the study of listeria monocytogenes Essay

Listeria is considered a rare but potentially dangerous disease. Furthermore, it is an deviant bacteria since it can turn at low temperatures of below 5. This information is supported by the work of Health Protection Agency ( 2010 ) . Listeria genus consists of gm positive rods, non-spore forming, facultative anaerobic, regular rod shaped bacteriums. Seegler and Jones ( 1986 ) agree with these features and add that Listeria genus is non-capsulate in nature. It was further stipulated that they ( Listeria ) are catalase-positive, oxidase-negative and motile at 20-25 based on the peritrichous scourge but non-motile at 37. This information is supported by the work of Winn and Koneman ( 2006 ) . Furthermore, it has been stipulated that the genus is defined by a G + C DNA content of 36-38 % , a typical gm positive cell wall which has a peptidoglycan murein bed incorporating meso-diaminopimelic acid ( meso-DAP ) attached to the cell membrane by lipoteichoic acid, and membrane associated polyribitol teichoic acids. Listeria belongs to the household, Listeriaceae.

With regard to its pathogenicity, Listeria is chiefly restricted to two species. These species are L. monocytogenes and L. ivanovii. This information is supported by the work of Downes and Ito ( 2001 ) . It was stated farther that one of the species ( strains ) , Listeria monocytogenes, is responsible of about all issues related to human listeria meningitis and in approximate, 90 % of listeria meningitis instances affecting animate beings, with L. ivanovii seen as the less deadly and of most concern in animate beings.

The genus, Listeria is believed to be made up of six species. These species are Listeria monocytogenes, Listeria ivanovii, Listeria welshimeri, Listeria innocua, Listeria seeligeri and Listeria grayi. This information is supported by the work of Racourt ( 1999 ) ; Vazquez-Boland et al. , ( 2001 ) . Furthermore, it was stipulated that apart from Listeria monocytogenes and Listeria ivanovii which are known to be infective, the staying species are considered non-pathogenic.

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Listeria monocytogenes is a gram positive facultative intracellular pathogen that has the ability of doing chronic food-borne infections in worlds, therefore ensuing to 20 to 50 % mortality in vulnerable populations, such as yearlings, the aged and immuno-compromised individuals. This information is derived from the work of Huang et al. , ( 2006 ) . This being was antecedently known as Bacterium monocytogenes. This information is derived from the work of Nyfeldt ( 1929 ) . Fischetti ( 2006 ) concurred with the fact that Listeria monocytogenes are gram positive bacteriums but added that they are later bacillar and non-sporulating in nature with the ability to assume different mammalian cells in order to boom in the cytosol of these host cells and to propagate into near-by host cells. The dimension of the non-sporing rods is about 0.5m in diameter and 0.5-2.0m in length. This information was derived from the work of Seeliger and Jones ( 1986 ) . Harmonizing to Fang et al. , ( 2004 ) it is claimed that Listeria monocytogenes are usually found in nutrient merchandises such as fresh meat and domestic fowl, processed ready-to-eat meats, sea nutrient, soft-style cheeses and butter. Furthermore it is stipulated that their being is as a consequence of their ability to boom good and turn at fortunes related to normal processing and distribution of nutrient, such as infrigidation temperatures, tremendous Na chloride concentrations or H2O activities every bit low as 0.92. Apart from being able to develop at infrigidation temperature, L. monocytogenes has the capacity to defy heat and salt efficaciously. Apart from nutrients, Listeria monocytogenes were foremost isolated from tissue of patients in Germany in 1891. Subsequently other hosts of Listeria monocytogenes have been liver of coney and spinal fluid of meningitis patients sometime ago thought to be in the twelvemonth 1911 and 1917 severally. This information was sourced from the work of Reed ( 1958 ) ; McCarthy ( 1990 ) as cited in World Health Organization ( 2004 ) . Harmonizing to Murray et al. , ( 1926 ) , Listeria monocytogenes was non merely isolated from coneies but besides guinea hogs of which the being ( L. monocytogenes ) was observed to do monocytosis in the septic animate beings.

Harmonizing to Schuchat et al. , ( 1991 ) as cited in Goldfine and Shen ( 2007 ) , Listeria monocytogenes are relevant causes of zoonotic diseases, particularly in herb animate beings. It was further stipulated that apart from these bugs, Listeria monocytogenes, being found in nutrient merchandises, they can later be found in dirts. These bugs can besides be found in disintegrating flora.

