Listeria monocytogenes, Haemophilus influenzae, and Mycobacterium ulcerans

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  • Topic: Haemophilus influenzae, Meningitis, Hib vaccine
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Research Topic: Listeria monocytogenes, Haemophilus influenzae, and Mycobacterium ulcerans Part 1: Listeria monocytogenes
Listeria monocytogenes is a bacterium that is originated in food and can cause the serious illness of Listeriosis. Listeriosis is a serious disease for humans; the overt form of the disease has a mortality rate greater than 25 percent1. This is a Gram-positive bacterium, and is mobile by means of flagella. Listeria monocytogenes can be found in nature in soil, water and animal feces, meaning it can be also be tracked to animals. In addition to humans, at least 42 species of wild and domestic mammals and 17 types of birds can harbor listeria monocytogenes as well as crustaceans, fish, oysters, ticks, and flies. It is also reportedly carried in the intestinal tract of 5-10% of the human population without any apparent symptoms of disease1. Listeria monocytogenes is able to resist the deleterious effects of freezing, drying, and heat remarkably well for a bacterium that does not form spores2. A human can consume this bacterium by eating a raw vegetable that grew in infected soil, or by eating improperly processed deli meats and unpasteurized milk products3. Healthy people rarely become ill from listeria monocytogenes infection. Possible complications due to the bacteria are blood infections and inflammation of the membranes and fluid surrounding the brain (meningitis). Other side effects that may develop are typical cold or flu-like symptoms. The real risk of infection is in the elderly, new born children, and pregnant women. During pregnancy, a listeria monocytogenes infection is likely to cause only mild signs and symptoms in the mother. The consequences for the baby, however, may be devastating. The baby may die unexpectedly before birth or experience a life-threatening infection within the first few days after birth3.

The dangerous factor about the listeria monocytogenes is that the bacterium is able to grow in fresh food. The organisms can grow at 4o C which means that organism replication continues in refrigerated foods4. Therefore it is impossible for someone to know if he/she is purchasing food that 100% does not contain this bacterium. The current method the FDA uses to analyze food for possible contamination is complex and time consuming. The method requires 24 and 48 hours of enrichment, followed by a variety of other tests. Total time to identification is from 5 to 7 days, but the announcement of specific non-radiolabeled DNA probes should soon allow a simpler and faster confirmation of suspect isolates. With new DNA technology may even permit 2-3 day positive analysis in the future. Currently, FDA is collaborating in adapting its methodology to quantitate very low numbers of the organisms in foods2. This should drastically help prevent diseases that are caused through food consumption.

Cases of Listeriosis in humans were not reported till about 1960, as the infection was only previous seen in animals. In 1981, there was an outbreak that involved over 100 people in Canada. Thirty-four of the infections occurred in pregnant women, among whom there were 9 stillbirths, 23 infants born infected, and only two live healthy births. Among 77 non-pregnant adults who developed overt disease, there was nearly 30% mortality. The source of the outbreak was coleslaw produced by a local manufacturer1. Even with increasing awareness of the bacteria and ways to prevent it from getting into food through processes developed by the FDA, there have still been recent outbreaks. As of October 26, 2012, there have been twenty people reportedly hospitalized due to the listeria monocytogenes bacterium in 13 different states and the District of Columbia. Nine of the illnesses were related to a pregnancy; three of these illnesses were diagnosed in newborns. The other 13 ill persons range in age from 30 years to 87 years, with a median age of 77 years. Four deaths have been reported, one each from Minnesota, New...
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