Main Genus Characteristics Of Listeria Biology Essay

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Listeria was firstly isolated from rabbit liver, in which it caused tissue necrosis, by Prof. Hülphers. First publication describing Listeria was Murray and coworkers, in which was isolated bacterium causing spontaneous lethal disease among rabbits in Cambridge University animal breeding (Murray 1926). Pirie (Pirie 1927)isolated a new bacterial species, named Listerella hepatolytca honouring Lord Lister, form some clinical cases among South Africa gerbils. After examination of both isolates at Lister Institute in London, high similarity between both isolates was determined and this bacterium was so called Listerella monocytogenes, later corrected in Listeria because of former attribution of Listerella to another bacterium. Clinical history of L. monocytogenes was from sheep (Gill 1933) and then in a human patient in 1929 (Nyfeldt 1929)

Main genus characteristics

Listeria is a Gram positive rod-shaped, round-ended and non-sporing bacterium, which is motile at 20-25°C because of peritrichous flagella (flagella motility is not active at 37°C) and is facultative anaerobic. Cells can be found single or aggregated in short chains. On nutrient agar, this microbe form smooth, puntiform and traslucent round colonies. After 24 hours of incubation colonies have a glistening surface (S-form), while longer incubation give colonies slight roughness (R-form). Exposure to light obliquely transmitted give to colonies a blue-green appearance, whereas they seem bluish-gray under normal condition of illumination. For its morpholocial appearance, Listeria has been long included in the bacterial group of coryneforms, even if molecular methods recently developed allowed to give a more clearly defined position. Within this genus it is possible distinguish, from a biochemical point of view, five diverse bacterial species: L. monocytogenes, L. innocua, L. ivanovii (Dongyou 2008), L. welshimeri, L. seeligeri and L. gray. There is also a seven species mentioned within this genus, Listeria murray, which has been defined as a subgroup of L. gray through molecular investigations (DNA-DNA hybridization, multilocus enzyme electrophoresis, and rRNA restriction fragment length polymorphism) (Rocourt 1992). Of all mentioned species only L. monocytogenes and L. ivanovii harbor virulence properties causing disease in human and animal hosts, respectively. Biochemical properties of all them are reported in table. Listeria monocytogenes can grow in most of laboratory media with pH ranging from 4.3 until to 9.4 (Ottaviani, Ottaviani e Agosti 1997). Minimal aw for growth has been reported to be 0.90. Growth temperature cover a quite wide range from -1,5 to 45°C, even if low temperature increase time of lag phase: this property is often exploited in cold enrichment isolation procedure (Hansen, Gerner-Smidt e Bruun 2005). Optimal temperature is considered 30-37°C. L. monocytogenes is able to grow in presence of CO2 even at low temperature, but CO2 concentration higher than 70% could inhibit its growth if temperature is less than 7°C (Wimpfheimer 1990). Because of its ability to grow in so wide-ranged parameters of growth, L. monocytogenes is considered widely and ubiquitary distributed in the environment, making difficult defining its ecological niche. Listeria posseses survival capacity in presence of 10% NaCl and 200 ppm NaNO2, as well as in moist and dry environments at specific sites within food manufacturing environments for years. Even when present at high levels in foods, spoilage or taints are not generally produced. L. monocytogenes do not show relevantly high thermal resistance and is not able to resist to milk pasteurization : its D values (decimal reduction times) range from 16.7 to 1.3 min at 60°C and 0.2 to 0.06 min at 70°C (Dongyou 2008).

L. monocytogenes

L. ivanovii

L.- seeligeri

L. innocua

L. welshimeri

L. gray

Gram staining

+

+

+

+

+

+

Catalase test

+

+

±

+

+

+

β-hemolysis

+

+

+

-

-

-

CAMP test

Staphylococcus aureus

+

-

+

-

-

-

Rhodococcus equi

-

+

-

-

-

-

Acid production starting from

esculin

+

+

+

+

+

+

maltose

+

+

+

+

+

mannitole

-

-

-

-

-

+

xylose

-

+

+

-

+

-

rhamnose

+

-

-

v

v

±

α.methyl-D-rhamnoside

+

-

±

+

+

±

Virulence in mice

+

+

-

-

-

-

Serotype

1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4a, 4ab, 4b, 4c, 4d, 4e, 7

5

1/2b, 4c, 4d, 6b

6a, 6b

6a, 6b

Tab. 1‑1: Bioichemical traits of interest of bacterial species within Listeria genus. +, positive reaction; -, negative reaction; ±, variable or weak reaction (Ryser 1999).

