Back to basics...

Meeting with the microbes

Part 1

Over the last five articles you have journeyed through the microbiology laboratory, conversed with the competent laboratory manager, who was able to assist you in selecting what tests to perform on your food samples. And once you received and correctly interpreted your laboratory report, you were able to understand and correct any non-conformances that arose from test results that were out of specification. All these small steps have taken you that much closer to making sense out of the invisible world of microbiology, well done!

But in order for you to continue keeping the bacteria and other microorganisms under control in your factory and product, you need to meet with them face to face. You need to join them in their world, become a microbe for a day. Over the next few issues of this series we will be taking you to microscopic world of all the major bacterial players in the food industry, including Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, Salmonella spp. Clostridium and Vibrio spp. to name a few. Each article will be an exclusive “autobacteriography” of the organism.

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


PART 1: Staphylococcus (S.) aureus

The Food Safety Network (TFSN) Reporter: Good day Mr. Aureus and welcome to this live and exclusive interview with The Food Safety Network. We are privileged to have to you on our website.


Mr. S. aureus: Thank you for having me. Hopefully this interview will ensure me and my fellow bacteria are no longer seen on a microscopic level.

TFSN Reporter: Well that will definitely not be the case during this interview as I am all on your microscopic level, as well as the readers....all shrunken for today! Let’s begin. Please tell us how who got your name, what it its significance and does it have something to do with your golden tan?


Mr. S. aureus: Ha ha, you are observant! Yes, my first name or genus, Staphylococcus, stems from my spherical shape (coccus) and this is one of the three shapes that bacteria are classified according to. The other shapes include rod (Bacillus) and curved/spiral, after my fellow bacterium Bacillus cereus and Vibrio cholera respectively. When I am cultured on standard growth media or agar, each colony forming unit that I form is golden yellow in colour, which is “aureus” in latin. Thus my last or species name is aureus. Upon microscopic examination I appear in pairs, short chains or grapelike clusters and stain gram positive.


TFSN Reporter: Fascinating! Are all bacteria named according to such characteristics?


Mr. S. aureus: Yes, most of us are named after a growth characteristic and/or after the person that discovered us. For example, Escherichia coli (E.coli) was proudly named after Professor Theodor Escherich, the German pediatrician and bacteriologist, in 1885. I was discovered in 1880 in Scotland by a surgeon Sir Alexander Ogston when he isolated me from pus from an abscess that he encountered during surgery.


TFSN Reporter: That is amazing and quite disgusting – with due respect to you! Let’s get down to the nitty gritty...why is food so threatened by your species?


Mr. S. aureus: Yes I am aware that humans refer to us as pathogens or disease causing bacteria. This is true... as some strains of my species are able to cause food poisoning. We are capable of producing a highly-heat stable protein toxin (enterotoxin) that causes illness in your species (humans). Our ability to cause illnesses can range from minor skin infections, such as pimple or boils to life-threatening diseases such as pneumonia, meningitis, Toxic Shock Syndrome (TSS) and sepsis.


TFSN Reporter: Explain how you cause disease, specifically food poisoning.


Mr. S. aureus: I mostly inhabit the skin and nose of humans and other animals. Less commonly I can also be found in the throat. However, under these circumstances, I don’t generally cause an infection and thus the host I inhabit is not treated. I am also able to survive for hours and even months on dry environmental surfaces. Once I infect other tissues, like skin or mucus linings, I can cause boils. I can then be spread to and contaminate foods, by this pus or infected mucosal linings, through improper handling of the foods by infected food handlers.


TFSN Reporter: Okay, I am now nauseous...explain what foods may be incriminated.


Mr. S. aureus: Frequently, I contaminate and love meat and meat products; poultry and egg products; egg, tuna, chicken, potato and macaroni salads; cream-filled bakery products like pastries, éclairs and pies; sandwich fillings and dairy products. Any food that requires considerable handling, especially human handling, during preparation and that are kept at slightly elevated temperatures after preparation, provides me with a perfect environment to grow.


 TFSN Reporter: So you are saying that food handlers that have boils, for example, are able to contaminate the above foods as a result of poor hygiene practices?


 Mr. S. aureus: Precisely! I love food handlers! Food handlers are my main vehicle of transportation to food resulting in food contamination and food poisoning outbreaks. Equipment and environmental surfaces also contribute to my existence, but are less frequently implicated.


 TFSN Reporter: So you cause food poisoning outbreaks amongst humans when we eat food that you have “contaminated” – again with due respect?


