Listeria Monocytogenes free essay sample

The bacterium was named monocytogenes because one distinguish characteristic of infection in rabbits, which was the production of monocytosis in blood (Shuin et al. , 1982). L. monocytogenes is phychrophilic, has a temperature for growth of 0Â °C to 45Â °C (Barbosa et al. 1994), and enjoys a competitive advantage against other gram-positive and gram-negative microorganisms in cold environments, such as refrigerators. Recent investigations indicate that the organism can initiate growth at pH values as low as 4. 4. Also, it grows optimally at water activity of 0. 97. For the majority of strains, the minimum water activity needed for growth is 0. 93 (Lou et al. , 1999); however, some strains may be able to grow at water activity values as low as 0. 90 and survive for long periods of time at 0. 83 (Shahamat et al. , 1980). L. onocytogenes is able to grow in the presence of 10 to 12% sodium chloride; it grows to high populations in moderate salt concentrations (6. 5%). The bacterium survival in high-salt environments is significantly increased by lowering the temperature. We will write a custom essay sample on Listeria Monocytogenes or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Route of Exposure L. monocytogenes is particularly interesting as a foodborne pathogen in that it is ubiquitous in nature. The current understanding of human listeriosis epidemiology suggests that the organism is a common contaminant of food products. This contamination usually takes place on the surface of the products, with up to 15% harboring the organism. The presence of L. monocytogenes in the food processing chain is evidence by the widespread distribution of the listeriae in processed products. Occurrence of sporadic listeriosis appears to be more common in the spring and summer months. This could be explained by seasonal variations in the type of food products eaten by human populations, with higher-risk products eaten in the warmer months. Some outbreaks investigations suggest that certain ready-to-eat processed foods pose a high risk of contracting listeriosis for susceptible populations. These foods are usually preserved by refrigeration and offer an ppropriate environment for the multiplication of L. monocytogenes during manufacture, aging, transportation and storage. The entry of L. monocytogenes into food processing plants occurs through soil on clothing or equipments, contaminated hides or surfaces, and possibly healthy human carriers. The humidity and presence of nutrients support the growth of Listeria, which is commonly found in moist areas such as processing equipment, drains, etc (Cox et al. , 1989). In addition, Listeria can attach to different types of surfaces and biofilm formation has been observed in meat and dairy processing environment (Jeong et al. 1994). Post-processing contamination is the most likely route of contamination of processed foods. Currently, there is no evidence to indicate that L. monocytogenes can survive heat processing protocols. However, because it is a frequent contaminant of raw material used in food processing plants, there are plenty opportunities for reintroduction of listeriae into food processing facilities by cross contamination (Doyle, 1988). If the product is contaminated during its elaboration, the bacteria can survive and multiply throughout storage causing disease when it is consumed. In conclusion, epidemiologic investigations have repeatedly revealed that the consumption of contaminated food is the primary mode of transmission of listeriosis. Food has been identified as the vehicle of several major outbreaks of listeriosis investigated since 1981. Food Associated Some of the food products associated with L. monocytogenes include unpasteurized milk and products prepared from unpasteurized milk, soft cheeses, frankfurters, delicatessen meats and poultry products, and some seafood. Raw milk is a well-known source of L. monocytogenes. Pasteurization effectively inactivates this organism. However, fluid milk that is contaminated after pasteurization and stored under refrigeration may achieve very high populations of L. monocytogenes after one week; Furthermore, temperature abuse may enhance the multiplication of bacterial cells. L. monocytogenes can also be found in cheese because of its relative hardiness to temperature fluctuations, ability to multiply at refrigeration temperature and salt tolerance. During manufacturing process, L. monocytogenes is primarily concentrate in the cheese curd, with only a very small portion of cells appearing in the whey. Then, during ripening of the cheese, the numbers of cells may increase (Camembert), decrease gradually (Colby or cheddar), or decrease rapidly (blue cheese) and then stabilize. In addition, cooked and ready-to-eat meat and poultry products have been implicated as the source of sporadic and epidemic listeriosis on several occasions in North America and Europe (Schwartz et al. , 1989). L. monocytogenes attaches strongly to the surface of raw meats and is difficult to remove or inactivate. The multiplication in meat and poultry depends on the type of meat, pH, and the type of cell populations of competitive flora (Farber et al. 1999). However, it has been shown that poultry supports the growth of L. monocytogenes better than other meats. Furthermore, the incidence of L. monocytogenes in ready-to-eat products has become a major concern for the meat processing industry. Ready-to-eat meat products that have been received a heat treatment followed by cooling in brine before packaging may provide a particularly conducive environment for multiplication of L. monocytogenes because of the reduction in competitive flora and the high salt tolerance of the organism. L. onocytogenes has also been isolated from domestic and imported, fresh, frozen, and processed seafood products, including crustaceans, molluscan shellfish and finfish (Jinneman et al. , 1999). However, seafood consumption is still much less when with consumption of meats and cheeses. Also, the production of seafood products is done on a much smaller scale than meat and cheese manufacture. This may be the reason that large outbreaks have not been reported and that case-control studies have not identified this group as a major risk of listeriosis (Rocourt et al. 2000) Characteristics of the disease Human disease usually occurs in high risk groups, who have a predisposing disease that leads to impairment of their T-cell mediated immunity. However, may occasionally occur in individuals with no predisposing conditions. Some of the high risk groups may include pregnant woman, neonates, and immunocompromised adults (Goulet et al. , 1996). On average, there are 0. 