An elderly man finds himself struck with a high fever, severe muscle aches, and the runs. What could possibly be the cause of these symptoms? The only thing that he had done that day was eat out at a local burger restaurant. Did he get food poisoning? Well these symptoms are definitely a sign of food poisoning and more specifically the serious infection, listeriosis, caused by the bacteria Listeria monocytogenes.
L. monocytogenes has many fascinating properties. It is a non spore-forming, Gram-positive, rod-shaped bacterium. It is a microaerophilic, facultative anaerobe and intercellular pathogen.(2) It is capable of growing at temperatures as low as 3°C, which makes it very easy to replicate despite refrigeration.(3). Its uses flagella as a means of motility outside a host cell.(4)
With all these unique characteristics, L. monocytogenes begins its plight of attachment and invasion of the host. The bacterium is thought to attach to intestinal cells by means of D-galactose residues on its surface, which are capable of adhering to D-galactose receptors. Once attached the L. monocytogenes is taken into the cell by induced phagocytosis and eventually produces listeriolysin (LLO) as a means of escape from the phagosome. It then multiplies rapidly in the cytoplasm and polymerizes actin filaments to allow it to move within the cytoplasm and begin invading adjacent cells.(4)
Before L. monocytogenes can begin this process it must first be contracted. The microbe is mostly found in soil and water; therefore, vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can also pick up the bacterium and contaminate meats and dairy products. Other than being found in raw meats and vegetables, L. monocytogenes can be picked up by foods such as soft cheeses and deli meats after processing. The bacterium can be killed via pasteurization and cooking.(1) Therefore, it is essential to take precaution when making and purchasing food to avoid picking up this bacterium.
Once the host has contracted L. monocytogenes the symptoms of listeriosis begin to take effect. As mentioned above, fever, muscle aches, and gastrointestinal symptoms such as nausea or diarrhea are the first signs. Symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions are a sign that the infection has spread to the nervous system.(1)
L. monocytogenes usually only causes symptoms in certain types of people. The average person that contracts the bacterium will not show the symptoms of listeriosis. Pregnant women are said to be 20 times more likely to develop listeriosis than a healthy person and total to one-third of the cases of listeriosis. Often the newborn child of an infected mother can develop the symptoms. Others that often show symptoms include persons with weakened immune systems due to such things as cancer, diabetes, kidney disease, and AIDS. The elderly are also very susceptible to listeriosis. If diagnosed early, treatments are available to treat the symptoms before it becomes deadly.1 There are approximately 1600 cases of listeriosis and 415 deaths annually in the U.S.(3) Therefore, if you are pregnant or have a weakened immune system extra precaution should be taken.
Despite the terrible things that L. monocytogenes can cause it could possibly be used in the future as a vaccine for breast cancer. Research by University of Pennsylvania School of Medicine has been able to use cancer vaccines based on L. monocytogenes to cure mice of breast tumors. This could eventually be used in humans as a cure for cancer.(5) Although it can give you a case of the runs, its possibility as a cure for cancer makes L. monocytogenes a bacterium we don’t want to completely exterminate.
References
2. http://biology.kenyon.edu/Microbial_Biorealm/bacteria/gram-positive/listeria/listeria.htm
3. http://vm.cfsan.fda.gov/~mow/chap6.html
4. http://textbookofbacteriology.net/Listeria.html
5. http://www.uphs.upenn.edu/news/News_Releases/sep05/Listeriavacc.htm
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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