Back To CourseMicrobiology 101: Intro to Microbiology
20 chapters | 207 lessons
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Angela has taught college Microbiology and has a doctoral degree in Microbiology.
It happens to everyone at one time or another. That Fourth of July barbeque is stretching into its fifth hour with a couple more to go before the fireworks. Your sixth volleyball game has just ended, so you decide to head back over to the buffet table and see what's left. The burgers are gone. So are all four different varieties of tortilla chips. And finally, at the end of the table, you see it: Aunt Jean's delicious, world-famous potato salad. At least, it was delicious five hours ago. You know you shouldn't eat it, but volleyball has left you ravenous. Surely a few scoops of this warm, mayonnaise-based side dish can't hurt you. It would certainly hit the spot. With only token hesitation, you grab a plastic spoon and dive in!
If you haven't already guessed, you never make it to the fireworks. Instead, you spend the next six hours in the bathroom vomiting. Inside that innocently tantalizing potato salad, a potentially deadly pathogen was growing, reproducing, dying and releasing toxic compounds. Add your name to the ever growing number of those stricken with a foodborne illness.
A foodborne illness is any illness that results from consuming food contaminated with pathogenic microorganisms, or toxic compounds released by microorganisms. The disease-causing microorganisms are most often bacteria, but can also include fungi, viruses and protozoa. Your food usually travels a long distance from its origin before it gets to your plate. It can be handled by many different people and exposed to many different conditions. This results in many potential points where food can become contaminated.
Some microbes responsible for foodborne illnesses are members of the normal microflora of the food organism. So, for example, the bacteria that are naturally found in the cow intestinal tract can end up contaminating the slabs of beef during butchering. This kind of contamination can occur during slaughter or during any point in the food's processing.
Vegetables and fruits are not immune to contamination with foodborne pathogens, despite the fact that they are picked, not slaughtered. Irrigation water or fertilizers sprayed on crops can be contaminated with animal or human waste containing foodborne pathogens.
Contamination that occurs early in the food production process has the potential to make many people sick over a wide geographic area after foods are distributed. A vehicle is a nonliving source of pathogens that infects large numbers of individuals. In 2012, five states in the northeastern United States had an outbreak of E. coli that caused illness in 33 people. In this case, the outbreak was traced to a contaminated batch of prepackaged leafy greens. The leafy greens were the vehicle that delivered the E. coli to the public, hitting several states due to the widely distributed food.
More often, foodborne illnesses are a result of a more local contamination. The person preparing or serving the food is the source of the microbes, usually by the fecal-oral route. Poor personal hygiene, insufficient cleaning of preparation surfaces and reusing utensils before and after cooking are common ways that food becomes contaminated with pathogenic bacteria.
Insufficient cooking time or temperature can allow any pathogens already present to survive, and failure to promptly refrigerate leftovers can allow these organisms to grow and reproduce. This mode of contamination usually results in foodborne illness that impacts only the limited few that consume the food around the same time and from the same infection source.
There are two general types of foodborne illness: food poisoning and food infection. Let's take a minute and look at each individually.
Food poisoning, also called food intoxication, is any illness caused by ingesting food containing preformed microbial toxins. The microbes don't need to be alive or actively growing at the time of consumption. They form the toxins and release them directly into the food. The toxins generally cause symptoms immediately, only taking around one to six hours to develop. The time to develop symptoms can vary depending on the kind of toxin and its concentration in the food.
Let's use the example of Clostridium botulinum, the causative agent behind botulism food poisoning. C. botulinum will only grow in protein-rich environments with no oxygen. When C. botulinum is actively growing, it releases a toxin into its environment.
If that jar of green beans that your grandmother canned for you last fall was contaminated with C. botulinum, it is probably now full of both green beans and botulism toxin. Opening the jar introduces oxygen, which stops C. botulinum from growing, but does not impact the toxins already in the jar. If you eat the beans without cooking them, you are eating botulism toxin, which can cause a potentially fatal paralysis. You also ate the Clostridium bacteria, but they are unable to continue growing, making them harmless to you. The paralysis is a result of the toxin alone, not the C. botulinum cells. It is important to note, cooking the food before eating it will inactive the toxins, making those green beans safe to eat.
Food infection is any illness caused by an active microbial infection resulting from ingestion of a pathogen-containing food. In this case, symptoms are a result of the growth of viable microbes inside your body, combined with any toxins produced by those microbes. Since the microbes are actively growing, it can take longer for symptoms to develop. It can take anywhere from six hours to three weeks before the microbial populations are large enough to cause disease.
Let's look at one common bacterial food infection culprit, Salmonella. Let's say the cook in your favorite restaurant uses the same knife to slice your grilled chicken sandwich that he used to fillet the raw chicken breast. The Salmonella on the knife ended up on your entrée, and then eventually in your mouth. After ingestion, these bacteria adhere to the intestinal walls and begin growing and dividing. This causes irritation, inflammation and tissue destruction.
There is a lag time before the symptoms develop, as the population of Salmonella grows large enough for the total inflammation to begin causing symptoms. Some Salmonella cells die, releasing a toxin that causes further inflammation of the gastrointestinal tract. Both of these situations lead to fever, nausea, cramping and diarrhea. In this case, the combination of the live bacteria and the toxin released by the dying bacteria are responsible for your symptoms.
A foodborne illness is any illness that results from consuming food contaminated with pathogenic microorganisms, or toxic compounds released by microorganisms. This can include bacteria, fungi, viruses and protozoa. A vehicle is a nonliving source of pathogens that infects large numbers of individuals. Commercially produced and distributed food products often serve as vehicles for foodborne illness, capable of causing disease in many people over a wide geographic area.
Foodborne illnesses can be broken down into two general types. Food poisoning, also called food intoxication, is any illness caused by ingesting food containing preformed microbial toxins. In this case, the causative microbe does not need to be alive to cause disease. The presence of the toxin is enough for symptoms to develop. Food infection is any illness caused by an active microbial infection resulting from ingestion of a pathogen-containing food. Symptoms are caused by a combination of tissue damage from the actively growing microbes and impacts from toxins released during the microbe's life and after death.
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Back To CourseMicrobiology 101: Intro to Microbiology
20 chapters | 207 lessons