilm, which is a kind of slime that acts like armour. The biofilm will grow on meat slicers, tools, gloves, packing equipment and motors.

“These biofilms are throughout our operations,” he said.

Rigorous cleaning will remove biofilm in a series of steps that Grinstead calls TACT: time (cleaning longer), action (scrubbing harder), chemical concentrations and temperature.

Sanitizers are often used, but they may not work because they do not get past the biofilm.

“Sanitizers are not useless, but they cannot do the job alone,” Grinstead said. “Sometimes the most effective cleaning chemical is elbow grease.… A little bit of scrubbing is an effective cleaner.”

He said a neutral cleaner such as dish detergent or shampoo with longer cleaning action also removes biofilm.

Some establishments use high-pressure sprays, but it is easy to create aerosols and move micro-organisms where they are not wanted.

Potent chemicals are available for cleaning, but it is important to follow manufacturer’s instructions because more is not better. Don’t bump it up to a 10 percent mix if a one percent solution is recommended,.

Higher temperature will help clean better, but too much hot can cook the biofilm to the surface.

  • Ready-to-eat deli meats and hot dogs
  • Refrigerated pâtés or meat spreads
  • Unpasteurized (raw) milk or dairy products, soft cheese made with unpasteurized milk, such as queso fresco, feta, brie and camembert
  • Refrigerated smoked seafood
  • Raw sprouts
  • Three to 70 days
  • Fever, stiff neck, confusion, weakness, vomiting, sometimes preceded by diarrhea
  • Illness may last days to weeks
  • Older adults
  • Pregnant women
  • People with weakened immune systems.
  • Organ transplant patients who take anti-rejection drugs
  • People with diseases such as HIV/AIDS or other autoimmune diseases, cancer, end-stage renal disease, liver disease, alcoholism and diabetes.
  • Consult a doctor immediately if you are extremely ill with fever or stiff neck.
  • Antibiotics given promptly can cure the infection and, in pregnant women, prevent infection of the fetus.
  • Do not drink raw (unpasteurized) milk and do not eat food that contains unpasteurized milk.
  • Wash hands, knives, countertops and cutting boards after handling and preparing uncooked foods.
  • Rinse raw produce thoroughly under running tap water before eating.
  • Keep uncooked meats, poultry and seafood separate from vegetables, fruit, cooked food and ready-to-eat food.
  • Thoroughly cook raw food from animal sources, such as meat, poultry or seafood, to a safe internal temperature.
  • Wash hands, knives, countertops and cutting boards after handling and preparing uncooked food.
  • Consume perishable and ready-to-eat food as soon as possible.
  • People in higher risk groups should heat hot dogs, cold cuts and deli meat before eating them.

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