Listeria infections: clinical description

Listeria infections can occurs in almost all domestic animals, even if the most common host is the ruminant. Monogastric animals can be susceptible to the microorganism, even if it is a rare event mainly manifested as septicemia, while the main symptoms in animals can be summarized in encephalitis, septicemia and abortion (3) with the possibility to excrete the pathogen through the milk, whose incidence has been associated with indoor housing and silage feeding, and poor hygiene procedure application.

In humans L. monocytogenes can provoke both a noninvasive and invasive form of illness. Non-invasive kind of listeriosis can affect even healthy adult individuals, but there is still a lack of knowledge about infectious dose and properties and interactions of organisms and host remain unclear. Characteristic symptomatology involve gastroenteritis, fever, diarrhea and vomiting with an average incubation time of 18-20 hours. Related frequency is extremely variable and it is often possible that pathogen can be present in human host without any apparent symptoms, fact which make difficult to diagnosticate the sickness in hospital. In its invasive form of sickness, because of ability of microorganism to migrate through placenta, Listeria monocytogenes can lead in pregnant women to spontaneous abortion, stillbirth or severely ill baby birth. Further source of its diffusion could be attributed to acquisition from newborn due to post-natal infection of mother or other infected babies. Usually mother are rarely exposed to severe symptoms, because pathogen prefers focusing on fetus due to its higher sensitivity.

Listeriosis can affect also healthy and non-pregnant subjects, among whom the most sensitive group is composed of immunocompromised and elderly because of the reduced effectiveness of their immune system. Listeriosis, in this group of patients, has been present meningitis and septicemia. Incubation time usually cover a time period of one day until several weeks. There is still few knowledge about infective dose, which can vary among patients. Generally there are defined three main possible routes of listerial contamination:

Contact with animals: wild animals, as well as domestic ones, can carry this pathogen and most of them can manifest symptoms of listeriosis. Septicemia and abortion are frequently encountered in sheep and other animals and disease can be transmitted to human hosts: in this case infection assumes the form of skin infection in people exposed to direct contact with animals (e.g. farmers and veterinarians) and express mild form of self-resolving symptoms, although it cannot be excluded the possibility of evolution in more severe forms.

Cross-infection of newborn in hospital: listeriosis is reported as cause of 29 incidents in UK with a 25% of late onset of neonatal cases.

Foods: majority of reported episodes, especially outbreak episodes, has been related to ingestion of food contaminated by L. monocytogenes. and will be more extensively discussed in further pages.

1,381 confirmed cases of listeriosis were reported in 2008. The number of confirmed cases of listeriosis (Tab. 1 -2) decreased slightly when compared with reported cases concerning 2007. Listeriosis mainly occurred among elderly people (55.2% of cases took place in individuals over 65 ages). The second highest notification rate was with regard to children under the age of five (0.4 cases per 100,000 population). The case fatality rate for human listeriosis was 20.5%, whose highest value in terms of incidence in selected groups of population was found among the elderly (Fig. 1 .1). The EU notification rate was 0.3 per 100,000 population with highest notification rates observed in Denmark, Finland and Sweden (EFSA 2010).

Fig. 1.1: Age-specific distribution of reported confirmed case s of huma n listerios (EFSA 2010).

Tab. 1‑2: Reported listeriosis cases in humans 2004-2008, and notification rates for confirmed cases in 2008 (EFSA 2010). Total number of cases are reported concerning 20004, while for 2005-2008 number of confirmed cases is reported. A: aggregated data report; C: case-based report; -: No report; U: unspecified.

