Listeria Is Not Named After Its Discoverer Biology Essay
Listeria Monocytogenes can be farther characterized based on the presence of specific heat stable bodily ( 0 ) and heat-labile scourge ( H ) antigens. Based on the “ O ” and H ” antigens, strains of Listeria Monocytogenes, isolated from pathological beginnings are subdivided into serotypes: 1/2a,1/2 B, 1/2c, 3a,3b,3c,4a,4ab,4b,4c,4d,4e,4f,5 and 6. Serotypes 1/2a, 1/2b and 4b are responsible for greater than 95 % of all human infections ( French republics Pouch Downee, Keith Ito, 2001 ) .
Factors impacting growing and endurance of Listeria Monocytogenes.Listeria Monocytogenes is a psychotropic bacteria that is it has the ability to defy the cold temperature of infrigidation. However, Listeria Monocytogenes is besides thermo tolerant when subjected to temperatures above the optimum.The wide pH scope for growing for Listeria Monocytogenes allows it to last.
pH 7.0 – 7.5 is the optimal pH for the growing of Listeria Monocytogenes ( Dean, 1990 ) .The bacteriums can defy a high concentration of salt that is an environment with a low H2O potency.
It has been shown that the being can digest environments of 25.6 % Nacl for at least 132 yearss at 22A°C and 5 yearss at 37A°C ( Adams ; 2001 ; Lovette, 1989 ) .Furthermore the presence of other micro-organisms in the same medium ( on the same contaminated nutrient ) can do a lessening in the population of Listeria Monoctyogenes.Listeriosis:Besides known as the Circling Disease or Silage illness, Listeriosis is a sporadic bacterial infection caused by Listeria Monocytogenes.
It is a world-wide disease and a serious nutrient borne disease for worlds. The term Listeriosis encompasses a broad assortment of disease symptoms that are similar on animate beings and worlds.Persons of advanced age, pregnant adult females, new born and grownups with septic immune systems are usually prone to pull this disease. A normal individual without those standards mentioned above can besides be affected. He can be infected by devouring contaminated nutrient. Babies may acquire infected at birth itself if their female parent had consumed contaminated nutrient during gestation.
Harmonizing to the universe wellness organisation ( WHO ) , eruptions of Listeriosis have been reported from many states, including Australia, S Switzerland, France and the United provinces. Two recent eruptions of Listeria Monocytogenes in France in 2000 and in the USA in 199 caused by contaminated porc lingua and hot Canis familiariss.Health hazard of listeria:Hayes ( 1992 ) considered Listeria Monocytogenes as a low class pathogen since there is no clinical manifestation in healthy persons upon consumption of low Numberss of feasible cells.
Harmonizing to the centre for nutrient security and public wellness 1-10 % of the population is thought to transport Listeria Monocytogenes asymptomatically in the bowels ( May, 2005 ) .Vomiting, Nausea, Cramps, Diarrhea, terrible concern, irregularity ad persistent fever are the symptoms that may happen all of a sudden. Meningitis phrenitis is the infection of the encephalon and its environing tissue. Septicemia is the toxic condition of blood caused by listeria.
The overall mortality rate in the group of susceptible people reference in sectionaˆ¦ . Are 20 -30 % .Listeria Monocytogenes can be identified in tissues utilizing ELISA, PCR and other molecular techniques.
It is treated with antibiotics depending on the signifier of the disease.Mode of invasion and spread of Listeria in host cells:Listeria Monocytogenes is acquires by consumption. The bacteria must happen and adhere to the enteric mucous membrane or the enteric crypt cells, which are the merely uniform mucosal cells. Once the bacteria is phagocytosed, it becomes enclosed in a phagolysosome, a bomber cellular cell organ. Normally the low pH and the contents of the phagosomes are toxic to micro-organism, nevertheless, environment of low pH causes Listeria Monocytogenes to bring forth haemolysin, Listeriolysin O ( LLO ) .LLO lyses the cell membrane of the phagolysosome and this causes release of the Listeria into the cytol. Harmonizing to F.S Southwick and D.
L Purich all infective strains of Listeria produce Listeriolysin-O which is of import for their flight and pathogenesis.Once in the cytol, the bacteriums multiply and proliferate and the bacteriums become surrounded by an electron-dense stuff. The bacteriums are so known to be polarized at one terminal. The electron-dense stuff give the bacteria an extended bulges signifier and filopods which are in bends ingested by next cells and the rhythm begins afresh.Spreading from cell to cell without straight being in contact with the extracellular environment is how Listeria Monocytogenes invade the cells of its hosts.Isolation of Listeria Monocytogenes:Since there has been increasing involvement in the presence or absence of Listeria Monocytogenes in nutrients, as a consequence of some significant eruptions of nutrient borne listeria meningitis in North America and Europe, there has been a critical demand to develop methods to insulate it in assorted type of nutrient. Several methods such as ELISA, PCR and familial hybridisation engineerings ( Entis and Lerner, 1991, RMR Labs, 2000, enfranchisement, Report, 2000 ; Klein and Juneja, 2001 ) have been developed.Department of agribusiness ( USDA ) and the Food and Drug Administration ( FDA ) , are the two US bureaus that made usage of different protocol for analysis of Listeria Monocytogenes.