7 cases of listeriosis per 100,000 people, but the disease is seen three times higher in the elderly (gt;70) and 17 times higher in pregnant women. A wide variety of clinical syndromes have been associated with L. monocytogenes in both humans and animals. In healthy individuals, the disease can take the form of mild to substantial flu-like symptoms, including: fever, fatigue, nausea, cramps, vomiting and diarrhea. More severe complications can include: encephalitis, septicemia, mononucleosis-like syndrome, pneumonia, endocarditis, aortic aneurysm, hepatitis, urethritis, rhombencephalitis, peritonitis, liver abscess, febrile gastroenteritis, CAPD peritonitis, septic arthritis, etc. (Dalton et al. , 1997). Lonocytogenes in pregnant women can lead to an intrauterine infection, resulting in stillbirths and miscarriages. Newborns can develop meningitis after birth via transplacental transmission. The onset time for serious complications of listeriosis can be anywhere from a couple of days to three weeks. Mortality of untreated infections is among the highest of all foodborne illnesses, 70 percent. The infective dose of L. monocytogenes is not yet known, it is related to variables, including: strain, susceptibility of the victim, type food from which is was consumed, etc. Mode of Action Listeria monocytogenes is the most invasive bacteria known. The principal site of infection is the liver, but it can invade many cell lines of different types (microphages, fibroblast, hepatocytes and epithelial cells). Listeria monocytogenes infects the host via oral route. Once the bacteria are ingested, they reach the intestine and are translocated between enterocytes and M cells (Pron et al. , 1998); however, the intestinal dendritic cells in the Peyer’s patches appear to be the preferred site for invasion and multiplication (Kolb-Maurer et al. 2000). Bacteria are then internalized by resident macrophages, in which they can survive and replicate. They are subsequently transported via the blood to regional lymph nodes. When they reach the liver and the spleen, most listeriae are rapidly killed. Depending on the level of T-cell response induced in the first days following initial infection, further dissemination via the blood to the brain or, in the pregnant individuals, the placenta may subsequently occur. In addition, bacteria are internalized in membrane-bound vacuoles, which are lysed within 30 minutes. Intracellular bacteria are released to the cytosol and begin to multiply with doubling time of about one hour. These intracytoplasmic bacteria become progressively covered by a cloud of cell actin filaments that later rearrange into a polarized comet tail up to 40 ? m in length (Crossart, 1995). The actin comet tail is made of actin microfilaments that are continuously assembled in the vicinity of the bacterium, then realeased and cross-linked. The entire bacteria cycle is completed in about 5 hours. If cytochalasin D is added after entry, bacteria do not spread within the cytosol. They replicate and form microcolonies in the vicinity of the nucleus. Hence, actin polymerization is essential to intracellular movement and cell-to-cell spreading. In summary, the pathogenic mechanism of L. monocytogenes involves the following steps: adhesion to the host cells, lysis of the phagosome, replication in the host cytoplasm, actin-based intracellular movement and propulsion, and the intercellular spread. Biotransformation Listeria monocytogenes is of interest to a board range of investigators, including food microbiologist, clinicians, immunologist, medical microbiologist, and even cell biologist because it is developing resistance to most currently used antibiotics. In the past, individuals who develop listeriosis have usually been treated with penicillin or ampicillin in conjunction with an aminoglycoside (Charpentier et al. , 1999), although tetracycline, erythromycin or chloramphenicol, alone or in combination, has also been used (Hof et al. , 1991). More recently, reports of resistance in Listeria spp. have been published. Such increases in antibiotic resistance have been linked to over-use of antibiotics in animals and humans (Rao, 1998) since these therapeutic compounds were identified nearly 60 years ago. This resistance may arise from a mutation in an intrinsic chromosomal gene, or by acquisition of exogenous genetic material carrying single or multiple resistance determinants (Levy, 1994). It is now clear that such transfer is possible between unrelated bacterial species (Kruse et al. 1994), and that these interactions are a frequent and important means of genetic exchanges among microorganisms. In conclusion, it is evident that antibiotic resistance is becoming more and more widely reported in all bacteria. Control and Prevention Because L. monocytogenes can grow at refrigerator temperatures, the Center of Disease Control and Prevention (CDC) advise all consumers to reduce the risk of illness by using a refrigerator thermometer to make sure that the refrigerator always stays at 40 Â °F or below and using perishable items that are precooked or ready-to-eat as soon as possible (CDC, 2005). For high risk groups it is recommended to not consume hot dogs and luncheon meats, unless they are reheated until steaming hot; not eat soft cheese such as Feta, Brie, and Camembert cheeses, unless it is labeled as made with pasteurized milk; not eat refrigerated smoked seafood, unless it is contained in a cooked dish; and not drink raw (unpasteurized) milk or eat foods that contain unpasteurized milk. Therapy When listeriosis is a likely diagnosis, the use of ampicillin or, in penicillin-allergic patients, vancomycin will provide empiric coverage for L. onocytogenes until the diagnosis is made by culture. Once listeriosis is confirmed, a combination of ampicillin and gentamicin is the current therapy of choice for all forms of listeriosis. The duration of the treatment for invasive listeriosis has not been studied. Relapses appear to be uncommon, and two to three weeks of therapy with ampicillin and gentamicin is sufficient for most forms of listeriosis. Rhombencephalitis with abscess formation in the central nervous system may require more prolonged therapy, but data are not available that support treatment beyond four weeks (Lorber, 1997).