Listeria monocytogenes infectious cycle

In order to ensure a more complete view, here is briefly summarized the whole process of host colonization. After ingestion of polluted food, L. monocytogenes is exposed to highly adverse environmental conditions (proteolytic enzymes, low pH of stomach, bile salts and inflammatory attacks), to which the pathogen can withstand thanks to stress response-related genes and proteins (Hamon 2006). Subsequent steps are adhesion and internalization of host through internalins: this group is composed of surface proteins, among which InlA and InlB are worth of a special mention, facilitate invasion in host tissues evasion from host immune system during its surveillance activity.

Fig. 1.2: From saprophyte to intracellular pathogen. Listeria monocytogenes survives in a diverse array of environments, in habitats that include soil and water as well as food processing facilities. Central to the switch between life outside and life inside mammalian hosts is the transcriptional activator PrfA, which regulates the expression of many gene products that are required for bacterial virulence. Outside a host cell, PrfA exists in a low-activity state, with correspondingly low levels of virulence gene expression. Once inside the host, PrfA becomes activated (PrfA*) and induces the expression of gene products that are needed for host cell invasion (internalins InlA and InlB), phagosome lysis (listeriolysin O (LLO), phosphatidylinositol-specific phospholipase C (PI-PLC) and phosphatidylcholine (PC)-PLC), intracellular growth (hexose-6-phosphate transporter (Hpt)), and cell-to-cell spread (actin assembly-inducing protein (ActA); actin polymerization is shown in turquoise) (Freitag 2009).

At this point pathogen can be located in cell vacuole, from which mic robe can escape through lysis factors (listeriolysin O or LLO and phosphatidylinositol-phospholipase C or PI-PLC), and then in cellular cytosol, where it can grow and multiplicate. Further steps consist in propelling toward cytoplasmatic membrane (this action is mediated by ActA which lead to polarized actin tails enabling intracellular motility) and formation of envelopes for spreading infection in adjacent cells and beginning of a new infection cycle (Freitag 2009).

Molecular properties of interesting

L. monocytogenes has been subjected to notable evolutionary process leading to acquisition of a collection of molecular functions and determinants, which have played a contributory role in successful spreading and environment colonization as intracellular pathogen. Virulence-associated genes previously mentioned can be found in a 9.6 kb single chromosomic location, pathogenicity island, which is regulated by suitable regulation factor, PrfA, whose correlated gene is collocated immediately downstream the virulence cluster and activates trascription of other molecular determinants virulence-related. Beside these genetic function, other genes, like invasin associated protein or iap, are reported as associated to expression of potential pathogenicity.

Fig. 1.3: Genetic structure of the chromosomal region of the hly virulence gene cluster (LIPI-1) in Listeria spp. Genes belonging to LIPI-1 are in green (the more divergent actA gene is hatched) (J. K.-B.-Z. Vàsquez-Boland 2001).

hly The L. monocytogenes hemolysin, listeriolysin 0 (LLO) is the best described protein related to L. moncytogenes virulence. It belongs to sulfhydryl-activated pore-forming cytolysins protein family. Its role is mediating lysis of bacterium-containing vacuoles, after that bacterium is able to grow and multiuply in host cytoplasm, using cytoplasm itself as growth medium.

pleA Adjacent to hly and transcribed divergently, there is a gene which encodes a phosphatidylinositol-specific phospholipase C (PI-PLC) , whose function could be summarized in hydrolysis of both PI and PI-glycan. The plcA sequence shows predicts 30% amino acid identity with Bacillus thuringiensis and Bacillus cereus PI-PLC. Interestingly other gram-positive bacteria such as Staphylococcus aureus, Clostridium novyi, and Bacillus anthracis also possess PI-PLC activity.

prfA. This gene encodes for a protein that is responsible for regulating itself and other virulence-associated genes (i.e., plcA, hlyA mpl, actA, and plcB). prfA is the second gene of an operon and can be expressed either from its own promoter located in the pkcA-prfA intergenic region or from the plcA promoter, suggesting that prfA regulates its own synthesis. Whether the prfA gene product acts directly on all of the genes under its control has not been demonstrated, but in B. subtilis, the prfA-encoded gene product directly activates the transcription of hly. In addition, it was hypothesized that PrfA may recognize a 14-bp palindromic sequence found in the -35 region of the promoters for hly, picA, and mpl, suggesting that this palindrome may be the target site for PrfA-mediated activation. PrfA gene is present in all serovars of the pathogenic species L. monocytogenes and expression of prfA-regulated genes is thermoregulated (Vàsquez-Boland, et al. 2001).