The techniques for isolation of Listeria Monocytogenes affect two- phase enrichment, the pre-enrichment followed by enrichment and plating for isolation.The enrichment procedures helps to maintain the degree of polluting micro-organisms to a sensible Numberss and allow generation of Listeria Monocytogenes to degrees that are adequate for sensing of the being. Half Fraser Broth and the University of Vermont broth ( UVM ) are illustrations of stocks for the pre-enrichment processs. They allow resurgence of injured Listeria cells. The Fraser stock is used with a selective Fraser broth addendum in enriching for the enrichment stairss after the pre-enrichment and for observing Listeria.
Both the Fraser and Half Fraser Broth contain sodium phosphate and K phosphate which are buffering agents. The presence of ferrous ions acts as an index since the bacteriums produces 6, 7- dihydroxycoumarin that reacts with the ferrous ions therefore ensuing in the darkening of the medium. Lithium chloride, nalidixic acid and acriflavine give the stock a higher concentration of salt and inhibit growing of enterococci.However, it is merely after 48 hours that there is melanizing of the stock.For plating, PALCAM, Oxford and Modified Oxford ( MOX ) are used as selective agars for isolation of Listeria Monocytogenes. Lithium chloride, polymyxin B sulfate and acriflavine HCl, nowadays in the PALCAM medium Base and ceftazidine found in the PALCAM addendum guarantee the selectivity of the medium. These elements suppress other bacteriums present in nutrient except Listeria.For distinction, the PALCAM medium provides esculin and Osmitrol.
Hydrolysis of esculin by Listeria causes production of 6, 7, dihydroxycoumarin, which reacts with the ferrous ions that are present in the PLACAM medium to organize blacken aura.USDA method:The USDA method involve a two- phase enrichment process with a 24-48 hours primary enrichment with UVM medium followed by a 2nd enrichment stage with Fraser stock. Black settlements on the MOX plates show the presence of Listeria Monocytogenes.FDA method:This method involves 48 hr enrichment at 30A°C in buffered Listeria Enrichment Broth ( BLEB ) . Pre enrichment process is optional which is done 4 hours at 30A°C prior to the add-on of the selective addendums. After 24 hours to 48 hours the civilization is streaked onto Oxford, PALCAM, Lithium chloride-phenyl ethyl alcohol moxalactant ( LPM ) . After 24-48 hours at 30A°C, black-halo settlements prove the presence of Listeria.ISO method:The ISO method and the USDA method are likewise with merely the difference of utilizing Half Fraser Broth for enrichment in the ISO method.
The enrichment is done utilizing Fraser Broth. On PALCAM or Oxford agar, the Listeria settlements are grey green with the black aura and black severally.Deoxyribonucleic acid extraction:As the phylogenic or the population genetic sciences research is increasing, genomic DNA isolation from populating stuff such as bacteriums, Fungis, workss, insects, carnal cells and blood is of import.The conventional method of DNA extraction involves 3 stairss viz.
:Lysis of cell wall or cell membrane.Removal of all unwanted content fro illustration proteins, polyose and lipoids.Recovery of DNA.Gram positive bacteriums such as Listeria Monocytogenes has thick cell walls composed of peptidoglycan which is stiff, therefore doing it hard to interrupt down the cell wall.
Therefore of import intervention which involves the usage of muramidase, osmotic daze, detergent, boiling extraction is carried out. Commercial kit besides available on the market is used for DNA extraction.Molecular method for sensing of Listeria Monocytogenes:Frances.
P.D and Keith.I stated “ Methods for subtyping Listeria can be separated into two wide classs: ( a ) concentional methods, which include serotyping, phage typewriting, and bactteriocin typewriting and ( B ) molecular methods, which encompass multilocus enzyme cataphoresis ( MEE ) , chromosomal DNA limitation endonucleases analysis ( REA ) , ribotyping, DNA macrorestriction analysis by pulsed- field cataphoresis ( PFGE ) , random elaboration of polymorphous DNA ( RAPD ) by PCR, and DNA sequence-based subtyping. ” ( 2001 ) .
RFLP ( restricted fragment length polymorphism ) forms portion of the molecular method for subtyping ( Emily.T.yeh, 2004 ) .Note: for this experiment RAPD PCR and RFLP was carried out to measure the familial relatedness of the isolates of Listeria Monocytogenes.PCR methods:In 1983, the debut of PCR has been revolutionized the microbic ecology and has been of increasing usage in nutrient microbiology.
The polymerase concatenation reaction makes usage of enzymes to magnify 1000000s of transcripts of mark Deoxyribonucleic acid in few hours. “ PCR today plays a cardinal function in familial typewriting of beings or persons and molecular epidemiology ( Viljoen, G.J et al. , 2005 ) .However, false positive consequences may be obtained if the PCR reaction is contaminated by populating cells since the PCR can magnify both sequences from both life and non life cells.
( Malorny et al. , 2003 )Restricted fragment length polymorphism ( RFLP ) :“ one of the most normally used tools for following the heritage of cistrons or cistron markers is that of the linked Restriction Fragment Length Polymorphism ( RFLP ) ” stated by M.J.
McPherson, et al.,1991.The chief technique involve in RFLP is doing usage of enzymes to digest the targeted DNA into different little fragments.
Separation of the fragments is done by gel cataphoresis and comparing is done utilizing a investigation.In many epidemiological probes, RFLP has been successfully used. However, to compare and separate between isolates of closely related strains, a greater sum of DNA sample can non be used to hold a maximal fluctuation. ( G.Roger, 2005 ) .