Foodborne gastroenteritis caused by Listeria

Listeria monocytogenes - most important human pathogen causing the disease listeriosis ; is of great concern to special risk groups Susceptible groups - pregnant women and their fetuses, cancer patients and others undergoing immunosuppressive therapy, diabetics and cirrhotics and the elderly

Characters 1.Listeria monocytogenes - facultative intracellular pathogen – The organism enters the body through the intestine and has a variable incubation period from 1 day to a month or longer – Ingested cells enter the body through ileal villi cells, subsequently taken up by macrophage cells in the bloodstream, multiply inside the host cell and released after bursting of macrophages and liberated cells infect other cells 2.Listeria is widely distributed in the environment, human beings and a variety of animals including seagulls – Listeria sp. other than L. monocytogenes - common in tropical areas – Isolated from seafoods including refrigerated and frozen crabmeat, reports of listeriosis involving seafood is rare

3.Listeria - heat resistant but unable to survive in foods receiving adequate heat treatment – L. monocytogenes in cooked seafood - cross-contamination 4. Listeria - aerobic or facultatively anaerobic; grow well under reduced levels of oxygen in packaged products – Listeria can also survive and grow under refrigeration temperature and also survive freezing conditions 5. Contaminated food - vehicle of L. monocytogenes – Isolations from seafood, ability to grow in in chilled smoked salmon at +4 o C - possible involvement of sea foods in the transmission of Listeria monocytogenes.

Listeria species involved in food poisoning L. monocytogenes, L. ivanovii and L seeligeri - associated with disease in humans and / or animals Listeria - identified by serotyping Types 1-7 are known, with Types 1/a, 1/b, and 4b predominating as both environmental and clinical isolates The serotyping scheme is based on both somatic and flagellar antigens Phage typing has also been employed as a method of further identifying isolated strains L. monocytogenes is subdivided into 13 serovars on the basis of somatic (O) and flagellar (H) antigens.

Symptoms Listeria infections result in septicemia, meningitis and encephalitis, and enteritis Mortality rate of 29% is noticed among patients in a New England outbreak involving fluid milk Causes the transitory flu-like symptoms at the initial stage of infection with or without symptoms of stomach disturbances and diarrhea Listeriosis occurs only after the attainment of severe form of septicemia, encephalitis, lesions, or meningitis Mainly in individuals who are not immunocompetent

Prevention of outbreak To prevent risk due to L. monocytogenes, FDA in the US has recommended complete absence in ready-to-eat seafood products such as crabmeat or smoked fish This restriction does not apply to raw product that will be cooked before eating Low number of L. monocytogenes is allowed in other types of products in which the organism is shown to die-off Numbers greater than 10 L. monocytogenes / g are likely to constitute a risk to human beings particularly predisposed persons (very old, very young or immuno- suppressed) Following proper GMP and factory hygiene is expected to maintain the level of L. monocytogenes contamination on fish products at very low level of less than 1- 10/g.