THE BERMUDA TRIANGLE essays

THE BERMUDA TRIANGLE essays The Bermuda Triangle, located between Florida, Puerto Rico, and Bermuda, has had many mysterious events occur over the past five hundred years. There are many facts people can learn from this place. Christopher Columbus was the first known discoverer of the Bermuda Triangle. Many United States planes and ships, as well as the many airlines planes and cruise boats that have been lost, never to be seen again. In the area between Florida, Puerto Rico, and Bermuda, there have been many strange disappearances. Many ships and planes have been disappearing in this area of the Atlantic Ocean. The Bermuda Triangle started being noticed in 1904, when many people became missing. Since 1945, more than one hundred planes and ships have vanished, and more than one thousand lives have been lost in the last twenty-six years (Berlitz 11). The amazing part of this is that many searches have been conducted to find survivors or any wreckage from these boats and planes and nothing has ever been found. Some of the many planes have disappeared during normal flying and while still in contact with their base. The base says the radio just faded out. Many of the disappearances have occurred during or near Christmas. Experts have not yet discovered why the Bermuda Triangle is especially anonymous during this time (Kische 7). After plotting these disappearances on a map, you will find that it has been forming a t riangle or a kite shape. This is why they call it, The Bermuda Triangle. They have made the name, "The Port of Missing Ships," to the place that ships go after they have disappeared. Until this day, many strange disappearances have occurred in this area. Christopher Columbus was the first known observer of this area. It is believed that he discovered this area while on route to what is now known as America. In 1492, Columbus recorded that he and his crew observed a large ball of fire falling from the sky into the sea. He also recorded that his co...

