ABSTRACT
Listeria have been observed to infect different groups of animals, ranging from birds like chicken, quail, partridge and ostrich, to small ruminants like sheep and goat, to larger cattle like cows and buffaloes. The pathogen has been identified in the meat and milk of animals, and in fish and fishery products. The causative agent Listeria monocytogenes, a Gram-positive bacillus, has been observed to live freely in the environment. The bacterium multiplies intracellularly and passes from one cell to neighbouring cells without lysis of the first cell. Several virulence determinants have been reported to play a role in host-pathogen interaction and propagation of the pathogen. These factors are of interest to scientists developing diagnostic techniques. The bacterium is observed to transgress across the intestinal, foeto-placental and blood-brain barriers, leading to its systemic spread all over the body of the host. This spread explains the observed characteristic, viz., gastroenteritis, septicaemia, encephalitis, meningitis, meningoencephalitis and rhombencephalitis in infected animals. New techniques for diagnosis with improved specificity and sensitivity for efficient detection as alternatives to classical culture-based techniques have been developed. These include methods based on antigen-antibody interactions such as ELISA and lateral-flow immunoassay. More recently, highly specific and sensitive nucleic acid-based detection methods such as DNA molecular typing, pulse field gel electrophoresis (PFGE), restriction fragment length polymorphism (RFLP) and ribotyping, quantitative real-time PCR, multiplex PCR, nucleic acid sequence-based amplification (NASBA), loop-mediated isothermal amplification (LAMP), oligonucleotide microarrays and biosensors with labeled DNA probes have been developed. The present chapter reviews all these methods and future perspectives in diagnosing the disease.
