Back to basics...

Meeting with the microbes

Part 3

Welcome to the third article in this series: This month’s exclusive “autobacteriography” is with Mr. Listeria monocytogenes, aka L.mono by those who have been previously introduced.

Brace yourself..... you are becoming microscopic..... Honey, I shrunk the readers begins!

PART 3: Listeria (L.) monocytogenes

The Food Safety Network (TFSN) Reporter: Good day and welcome Mr. L mono to The Food Safety Network. We are very fortunate to have you here, live and exclusive on our website.

Mr L. monocytogenes: I believe the pleasure is all mine. Your previous interviewees and close friends, Mr. S.aureus and Mrs. E.coli, have only praise for your show.

TFSN Reporter: Oh excellent! The fact that the readers and myself are on your microscopic level during this interview make us appreciate your “culture”....  Let’s begin with your full name...

Mr L. monocytogenes: Listeria monocytogenes: I belong to the genus Listeria and am very closely related to the Clostridium sub-branch, together with Staphylococcus.  My genus is made up of six species, but I am the only one that is associated with illness in mankind.

TFSN Reporter: Indeed, you are the captain of your genus. Tell us a bit more about how your relationship to Mr Murray.

Mr L. monocytogenes: Who?....Oh yes the man that discovered me! In 1926, E.G.D. Murray, after six cases of death in his rabbits, first described my existence.  

TFSN Reporter: You were first named Bacterium monocytogenes?.

Mr L. monocytogenes: Very impressive. My name was changed to Listeria monocytogenes by Harvey Pirie in 1940. But I only made headlines a few decades later in 1981, when I was identified as the cause of foodborne illness: I resulted in 41 cases and 18 deaths, mostly in pregnant woman and neonates in Halifax, Nova Scotia, after they consumed coleslaw containing cabbage that had been treated with raw sheep manure.


TFSN Reporter: That’s, no offense meant, quite are quite the killer then?

Mr L. monocytogenes: Yes, amongst my peers I am known as the baby killer. But I am just a gram-positive, rod-shaped bacterium and move from place to place though a distinctive tumbling motion.

TFSN Reporter: Why the baby-killer? And from what I have read you result in a 20-30% death rate amongst whom you infect, which exceeds the fatality rates of Salmonella and Clostridium bolulinum?

Mr L. Monocytogenes: My target population for causing disease as we call it, listeriosis, is pregnant women/fetus, where I induce perinatal or neonatal infections.

TFSN Reporter: What is listeriosis and why pregnant woman?

Mr L. monocytogenes:  Listeriosis is the infection I cause. I manifest septicemia, meningitis, encephalitis and other intrauterine or cervical infection in pregnant women, which may result in the spontaneous abortion during the 2nd or 3rd trimester or stillbirth. I can also infect normal healthy individuals should they overuse antacids or cimetidine.

TFSN Reporter: Of the three bacterium I have now interviewed, you take the cake for the most dangerous? How does a person know that you have infected them?

Mr L. monocytogenes: Actually I am in the cake – well the dairy cream icing to be precise. I firstly give rise to flu-like symptoms – including a persistent fever. Nausea and vomiting may also be induced if my infection is more serious.

TFSN Reporter: So you are a fan of dairy products? How did you get into them in the first place?

Mr L. monocytogenes: Well this is my trade secret of success.  If I tell you, you may use it against me and my species.  I love foods such a raw milk, supposedly pasteurized fluid milk, cheeses (soft-ripened types like Brie, Camembert and Feta), ice-cream, raw vegetables, fermented raw-meat sausages, raw and cooked poultry, raw meats, and raw and smoked fish.

TFSN Reporter: I seem to see an underlying trend here....all foods that need refrigeration?

Mr L. monocytogenes: You are quite observant, yes, but not limited to!  I am able to grow at temperatures as low as 0°C and thus will multiply in your fridges and in the foods I inhabit.  

TFSN Reporter: But how did you manage to contaminate the food in the first place?

Mr L. monocytogenes: Well I get around quite a bit: I am found in at least 37 mammalian species, feral and domesticated, 17 species of birds and even some of our fish and shellfish friends. I can also inhabit soil and silage, just to mention a few environmental sources. Thus I am a hardly bug and resistant to the deleterious effects of freezing, drying and heat!

TFSN Reporter: So you are a spore-former?

Mr L. monocytogenes: You are too clever, but no!  I am one a few that have these resistant abilities without producing spores.  

TFSN Reporter: You are a very clever man, I mean bacterium, then? From farm to fork to mouth...with very little or no resistance and then?

Mr L. monocytogenes: My primary site of infection is through the intestine, the epithelium of the intestine to be exact, where I invade non-phagocytic cells via a unique “zipper mechanism” and then get taken up into the cell cytoplasm through a series of mechanisms, proliferate and start my wave of pathogenesis.

TFSN Reporter: So you take a roller-coaster ride through our gut and when you get into our cells you cause havoc?

Mr L. monocytogenes: Havoc is the understatement of the millennium...from the time I infect the person to the onset of symptoms can range from 12 hours to three weeks, and the number of troops needed for the invasion to be victorious is less than 1000 organisms.  If I cause meningitis, you only stand a 30% chance of survival, septicaemia a 50% chance. Should I infect perinatals or neonatals, their survival rate is less than 20%!

TFSN Reporter: OMG, you are indestructible!

Mr L. monocytogenes: Actually I am not.  Treatment with antibiotics penicillin and ampicillin are very successful, especially during pregnancy.  And individuals allergic to penicillin, can also be treated with sulfamethoxazole.

TFSN Reporter: Your honesty may be to your detriment, but thank you L.mono. Your life facts will surely be used to prevent you from causing any more outbreaks as food manufacturers and food consumers will hopefully use what you have told us to prevent your incidence in their food.

Mr L. monocytogenes: You are most welcome! I am able to tell you this as once I have infected you, your chance of survival is quite small should you not find me in time. Remember I am a living organism that also need to survive in the world and my aim in not to harm people or any other living creature.

TFSN Reporter: Prevention is thus better than cure. Well that is the end of our Listeria monocytogenes autobacteriography and part three of our Meeting with Microbes Series.

Brace yourself..... you are becoming macroscopic..... Honey, I shrunk the readers ends!

Remember small steps and you will...
Let’s rephrase are MAKING SENSE OUT OF MICRO....


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