Listeria and it's effects

                                                                 INTRODUCTION
Listeria  is a group of gram positive bacteria with a low G+C content in their DNA. They are aerobic or facultative anaerobes with short rods and are catalase positive and move by peritrichous flagella.
They are medically important in Microbiology because of their effects as food spoilage organisms.
                                                                     TAXONOMY
Kingdom: Bacteria
Phylum:    Firmicutes
Class:          Bacilli
Order:        Bacillales
Family:      Listeriaceae
Genus:       Listeria
Specie:      monocytogens
(Note that there are other Listerial species but our focus  is on Listeria monocytogens since it is the main food spoilag organism.
DISTRIBUTION
Listeria is widely distributed kin nature and can be isolated from the soil, vegetation, humans and many other animal reservoirs like sheep ,goat, guinea pig, horses, rodents, birds and crusteceans.
PATHOGENESIS
Listeriosis is the disease caused by a specie of Listeria called Listeria monocytogens. This organism is a human pathogen but can also affect other animals. It is a food borne pathogen having varying incubation periods and can grow at a minimum temperature between 0 - 7 degrees celsius, optimum between 20 - 30 degrees celsius and a maximum temperature around 35 degrees celsius making it easily adaptible to various enviromental conditions.
  It affects immunocompromised individuals, the aged, pregnant women and infants. Source of contaminated foods like unpasteurized milk, soft cheese, vegetables and meat. It causes invasive syndromes affecting the cell mediated immunity and is manifested by stil lbirth, septisemia and meningitis.
IDENTIFICATION/CULTURING
Listeria monocytogens can be identified by radioactive probes on food. For example radioactively labelled Listeria monocytogens probe against 100 Listeria cultures and only L. monocytogens show sequence homology and bind the DNA probe while other species do not bind the probe because of different sequences in genes.
TREATMENT
Listeriosis is treated by intravenous administration of antibiotics like Ampicillin or Penicillin G.
Also Teicoplanin a Glycopeptide antibiotic from the Actinomycete Actinoplanes teicomyceticus which is similar in structure and mechanism to vancomycin is active against Listeria and other gram positive bacterial pathogens with fewer side effects.