Performance of the Municipal Wastewater Treatment Plant for Removal of Listeria monocytogenes
Listeriosis is essentially a foodborne disease caused by L. monocytogenes and to some extent L. ivanovii. The disease condition vary from that affect immunocompromised patients to febrile gastroenteritis and prenatal infections associated with fetal loss or abortion in humans and animals.  Although rare, the disease reported to have very high mortality rare (20-50%), thus making it of serious public health concern.
L. monocytogenes commonly is a saprophytic organism living naturally in the plant-soil environment. The ubiquitous nature of L. monocytogenes results in contamination of numerous food products including meat, milk and dairy products, sea foods and vegetables. A possible agricultural
route of human exposure to Listeria is through the ingestion of uncooked food crops grown in the lands irrigated with contaminated water and/or fertilized with Listeria-contaminated biosolids.
L. monocytogenes has been detected in wastewater,[5-12] sewage sludge[5,7,13-15] and L. innocua has been detected in compost and irrigation water. Sewage sludge can be regarded as a reservoir of L. monocytogenes and the presence of this pathogenic bacterium in such fertilizer would increase the risk of crops contamination. Therefore, biological monitoring of the presence of pathogenic bacteria in the effl uent and sludge of sewage treatment plants is of special importance. In addition, numerous rules and regulations ratifi ed for the existence of certain microorganism in effl uent and sludge. For instance, US Environmental Protection Agency (EPA) has been setup an extensive regulation for reuse of effl uent and sludge in agriculture lands. However, recent studies have been indicated that the traditional standards are not effective on environmental dissemination of new emerging microorganisms. In the other hand with reports of inadequate removal of Listeria from wastewater in developed world,[19,20] one can safely presume that wastewater treatment plants in Iran are insuffi cient at removing these pathogens from wastewater infl uents prior to reused for irrigating the farmlands.