Relevant aspects of Listeria monocytogenes concerning food processing environments

Tolerance to adverse conditions and antimicrobial resistance

Being a facultative anaerobe, L. monocytogenes can grow in vacuum- or modified atmosphere packaged foodstuffs (Buchanan et al. 1998). Temperature optimum determined through culture monitoring has been resulted 30-37°C, but this microbe can multiply at refrigeration temperature and survive during frozen storage. Temperature upper limit was defined as 45°C and pasteurization at 71.6°C for 15s can reduce notably bacterial contamination. L. monocytogenes can cover a large pH range from 4.3 until to 9.6 with optimum in neutral or moderately alkaline values. Growth Minimal aw is located at 0.90, even this bacterium has demonstrated high tolerance for high osmotic pressures.

The ability of this bacterium to grow at refrigeration temperatures makes L. monocytogenes a postprocessing contaminant in long-shelf-life refrigerated foods. The widespread distribution of L. monocytogenes and its capability to survive on dry and moist surfaces favors post-processing contamination of foods from both raw product and factory sites (McLauchlin 1996). In addition, Listeria spp. also show unusual tolerance to high salt concentrations (up to 10% NaCl and sodium nitrite). The capacity of L. monocytogenes to withstand severe environmental stresses depends on its efficient stress response mechanisms: various salt stress response genes (including betL, gbuABC, opuC, opuB, lmo1421, and bsh) have been characterized, a majority of which are regulated by an alternative sigma factor, σB (encoded by sigB)-a protein subunit of RNA polymerase (RNAP). Mutations in sigB and related genes result in lower acid and salt tolerance in L. monocytogenes. Further, σB also influences L. monocytogenes virulence gene expressions by co-regulating a pleiotropic virulence regulator gene, prfA. A number of L. monocytogenes genes expressed in response to growth at low temperature have also been identified. However, although Listeria spp. are known to tolerate alkali and pressure well, the underlying mechanisms against these stresses are poorly understood.

Sanitizers conventionally employed in food processing plants has shown good effectiveness in reducing population density, even if it possible establishment of adherent communities can lead in improved tolerance against biocide molecules. Exposure to antimicrobial could also induce adaptation and cross-resistance to other bactericidal agents (further disinfectants and/or antibiotics): antibiotic and biocide antibacterial actions reveal strong similarities concerning target action mechanism and/or clinical aspects (like uptake through passive diffusion, effect structural changes of membrane and/or effect on diverse key steps of bacterial metabolism). In presence of toxic agent or stress source, response/adaptation of bacterial cells take place activating some similar defense mechanisms to confer resistance against structurally non-related molecules. Mechanisms possibly involved could be generally grouped into two main categories:

Intrinsic resistance represent an innate trait conferred by the bacterial genome and applied strategies include impermeability, efflux, biofilms and/or transformation of toxic compounds. In order to decrease intracellular amounts of harmful molecules, Gram negative bacteria can modify permeability through limiting synthesis of porines, which are pore-forming proteins across the whole thickness of cell membrane and altering the lipopolysaccharide structure (Nikaido 2003, Poole et al. 2002a). Another mechanism implies overexpression of efflux pumps (protein complexes capable to expel antibiotics) (Poole 2007). Acquired resistance takes place because of mutations and acquisitions of mobile genetic elements (transposon, plasmids) coding for resistance-related proteins (enzyme, transporter). Similarly, the acquired processes may protect against antibiotics and biocides (Maillard 2007). In addition, some of the mechanisms that play a major role in resistance are controlled by diverse genetic cascade regulations that share common gene regulators (soxS, marA) (SCENHIR 2009, Poole 2002)).