 Mr. S. aureus: Yes and no! Humans are intoxicated when they ingest the enterotoxins I produce in the foods. But I can only produce such enterotoxins, if the temperature in which I am growing is ideal. So if you do not keep the food hot (60°C or above) or cold (7.2°C or below) enough, I will grow and produce toxins that can make you ill. What I am saying is that you can control my growth, so I am not entirely to blame for my ability to cause disease in your species!


 TFSN Reporter: So in a court of law you would only plead guilty under extenuating circumstances?


 Mr. S. aureus: You amuse me...but yes! I can only get to your food by improper and unhygienic handling of the food and furthermore will only survive and possibly produce toxins if you do not adhere to good manufacturing practices during food preparation.


 TFSN Reporter: Explain this enterotoxin phenomenon.


 Mr. S. aureus: Under ideal growth conditions, I must be able to grow and multiply to numbers of >100 000 cfu/g before I can produce any toxins. And only a toxin dose of less than 1mg in the in the food can produce symptoms of such intoxication. So I need to be present in very high numbers in the food as well as produce a minimum amount of the toxin before I can cause any symptoms. I do believe that all people are susceptible to these toxins, however, symptoms may vary.


 TFSN Reporter: What is the nature and symptoms of this disease? Should we be very scared of you?


 Mr. S. aureus: Of course! Just kidding! If you have allowed me to enter your food chain and have not kept your part in preventing me from surviving, then you should allow me to do what I best at, live! Once you have consumed me and my toxins, onset of symptoms are rapid and in many cases acute. However, symptoms depend the person’s susceptibility to the toxin, amount of contaminated food eaten, amount of toxin in the food ingested and the immune system of the person. If all above criteria are met, common systems include nausea, vomiting and abdominal cramping. In severe cases, symptoms also include headaches, muscle cramps, changes in blood pressure and pulse rates.


 TFSN Reporter: How long do such symptoms last?


 Mr. S. aureus: Usually I only make you ill for about two days. However, sometimes a full recovery can take up to three days or in severe cases some times longer. Death from this food poisoning is very rare, but may occur in infants, elderly or severely debilitated individuals.


 TFSN Reporter: So in most cases the infected person will recover? Can you give us an example of outbreaks that you have been responsible for and their severity?


 Mr. S. aureus: In Texas, 1364 children became ill after 5824 children ate lunch at 16 elementary schools. Lunches prepared in a central kitchen and transported to the schools by trucked were implicated in the outbreak. 95% of the children had eaten a chicken salad that was prepared the afternoon before lunch was served. Frozen chickens were boiled for 3 hours and after cooking and deboning, were cooled to room temperature with a fan. The chicken was then ground into small pieces and placed in 12 inch deep aluminium containers and stored overnight in walking refrigerator at 5-7°C. The next morning, the salad was made and the mixture blended with an electric mixer. The salads were placed in thermal container and transported to the school between 9h30 and 10h30. Here it was kept at room temperature until it was served at 11h30. After extensive microbiological testing of the salads, my family was found at very high numbers.


 TFSN Reporter: I can see from this incident, that as a results of the humans not following correct procedures, you were able to contaminate the food and make many children sick.


 Mr. S. aureus: Yes indeed! As the Food Safety specialists, can you tell me why I was able to grow so well?


 TFSN Reporter: Thank you for your confidence in us. Yes, contamination most probably occurred during deboning. Cooling was not rapid enough (storage in 12 inch-deep containers) and you were able to multiply during storage in the warm classrooms after the food was delivered to the schools. Do you think the food preparers contaminated the food?


 Mr. S. aureus: Oh yes! This incident could have been prevented it the food handlers were screened before handling of the chicken occurred. They may even have been carriers of Staphylococcus. Furthermore, my growth could have been prevented through rapid cooling of the cooked chicken and storage of the finished salads in a refrigerator from the time of preparation to consumption by the scholars.


 TFSN Reporter: Thank you so much for being so honest with us during this interview Mr. Aureus. Your life facts will surely be used to prevent you from causing any more outbreaks as food manufacturers will use what you have told us to prevent your incidence in their food products.


 Mr. S. aureus: No, thank you! 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. Where I am found naturally, does not cause harm to anyone, it is only when hygiene practices or good manufacturing practices are not adhered to and I am transferred to other habitats that I become potentially pathogenic.


 TFSN Reporter: Well that is the end of our Staphylococcus aureus autobacteriography and Part One 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 that... you are MAKING SENSE OUT OF MICRO....


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