World Health Organization ( 2004 ) claims that Listeria monocytogenes is an timeserving pathogen which chiefly affects those with a chronic implicit in frailty or status ( e.g. immunosuppression, HIV/AIDS, chronic conditions such as cirrhosis that defect the immune system ) ; pregnant adult females ; unborn or freshly born delivered babies ; and the aged. Unlike Listeria innocua, which are seen as the non-pathogenic coinage of the genus, Listeria, they are utilized as foster micro beings in detecting and analyzing the growing and survival features of Listeria monocytogenes. This information is supported by the work of Glaser et al. , ( 2001 ) as cited in World Health Organization ( 2004 ) .

Listeria monocytogenes is known to incorporate a cell wall formed by a multi-layered cross linked peptidoglycan decorated with teichoic and lipoteichoic acids. The cell wall of Listeria monocytogenes has an tremendous duty, physiology wise, in guaranting unity of the cell while keeping a high internal osmotic force per unit area. Furthermore, the cell wall is known to give the cell a precise cell form and supply protection against mechanical emphasis. The cell wall every bit acts as a scaffold which allows different proteins to joint to it. This information is supported by the work of Goldfine and Shen ( 2007 ) .

Harmonizing to Fischetti ( 2006 ) , based on the pathogenicity of Listeria monocytogenes, they are known to infect domestic animate beings and worlds by deriving entry into the bowel ; hence distributing quickly to deeper variety meats which could take to infrequent, but rarely lifelessly frailty. Harmonizing to Downes and Ito ( 2001 ) , the sequence in which Listeria monocytogenes causes disease can be categorised into three stages. The first stage involves the consumption of beings ; while the 2nd phase involves the extract of the GI liner, this is followed by reproduction after undergoing phagocytosis through macrophages. The 3rd stage involves the lysis of the macrophage, which advances to the blood poisoning and usurping of assorted mark variety meats, including the placenta and cardinal nervous system ( CNS ) . However, for L. monocytogenes to be able to do unwellness, it must boom in the tummy which has an acidic encompassment. Apart from lasting the sourness of the tummy, it besides should hold the ability to perforate the enteric liner and grow in the host.

Chilled nutrients are termed as ready-to-eat nutrients which contain natural or uncooked condiments. These condiments are the likes of cheese or salad. This information is supported by the work of Stringer and Dennis ( 2000 ) . Furthermore, their manner of readying is such that the nutrient is either evident to consume or requires partial cooking instead than full cookery before use. In most instances these peculiar nutrient types have the inclination to be risky and deadly since it requires partial cooking bearing in head that Listeria monocytogenes which is the causative agent can defy cold but heat efficaciously. On the other manus, ready-to-eat nutrients can every bit be referred to as cooked nutrients intending that the whole nutrient condiments are cooked which should miss the presence of Listeria monocytogenes as a consequence of their ( L. monocytogenes ) non-heat immune position.

With regard to the illustrations of chilled nutrient, they are as follow:

Butters and Spread



Jacket murphies

French friess

Sausage axial rotations



This information was derived from the work of ‘Rew Valley Dairies ‘ ( 2010 ) .

Different storage temperatures are required in hive awaying ready-to-eat chilled nutrients. In tabular signifier, different storage temperatures at which most influential European states adopt are as follows:


Chilled Storage


Max 7




Meat based merchandises: 6 ; other chilled merchandises: 8


Storage at 4


Meat merchandises: -1to 7 ; fish merchandises: 0 to 4





The Netherlands

Max 7

United Kingdom

Max 8

This tabular array was sourced from Stringer and Dennis ( 2000 ) .

Sandwich is regarded as a simple and unsophisticated nutrient that in clip immemorial was discovered foremost in the Middle East, around 9000 BC. Its find was about the clip civilisation kicked into being. This information is derived from the work of Mercuri ( ) . It was further stipulated that the find period is still under argument as the English claim of detecting sandwich.

Sandwich consists of one or more pieces of staff of life with delightful and alimentary filling between them. With regard to the bread-type, staff of life, pick or loaf staff of life, axial rotations and buttockss will do a good sandwich. This information was derived from the work of ‘Hub pages ‘ ( 2010 ) . It was further stipulated that the filling may be pieces of cold meat, chopped meat, eggs, poulet, jambon and cheese with creamed butter, pickles, tomato ketchup or mayonnaise. Furthermore, sandwiches are divided into six types. These are:

Open Sandwichs: Here, this sandwich-type consists of one bread-kind with make fulling on top. The form of the staff of life in inquiry is normally square, triangular or unit of ammunition. This sandwich type is normally garnished with pieces of carrots, raisins, pickles, as the chief fillings are butter, pieces of cheese and meat fillings.

Plain Sandwichs: A field sandwich is made up of two pieces of staff of life, chiefly a day-old staff of life, of which butter or mayonnaise is used as spread to non merely to add spirit on the sandwich but besides to do the sandwich more alimentary.