Contamination of raw materials

Other causes of concern are related to its ubiquitous presence in environment and the possibility of its isolation from a wide range of raw foods: Beuchat (1996) has demonstrated presence of this bacterium in sewage, soil, decaying vegetation, silage, plants in both cultivated and uncultivated areas, feces of wild and domestic animals, and wildlife feedings grounds. Because of its widespread presence in natural environments and in animals, which can vary depending on species and country [as shown in Tab. 1 -3 (EFSA 2010), L. monocytogenes could be introduced in initial phases of food processing. Highest levels are reported especially for sheep, even if similar incidence could be found in goats or in cattle. This could be translated in high probability of introduction of L. monocytogenes in initial phases of food supply chain. Milk and slaughterhouses offer a good instance.

Despite low prevalence (Meyer-Broseta, et al. 2003), L. monocytogenes is often found in animals, both sick and healthy (Fthenakis, et al. 1998, Wagner, et al. 2000), although contamination from animals is not the main routes: actually it could be better talking of multisource contamination due to the contribution from environment and poor hygiene practices applied (Hassan, Mohammed e McDonough 2001, Sanaa, et al. 1993). Prevalence in slaughterhouses has been associated to alive livestock due to its presence in faces, tonsils and hide (Buncic 1991), even if variation in strain predominance and prevalence in Listeria spp. and Listeria monocytogenes environmental isolates population has been shown related to diverse hygiene quality (Borch e Christensen 1996, Saide-Albornoz, et al. 1995). Listeria can be isolated also in acquatic environments, even if this kind of source does not represent natural niche for this microorganism.

Tab. 1‑3: Listeria spp. and L. monocytogenes in animals, 2008 (EFSA 2010)

Tab. 1‑4: Compliance with L. monocytogenes criteria laid down by Regulation (EC) No 2073/2005 in food categories in the EU, 2008 (EFSA 2010).

L. monocytogenes on food processing equipment

L. moncytogenes has been reported as a contaminant of food processing tools in different sectors of food supply chain (dairy, fishery, meat and poultry), but it is a more probable contaminants of several non-food contact surfaces, including walls, doors, trucks and/or shoes (Fonnesbech Vogel, et al. 2001, Miettinen, Aarnisalo e Sjöberg 2001, Norton, et al. 2001, Suihko, et al. 2002). Also contamination of processing equipment is notably diversified, ranging from tanks and conveyors until to slicing and packaging apparatus. Main common characteristic of mentioned surfaces is presence of narrow openings and hard-to-reach sites, which make difficult and inefficient sanitation procedures leading to presence of the pathogen even on treated surfaces. Temperature seems conditioning presence of this food-borne pathogen on the above mentioned facilities: L. monoctogenes is more abundant at low environmental temperature than high corresponding one, where competitive microflora grows at higher level and heterogeneity. Also kind and status of material could play an important role: smooth stainless steel surface are less easy to be colonized by L. monocytogenes than damaged and/or rough plains (Chasseignaux, et al. 2002).

Abundance in foods

There is a wide diversity in harboring Listeria and L. monocytogenes among foods with heterogeneous abundance within a certain tipology. In dairy products cheese, with special mention regarding soft cheeses, are the one with highest Listeria prevalence ranging between 0 and 30%, while fish and fishery derivatives are less frequently associated with this microorganism, compared to meat or dairy, but show an higher prevalence (0-50%): within this typology Listeria contamination interests particularly not termically treated such as cold smoked salmon, whereas heat-treated foodstuffs show listerial contamination less than 12%.

Also quantitative amount of contamination is worth of being mentioned: if admitted presence in foodstuffs at time consumption is put at 100 CFU/g, several reports throughout Europe have reported levels above this limit: Nørrung et al. Have reported level higher than 100 CFU/g in 1.3% of heat-treated meat products and in 0.3-0.6% of conserved meat and fish derivates in years 1994-1995 and1997-1998, respectively (Nørrung, Andersen e Schlundt 1999, Goulet, et al. 2001), while in other more limited studies 0-1% was reported as containing more than 100 CFU/g (Rørvik e Yndestad 1991, Harvey e Gilmour 1993, Jemmi, Pak e Salman 2002). Interesting aspects are also related to measurement of food safety control measures applied in European countries, which have allowed to decrease significantly listerial presence in foods. However, these procedures must be performed systematically and periodically in order to keep under control this food-related risk.

