Listeria monocytogenes, a little too close to home!

Emily Zelger (11 AM Micro) saw the Salmonella  outbreak from frozen dinners very alarming, and submitted this guest posting about another food-borne outbreak–this one right next door in Maryland. Listeria infections are actually pretty common, however as Emily notes in her summary below, the biggest concern is with pregnant women, as Listeria infections can lead to spontaneous miscarriage due to the ability of the organism to cross the placenta. It is essential that health care workers then be cognizant of the risks due to Listeria as part of pre-partum health care, and to warn expectant mothers to avoid infection.  Here is Emily’s summary:

6a00d8341c5e1453ef01348647b483970c-800wiSeven people of Hispanic descent in the state of Maryland have been diagnosed with listeriosis, an infection caused by the Listeria monocytogenes bacteria. One person in California was also infected, but has since died from the infection. The outbreak had occurred from August to November of 2013.

The Maryland patients reported that they had all eaten a Hispanic-style soft cheese manufactured by Roos Foods in Delaware. In each of these cases, the patients bought the cheese from the same grocery store chain. A laboratory in Virginia collected samples of the cheese and confirmed the presence of Listeria monocytogenes in it. All consumers were warned by the Maryland Department of Health and Mental Hygiene not to eat any Roos Foods cheese products, in order to prevent a possible further spread of the outbreak.

Listeriosis is typically caused by eating contaminated food, such as the soft cheese mentioned above. Symptoms of listeriosis can include head ache, stiff neck, confusion, loss of balance, fever, muscle aches, and convulsions. If an infection is caused in a pregnant woman, it can lead to miscarriage, still birth, premature delivery or a serious infection to the newborn child. Five of the cases in Maryland were related to a pregnancy. Three of these include newborn children and the other two cases related to pregnancy were mothers of two of the children that had contracted the infection. Typically, infants, the elderly, and people with a weak immune system pose the greatest risk for developing listeriosis.


Case count map of listeriosis, as of Feb. 21, 2014

Case count map of listeriosis, as of Feb. 21, 2014; 80% of the cases have been in Maryland

Listeriosis can be diagnosed by isolation from blood, spinal fluid, or amniotic fluid in a clinical laboratory on a selective media plate to determine the presence of L. monocytogenes in the body. If the diagnosis is confirmed, listeriosis can be treated with antibiotics such as ampicillin.

Listeria monocytogenes is a low G and C, Gram positive, bacillus shaped bacteria that is also a facultative anaerobe. It can survive in an environment with or without the presence of oxygen. L. monocytogenes can reproduce inside human body cells and destroy red blood cells. L. monocytogenes moves by way of peritrichous flagella at room temperature, but at human body temperature, the bacterium does not make any flagella. Because it doesn’t make any flagella at body temperature, the bacterium can move within host cells by way of actin rockets, produced by the polymerization of actin filaments. L. monocytogenes has thirteen serotypes that are capable of causing disease in humans, but 90% of diseases come from just three of the thirteen serotypes. The infection this bacterium causes is responsible for the most deaths among food related bacterial pathogens. Recent outbreaks of listeriosis due to Listeria monocytogenes have come from foods such as cabbage, cheese, and cantaloupes. These outbreaks often come from a single manufacturer.

It is possible to take a few precautions to prevent contracting listeriosis. All food should be washed and handled carefully, cooked thoroughly, and stored properly to ensure its safety. Choosing safer foods (pasteurized milk as opposed to raw milk or avoiding soft cheeses, for example) can also help prevent a listeriosis infection.



About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on February 24, 2014, in Guest Post, Wash your hands!. Bookmark the permalink. Comments Off on Listeria monocytogenes, a little too close to home!.

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