Newspaper Industry Essay Example | Topics and Well Written Essays - 2000 words

Newspaper Industry - Essay Example We shall tackle both sides of the argument individually so as to gain proper insight on the issues involved in the debate. The negative impact that the internet has had on the newspaper industry is mainly as a result of the switch of consumers from printed material to electronic material for news, entertainment among other uses. The impact of this switch is evident in the steady decline of readership and circulation which has since become more of a norm than an exception, with readerships dropping in rates as high as 16% (Miller, 2005) The internet affects print media on three major frontiers, advertisement revenue, readership and innovation and technology. Since the largest source of revenue for newspapers is advertisement, newspapers stand to suffer if they do not offer competitive packages for their customers. This has led to severe rates undercutting which has in turn dug into the revenues of the newspapers resulting in job cuts, plagiarism and writing of untrue and fictitious stories and events with shameless abandon (Hughes, 2006). The reason for this can partially be attributed to the fact that a dvertisers try to promote their products to the highest possible audience at the lowest cost, the internet offers a better than perfect substitute for newspapers for several reasons. For instance, the internet has far much more ahead as far as accessibility is concerned compared to newspapers. Whereas the latter offers some options for leisure and recreation in one or two pages, these options are comparatively limited to those which the internet can offer because at the simple click of a button one can access millions of online entertainment sites. Online advertisements are also more effective because in the first place, there are lesser limits to the size of the advertisement in relation to the total surface area available wherein it might take up to a quarter of the page at a minimal cost. In contrast, a quarter page advertisement in a newspaper is bound to cost quite a lot, actually about 21times that of the online advertisement (Karp, 2007). It is therefore quite clear that onli ne advertisements are more cost effective than their print counterparts. In addition, online advertisements have the option of containing hyperlinks, which connect the user to the advertiser's website where he can find much more information about them, their products and/or services, giving rise to more opportunities of turning the advertisement leads into sales. The newspaper advertisements can do little else than just display the advertisers' contact details after the main content. The advertisements themselves have much better design when online because they may be made dynamic, which basically means that they may have movements and even sounds to accompany them which greatly enhances their memorability and ability to capture the attention of the target reader. In sharp contrast, advertisements in newspapers are limited to showing a single picture which may not be as attractive. The

English writing Essay Example | Topics and Well Written Essays - 250 words

English writing - Essay Example Based on the poor treatment that Catherine receives from her husband, she opts to use her beauty and wits to her advantage and also finds lovers for herself. Her plot is that of seizing power once the ruler of the time, Empress Elizabeth dies and Catherine forms secret alliances in preparation for this. At first opportunity, Catherine succeeds in taking the crown and she takes charge of the kingdom as he rules instead of her husband. Her quest is that of conquering more territories as a way of expanding the Russian kingdom, which was one of the visions that Empress Elizabeth had sought to achieve. Catherine faces the challenges of war and conspiracies that seek to undermine her role, but she manoeuvres by using all the power she has in order for her rule and control to survive. All this comes at a cost as she has to contend with being unhappy, which is the cost of being at the helm of a significant kingdom. Her past is overshadowed as she started as a pawn and rises to become the wife of the Duke and the Empress of the Russian kingdom making her to be more powerful. Her kingdom becomes modernized through her efforts and wits in which it grows to be an expansive and civilized one (Moss 267). In the end, the film title explains how Czar ended up becoming Catherine the Great as portrayed in the

Alternative methodology Essay Example | Topics and Well Written Essays - 500 words

Alternative methodology - Essay Example Scientific theory is usually objective, while the constructivist approach is mostly subjective. This paper aims to identify the ways in which the study would have been different if the researchers had taken the scientific theory or positivist approach as opposed to the constructivist approach used. This difference will be identified by focusing on the epistemology, ontology, methodology and the effects of the theory on the data generated and inferences used. According to Gialdino (2009), epistemology is the approach that the researcher takes to the study based on the theory being used. As already identified, scientific theory usually takes on the objective construct, while constructivist paradigms usually involve subjectivity. The objectivity or subjectivity of the researcher is the epistemology of the research. In the case of Swain and Hammond (2011), it is evident that the research took a subjective view, which means that the researchers used the constructivist approach. In this case, if the researchers had taken the scientific approach, the research would have been different. In the scientific approach, the researchers remain objective and try to eliminate bias from the research. The ontology of research is a concept that deals with the relationships between different aspects of the society, and is different in both scientific and constructionist approaches (Hein, 1991). In the constructionist approach, researchers consider that there is no true knowledge, that knowledge is interpreted differently by different individuals. Since the constructionist approach is usually qualitative, it differs from scientific research in its ontology. If the research by Swain and Hammond (2011) had taken a scientific approach, the ontology would have been differentiated. Scientific or positivist paradigms use knowledge as the goal of