Tab. 1 -5 shows that the highest levels of non-compliance at retail was observed in RTE fermented sausage (0.5%) and RTE fishery products (0.4%) followed by cheeses, RTE meat products and other RTE products (0.2% non-compliance each). For the batch-based sampling at retail the highest non-compliance was reported for soft and semi-soft cheese (2.8%), followed by products of meat origin other than fermented sausage (0.9%) and other RTE products (0.5%). Fig. 1 .4 shows that there is a slight decrease in incidence of L. monocytogenes in fishery from 2006 to 2007 and even sharper difference was found in 2008 in comparison with both the years (EFSA 2010).

Similar trends was observed in other sectors, except for hard and soft cheeses, where there was a strong raise of level of uncompliance. The presence of L. monocytogenes in soft and semi-soft cheese made from raw or low heat-treated cow's milk was detected in three out of seven qualitative investigations. For those investigations with positive findings, the proportions of positive samples ranged from 0.5% to 3.6%. Findings of levels above 100 cfu/g were not reported. Data on the presence of L. monocytogenes in cheeses made from sheep's or goat's milk were limited. 101 samples were investigated qualitatively, in which L.  monocytogenes was not detected. For soft and semi-soft cheeses made from pasteurised milk, a substantial amount of data were reported. A total of 4,265 samples of cheese made with milk from cows were analysed qualitatively and 1.6% were found to be contaminated with L. monocytogenes. The prevalence of the investigations ranged from 0% to 2.6%, the highest reported value was found by the Czech Republic from an investigation in which 2,423 samples were investigated. The Czech Republic also reported that 0.4% of 2,172 samples investigated quantitatively were found to contain L. monocytogenes in levels above 100 cfu/g (EFSA 2010).

Of 1,158 samples of soft and semi-soft cheeses made from pasteurized goat's and sheep's milk investigated qualitatively, and 55 investigated quantitatively, presence of L. monocytogenes was not reported. Hard cheese has been the subject of a number of reported investigations. The results for hard cheeses made from raw or low heat-treated milk are shown in Table LI5c and the result for hard cheese made from pasteurized milk is shown in Table LI5d. It appears that these cheeses may occasionally harbour L. monocytogenes, however very rarely in levels above 100 cfu/g. The Czech Republic reported findings of 1.7% contamination of 3,523 samples of hard cheese made from pasteurised cow's milk investigated qualitatively. Germany reported from investigations of hard cheese made from pasteurised cow's milk that 1.3% of 682 samples collected at processing plants, and 0.5% of 3,172 samples collected at retail were positive using the qualitative method, and further, that 0.2% of 1,621 samples collected at retail contained L. monocytogenes in levels above 100 cfu/g. It appears that the presence of L. monocytogenes in cheeses is quite seldom detected and numbers only rarely reach levels above 100 cfu/g. Nevertheless, the bacterium was isolated both from cheeses made from raw or low heat-treated milk and pasteurised milk as well as from soft/semi-soft cheeses and hard cheeses. In data for 2008, L. monocytogenes was most often detected in soft and semi-soft cheeses made from pasteurised milk (EFSA 2010).

A useful approach has been sampling at different steps during transformation process, where conventional analysis method were applied simultaneously with molecular protocols for species identification. From these investigations it was possible to identify most of involved sources: animals raw material have been proved as important source of food bacterial contaminants, even if it cannot be excluded contemporary influence of diverse other origins, like also food contact utensils as well as handling and processing locals. Generally animal Listeria isolates do not easily contaminate processing facilities due to predominant amount of better adapted competitors. Furthermore, apport from food processing equipment cannot be excluded, because most of reported food-associated listerial contaminations take place after heat treatment (EFSA 2010).

Fig. 1.4: Proportion of samples at retail in non-compliance with EU L. monocytogenes criteria, 2008 (EFSA 2010).

Tab. 1‑5: Compliance with L. monocytogenes criteria laid down by Regulation (EC) No 2073/2005 in food categories in the EU, 2008 (EFSA 2010)

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.