Pinwheels Sandwichs: These sandwich types are made of pick staff of life sliced length wise, approximately 3/8 inch midst. Fresh pick staff of lifes are preferred to non-fresh pick staff of lifes since they are easy to turn over and will non check. The spreads are chiefly softened butter or oleo, creamed cheese, marmalade, cheese sweet pepper, peanut butter, jams and gelatins.

Closed Tea Sandwiches: This type of sandwich requires enormous sum of infrigidation. They are usually removed from the deep-freeze three hours before they are served. The form of the sandwich is could be square, rectangular or oblong. Here, butter is spread on one side of the staff of life and the fillings are placed on the other half. This sandwich type is usually placed in waxed paper or in a clean moistness towel and placed in a vacuity before frozen.

Ribbon Sandwiches: This sandwich type is made up of colored pick staff of life. Here 3 slice each of pink and green staff of life with one or more feelings spread between pieces. The stack of pieces is compressed together and the crusts are trimmed.

Mosaic Sandwichs: The initial measure is synonymous to that of the thread sandwiches but here the 3 thread sandwiches are stacked so that green and pink subdivisions alternate themselves wholly.

In respects to the legal demands of nutrient samples incorporating Listeria, the bug is categorised safe if a certain sum of it is present in a nutrient sample. Depending on the sum of nutrient ( in gm ) , the settlement organizing units of Listeria differ. In other words, for every gm, there is an acceptable degree of settlement organizing units. For illustration, legion degrees of Listeria monocytogenes ( cfu per gm ) show a failure with nutrient handling controls and with respects to show epidemiological grounds are considered a public wellness hazard. This information is derived from the work of ICMSF ( 2001 ) . It was further stipulated that the presence of Listeria on nutrient is as a consequence of insufficiency in the cookery technique adopted or as a consequence of abysmal station readying practises adopted. Harmonizing to Toldra ( ) , the purpose of the committee ordinance is to relieve Listeria sum instances in worlds. Not merely Listeria is aimed at but besides Enterobacter sakazakii and Salmonella. Furthermore, it was stated that the cardinal constituent of the Regulation is to put two different types of standards for nutrient stuffs which need to be documented by nutrient concern operator. These standards include:

A nutrient safety standard specifying safety of a merchandise or a batch applicable to merchandises placed on the market.

A procedure hygiene standard demoing the right operation of the fabrication procedure.

The microbiological Criteria Regulations are legal ordinances that set specific regulations for the testing of certain nutrients for relevant disease organisms. This information is derived from the work of alcontrol research labs ( 2010 ) . Tompkin ( 2002 ) , microbiological standard is defined as the acceptableness of a merchandise or a nutrient batch, based on the absence or presence or sum of micro beings, including parasites, and/or measure of their toxins/metabolites, per unit ( s ) of mass, volume, country, or batch.


Microbiological standards can be categorized into three even though Codex recognizes merely one class.

Microbiological Standard: This is seen as a compulsory standard that is added into a jurisprudence or regulation.

Microbiological Guideline: This is seen as an consultative standard utilized to advise nutrient operators and others of the microbic content that can be expected in a nutrient when best patterns are applied.

Microbiological Specification: This standard may be compulsory or consultative depending on usage. It is seen as portion of a buying Concord between a purchaser and a provider of nutrient.

Harmonizing to National Research Council ( ) , the microbiological standards were detailed. These include:

For Standard, a microbiological criterion is a microbiological standard that is a portion of jurisprudence, regulation, or administrative ordinance. Since a criterion is a mandatory standard, failure to follow with it consequences to jurisprudence, regulation, or ordinance noncompliance and this will be capable to the enforcement policy of the regulative bureau holding legal power.

For a microbiological guideline, this standard is frequently utilized by the nutrient industry or a regulative bureau to oversee a fabrication procedure. Guidelines operate as qui vive mechanisms which gives a precursor as to whether microbiological status wining at critical control points or in the finished merchandise are within the normal scope. Subsequently, microbiological guidelines are utilised to measure processing efficiency at critical control points and conformance with GMP ( Good Manufacturing Practices ) . Besides, microbiological guideline is an consultative standard in that a given batch of nutrient transcending the bound for a non infective being would non be taken off the market or even downsized. Guidelines sometimes could be mandatory merely like standard standard in the sense that nutrient company direction and regulative bureaus may demand that the conditions responsible for uninterrupted microbiological lacks be corrected without cunctation.












Give Examples








1 LISTERIA- FOCUS L.monocytogenes

What it is

Illnesss ( Including epidemiological informations

Food linked with L. monoctytogenes ( )

2 Legal demands

-Micro standards regulstions

Duty of maker to supervise

Ph / H2O activity bound to l.mono growing

3 sandwiches

Components- tomatoes- pH


Water activity

Temperature- chilled

Short shelf life

Purposes and aims