Comparison of The Marriage of Heaven and Hell and The Songs of Innocenc

Blake’s â€Å"The Songs of Innocence & Experience† and â€Å"The Marriage of Heaven and Hell† play an important role in the age of romanticism and important step in romantic poetry. Looking at the two pieces as a comparison, it can be seen that Blake used two different pieces to question traditional institutions. Blake questions institutionalized religion with â€Å"The Marriage of Heaven and Hell† and questions the industrialized age with â€Å"The Songs of Innocence and Experience†. â€Å"The Marriage of Heaven and Hell†, questions the very fabric of traditional religion through Blake’s criticisms on the need for change towards political and religious freedoms. Blake attacks the ways in which society has become by comparing good and evil while challenging the orthodoxy of conventional religion. Blake explains that people are resisting their desires and in doing so confining to the rules that the convention of religion has placed on t heir followers. â€Å"The Songs of Innocence & Experience comments on the industrial revolution and the affects it’s had on society. Blake touches on the socials evils that come with the industrialized revolution and the consequences of an unequal social structure. Blake comments on how the corruption of society hinders the freedoms people once felt as children bringing to light such social problems as urban poverty and misery. Blake identifies the industrialization revolution and conventional religion as the problem between man and the return to the natural state of being. Blake insinuates that the world has lost its freedom and natural beauty from being consumed in a material world full of corruption and misery. Blake uses radical questioning to address the issues of conventional religion and industrialization through â€Å"The Song... ... through both of his pieces that conventional religion has condemned people to confinement and that as long as there is oppression of desire no individual can truly be free. Works Cited Blake, William. â€Å"The Marriage of Heaven and Hell†. The Broadview Anthology of British Literature: The Age of Romanticism.V.4 2006 44-51 Blake, William. â€Å"The Songs of Innocence and Experience†. The Broadview Anthology of British Literature: The Age of Romanticism.V.4 2006 36-44 Musante, R.. â€Å"Embracing the divine: The life of spirit in William Blake's "Songs of Innocence", "Songs of Experience", and "The Marriage of Heaven and Hell". Diss. Middle Tennessee State University, 2007. Dissertations & Theses: A&I, ProQuest. Web. 26 Nov. 2010. Swearingen, James E. â€Å"William Blake’s Figural Politics†. ELH. Vol 59, No 1 (Spring 1992). John Hopkins University Press.

