Outbreak: listeria monocytogenes in cantaloupes

Valerie Weinborn

Outbreak: Listeria monocytogenes in Cantaloupes

I. News Citations

* New York Times: Listeria Outbreak Traced to Cantaloupe Packing Shed by William Neuman (October 19, 2011).
* Food Safety News: Listeria Outbreak: Cantaloupe Contamination By Mary Rodhschild (September 30, 2011).
* ABC News: CDC: Cantaloupe Listeria Outbreak Deadliest in a Decade by ChristinaCaron (September 28, 2011).
A total of 146 persons infected with Listeria monocytogenes were reported to CDC from 28 states, in the USA. Thirty deaths were reported. Among persons who died, ages ranged from 48 to 96 years, with a median age of 82.5 years. In addition, one woman pregnant at the time of illness had a miscarriage (CDC, 2011).

II. Organism Involved: Listeria monocytogenes1. Taxonomic Classification
The genus Listeria consists of seven species, which are L. monocytogenes, L. innocua, L. ivanovii, L. seeligeri, L. grayi, L. murralli, L. welshimeri. Within these seven species, although three of them can cause infection to animals or humans (L. monocytogenes, L. ivanovii, L. seeligeri) only Listeria monocytogenes is of importance as a pathogen of foodborneillness. It is a short bacillus (0.5 mm in diameter by 1 to 2 microns in length), gram-positive non-spore-forming, microaerophile. It presents motility, which is characteristically tumbling to grow at temperatures from 20 to 25 ° C (Pitt et al., 1999).
2. Growth Parameters
It can grow in the laboratory at a temperature range that goes between 1°C and 45°C, growing optimally between 3°C and 35°Cmay improve if kept under reduced oxygen conditions. Biochemically, all Listeria produce catalase, ferment glucose to acid without gas, and hydrolyzed esculin. Listeria monocytogenes typical fermented rhamnose but not xylose, and are weakly beta-hemolytic (Marth and Steele, 1998).
As a particular feature, it presents an unusual resistance to extreme environments (resisting temperatures between-0.4°C and 50°C) (Rubio et al., 1998), and even temperatures down to -20 ° C for two years and it is still viable after freezing and thawing repeatedly (Blood and Radostits, 1992). It can grow at pH 4.3 to 10.0, also in presence of sodium chloride 10%, and survive in chilled brine solutions of sodium chloride to 25.5% for 4 months. It also has the ability to resist pasteurization (Marth andSteele, 1998).
3. Ecology
Different researchers have isolated Listeria monocytogenes soil, sewage, fertilizers, dust, water and silos. The organism can be transferred from the intestinal tract animals to the human intestinal tract without causing disease (FDA, 2001); in fact it has been found in many domestic and wild animals, including birds and fish. Microorganisms can last up to three monthsin the feces of sheep, and been found to survive 11 months in moist soil, up to 16 in the feces of cattle, 207 days on dry straw over two years in dry soil and feces (Blood and Radostits, 1992).
4. Listeriosis
Listeriosis primarily affects immunocompromised adults, pregnant women, pregnancy babies, newborns, farmers, and veterinarians (Acheson, 2000). In adults, the disease manifests asbacteremia and encephalitis, predominantly in those who experience depression of cell-mediated immunity, ie, the highest incidence occurs in older people, where you have AIDS, cancer, diabetes cirrhosis and in those receiving immunosuppressive medications or have undergone transplantation (Hof et al., 1997).
Meanwhile, pregnant women also show susceptibility to S. aureus bacteremia, the diseaseusually occurs during the third trimester, enrolled as a simple flu-like illness. The fatal outcome is rare in the mother but in the absence of appropriate therapy, occur amnionitis and fetal infection; it comes to cause abortions or premature deliveries of infants with infantiseptica granulomatosis. Clearly, the latter clinical entity is associated with infections acquired in utero, although other...