Listeirosis: Listeria Bacteria and Food Poisoning

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Recent Lysteria Outbreak from Contaminated Cantaloupes - Scott Bauer, USDA

Listeria monocytogenes is a species of hardy Gram-positive bacteria that can cause deadly food poisoning.

Listeria Outbreak from Contaminated Cantaloupe

This pathogenic bacterium has recently made headlines with an outbreak linked to tainted cantaloupe, which, as of the end of September 2011, has resulted in nearly 100 cases of food poisoning and a greater than 10% death toll, the most severe Listeria outbreak since 1985.
This outbreak is expected to generate more cases, as Listeria is a slow growing bacterium, and infection can take months to manifest. This is the first time that Listeria had been known to contaminate whole cantaloupe, and the FDA is currently working hard to determine how the contamination occurred.

How Listeria Infects Its Host

Listeria is a talented microbe with several features that make it an especially dangerous pathogen. It is considered a psychrophile; a microbe that can thrive at cold temperatures. While refrigeration slows the growth of most microbes, chilly temperatures do not inhibit Listeria.
Listeria is also an intracellular pathogen that tricks host body cells into engulfing the bacteria. Once inside a host’s cell, the bacterium can grow, thrive and stay hidden from the immune systems, as it spreads directly from cell to cell.

Who Is At Risk from Listeria Infection?

Listeria is rarely dangerous to healthy adults, who, if infected, may show no symptoms, or develop a mild flu-like illness. However, listeriosis, the disease caused by Listeria monocytogenes, can be deadly in vulnerable populations, such as pregnant women, fetuses, infants, the elderly, and those with compromised immune systems. In these populations, the bacteria can travel through the blood to cause deadly meningitis, which kills up to 30% of vulnerable patients infected.

How to Protect Yourself and Your Family from Listeriosis

Although Listeria is most often found in animal products, and can be destroyed by cooking, the recent outbreak in fruit is a reminder that any food can be contaminated, particularly undercooked vegetables, lunch meats, unpasteurized milk, and cheeses.
For those populations at high risk, thoroughly cooking vegetables and meat, and avoiding high-risk raw products, can reduce the risk of infection. Although washing produce is no guarantee that dangerous microbes will be eliminated, it is always a good idea, as washing can reduce microbial populations on the surface of fruits and vegetables.
Antibiotics can be used to treat listeriosis, although the pathogen is resistant to some classes of antimicrobials.
For more information on microbiology and science in general, see the science education website Science Prof Online.

Sources

Bauman, R. (2012) Microbiology: With Diseases by Body System. Benjamin Cummings.
Booth, M. (2011) “Canteloupe-linked listeria's toll expected to keep rising.” Denver Post