Barefoot running

Athletics is one of the major sports in the world with running being the key event. The major debate relating to running concerns the benefits of running barefoot over running in shoes. Hersher (2010) argues that there is a growing trend of athletes going shoeless and taking on the lifestyle of running barefoot. Quite a number of well known international athletes have effectively completed barefoot. Barefoot running in long distance events is clearly not a hindrance to performance (Montgomery, 2010).Numerous studies have been conducted to determine the most appropriate mode of dressing during running; this includes running in shoes and barefoot running. Proponents of barefoot running, as indicated by Montgomery (2010), argue that it enhances foot biomechanics and also reduces risk to injury. My concern on the issue of barefoot running increased after realizing that quite a number of runners complete in bare feet during major events. This review is aimed at showing that running barefo ot increases performance and reduces the risk of injury.Benefits of barefoot running Studies, according to Barkoviak (2010), have revealed that people who run barefoot greatly avoid heel-striking and instead land on the mid section of the foot. As a result these runners utilize the architecture of the foot and leg in addition to some physics devised by Isaac Newton to prevent damaging and potentially hurtful effects, which are two to three times equal the body weight, that shod heel-strikers repeatedly undergo through (Warburton, 2001).Barefoot runners are at an advantage as compared to those who run in shoes, because they subject their feet to minimal damage due to the fact that they hold their feet differently (Hersher, 2010). They land on the midsection or the front of their foot thereby greatly reducing impact collision. People who run in shoes, on the other hand, generate a very high collision impact when they heel-strike. Barefoot runners tend to land with a bouncy step toward the front of the foot.Barefoot runners also tend to stretch out their toes more at landing; this helps them avoid collision by reducing the effective weight of the foot that suddenly comes to a stop after landing and through a springy leg (McDougall, 2010). A lot of people think that barefoot running is dangerous and hurtful, but in reality an individual can run on the worlds hardest and roughest surfaces without experiencing any discomfort or pain. However heel-striking is painful when running barefoot (McDougall, 2010).This is because it causes a great collisional force every time a foot lands on the ground. Modern running shoes are designed in such a way as to make heel-striking comfortable and easy. The padded heels, of modern shoes, reduce the force of impact and as a result make heel-striking less punishing. However, people who run in shoes only use a small percentage of their leg muscles. On the contrary, barefoot runners use different muscles of their legs (Warburton, 2001) . As a result the strength of their calf and foot muscles is developed rapidly (Warburton, 2001).Studies, as Barkoviak (2010) asserts, have revealed that damage to the foot muscles is higher in people who run in shoes as compared to those who run barefoot. It has been discovered that chronic damage to bone and connective tissue in the legs are uncommon in developing countries, where people usually run barefoot, as compared to developed countries, where it is rare to find a person running barefoot (McDougall, 2010). Running shoes tends to aggravate the risk of plantar fasciitis in addition to other chronic damage of the lower limb through adjusting the transfer of shock to muscles as well as other supporting structures (Montgomery, 2010).Montgomery (2010) argues that running in shoes makes the small muscles in the legs to weaken, and the connective tissue and natural arches to stop functioning properly. Shoes insert orthotics as well as extra padding, which results in poor foot biome chanics and increase in the risk of damage to the foot, leg, and the knees (Hersher, 2010). Muscles, tendons, and ligaments of barefoot runners are stronger as compared to those who run in shoes. This strength helps them develop a more natural gait thereby improving the balance of athletes along with helping them stay connected with their environment.Barefoot running is also economically beneficial, in regards to the energy cost of running, as compared to running in shoes. Research, according to Barkoviak (2010), has shown that increasing the amount of mass on the feet increases the rate of oxygen consumption. Running barefoot is as Warburton (2001) argues, beneficial as it reduces the rate of oxygen consumption thereby enabling athletes to compete effectively. However, as a disadvantage, it is impossible to run barefoot in some weather conditions due to minimal foot protection. Running shoes are very beneficial in extreme weather conditions as they play a protective role.Conclusion Barefoot running is more beneficial a compared to running in shoes. There is a growing trend of athletes going shoeless and taking on the lifestyle of running barefoot. Proponents of barefoot running argue that it enhances foot biomechanics and also reduces risk to injury. People who run barefoot greatly avoid heel-striking and utilize the whole architecture of the foot and leg thereby enhancing the development of their foot muscles, ligaments and tendons. Damage to bone and connective tissue in the legs is less common in people who run barefoot.Muscles, tendons, and ligaments of barefoot runners are stronger as compared to those who run in shoes. Running barefoot is beneficial as it reduces the rate of oxygen consumption thereby enabling athletes to compete effectively. Reference: Barkoviak M. , (2010), Study: Running Barefoot Better Than Wearing Running Shoes, Retrieved on May 1, 2010 from http://www. dailytech. com/Study+Running+Barefoot+ Better+Than+Wearing+Running+Shoes/articl e17535. htm Hersher R. , (2010), Barefoot running easier on feet than running shoes: New research castsdoubts on some major assumptions, retrieved on May 1, 2010 from http://harvardscience. harvard. edu/foundations/articles/barefoot-running-easier-feet-running-shoes McDougall C. , (2010), Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never, ISBN 0307279189: Vintage Books Montgomery B. , (2010), Barefoot Running: Should You Ditch Your Running Shoes and Bare it All? Retrieved on May 1, 2010 from http://walking-runningtraining. suite101. com/article .cfm/barefoot-running Warburton M. , (2001), Barefoot Running, retrieved on May 1, 2010 from http://www. sportsci .org/jour/0103/mw. htm