Foodborne Gastroenterities Of Salmonella And Shigellas Biology Essay


The Salmonella bacteria cause Salmonellosis, which usually, after one to three days of infectivity, cause abdominal spasms, diarrhoea. In most cases it does not require medical action, but in some cases because of the intensity of the symptoms, the patients would need to undergo treatment with antibiotics, this is usually the case for people with weak immunity systems. It is rod shaped and is a gram negative bacterium. The disease has been taking place since more than 100 years. And its nomenclature was from the name of its discoverer. (CDC, 2009)

The Shigella bacterium causes Shigellosis; it has the same symptoms and incubation period as the Salmonellosis. It takes up to one week to resolve, usually without hospitalisation, unless it hits infants of elderly. It is a non spore forming rod shaped gamma negative bacterium that was discovered a century ago by a Japanese scientist. There are different types of Shigella, we have the Group D that is the most common, and the group B Shigella and the deadliest one, the type one Shigella that usually hits in the developing countries. (CDC, 2009)

How common are Salmonellosis and shigellosis?

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Since Salmonellosis doesn't usually require treatment, the number of cases reported, 40000 cases in the United States, is therefore less that number of people that have the disease, it is more frequent in summer. It is five times more likely for a child under the age of five to get diagnosed with the illness, it is caused by the fact that they have a weak immune system. Around 400 people die from Salmonellosis every year. (CDC, 2009)

The same goes for the reported cases of shigellosis, around 14000 cases are reported where many more are not. It is usually found where there is bad hygiene; it is also more common in summer times. Infants are the most likely to get shigellosis. It is usually spread amongst children and then to their families. It is a very illness in developing countries. (CDC, 2009)



Salmonellosis varies with the type, the dose the strain and the carriers status. Some are very deadly, and some rare ones have unknown pathogenicity. Depending on the type of salmonella, the dose required to cause typhoid varies. The microorganism enters the intestines and pierces the mucosa, and is blocked in the mesenteric lymph nodes where they multiply and start the disintegration. Some bacteria and endotoxins make their way to the blood stream. (Todar, 2008)

Even after being cured from Salmonellosis, some patients will still have salmonella excretion, and this would make them carriers of the disease for a long period of time. The usage of antibiotics would stop this excretion by patients. With bad processing of sewage water, salmonella would survive to reach the sewage plant and then the rivers where the living organisms, which are later eaten by humans, become carriers of the bacteria. (Todar, 2008)

Only humans are capable of getting typhoid. With the development of good hygiene practices and good management of water and food, the rate of contamination with salmonella decreases, and therefore there would be a decrease of typhoid. (Todar, 2008)

Foodborne infections from salmonella usually take half a day to show their symptoms, if the amount of salmonella found in the food is sufficient. Most of the times, the infections are cured spontaneously after two to five days. (Todar, 2008)

Salmonella caught by humans could be the result of either animal Salmonellosis or, the most common one, from the infection of the muscles with the manure while disembowelling the animals, or by the management of the cadavers. It the infection was only on the surface of the meat, good cooking could remove all trace of contamination, but the handler should be cooking with good hygiene manners. On the other hand, if the contamination was not on the surface the multiplication of the bacteria to a certain amount could cause an infection; foods that support this multiplication are usually mayonnaise and eggs. Regarding fruits and vegetables, they could carry salmonella if they were washed with bad water or they could get contaminated from fertilizers. (Todar, 2008)

Because most of the food consumed in developed countries are not prepared at home, but rather commercially prepared, the incidence rate of infections is very high when comparing them to developing countries. (Todar, 2008)

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Salmonella Enteritidis Infection

One other significant public health difficulty in several European countries and the U.S is Egg-associated Salmonellosis, this Salmonella Enteritidis could be contained by completely regular- appearing eggs, and this bacterium could lead to a serious illness if the eggs are undercooked or eaten raw without cooking. Throughout the 1980s, this type of egg-related illness was widely common in the north-eastern United States, however currently the occurrence of this illness caused by Salmonella Enteritidis originating from contaminated eggs is growing in different regions of the United States. (Todar, 2008)

Conversely, distinct from the eggborne Salmonellosis that was present in the last decades, the existing Salmonella outbreak is caused by disinfected and undamaged grade "A" eggs and the basis behind this is that Salmonella Enteritidis works on the ovaries of hens by silently infecting them, which causes egg contamination prior to the formation of shells. The majority of Salmonella types reside inside the intestinal tracts of birds and animals, and they're passed on to humans through the ingestion of infected foods from animal origin. In the 1970, strict measures were implemented for the cleaning and inspection of eggs, which lead to tremendously reducing the number of cases of Salmonellosis originating from the exterior egg shells fecal contamination. (Todar, 2008)

Are there long term consequences to a Salmonella infection?

The symptoms that usually accompany the infection with the Salmonella Enteritidis are mainly fever, diarrhea, and abdominal cramps starting to appear 12 hours to 3 days following the consumption of Salmonella infected food or drink. Whereas, the disease generally progresses for a period of 4 to 7 days, and commonly patients' condition improve with no need of antibiotic treatment, the diarrhea resulting from this disease can be severe, and for the person to recover completely he may need hospitalization.  Infants, the elderly, and people having damaged immune systems such as HIV patients, may possibly experience higher severity of this illness, where the scattering of the infection might take place from the intestines through the bloodstream, subsequently to other different organs in their body, which may be fatal for the patient if not treated rapidly by using antibiotics. Other symptoms of Salmonella infection occurring with a minority of people, is the development of joint pain, eye irritation, and painful urination. These symptoms specify a syndrome called Reiter's syndrome, which could progress from several months to years, leading to difficultly treated chronic arthritis. (Todar, 2008)

Transmission of Shigella

The route of transmission of Shigella from people infected with this disease is the fecal-oral route, where the presence of Shigella is high in the diarrheal stools of those people during their illness period, and after that with one or two weeks. The Most common incidence of Shigella contamination results from the transmission of the bacteria from the soiled fingers or stools of the infected person orally to the mouth of a second person. Such transmission occurs due to inadequate practice of basic hygiene and insufficient hand washing. This is predominantly expected to take place amongst incompletely toilet-trained toddlers, where the playmates and family members of those children are more likely to develop an infection. Hygienic practices, such as careful and repeated hand washing by soap, exercised by all age groups could be helpful in stopping the spread of Shigella from an infected person to other people. (Todar, 2008)

The efficiency of the Shigella transmission is high; since the illness could be triggered by very minute doses of the bacteria (10 to 200 organisms). Consequently, if proper hygienic conditions are not applied, Shigella could easily multiply through the fecal oral route. (Todar, 2008)

Epidemics resulting from outbreaks of Shigella could be either foodborne or waterborne. Becoming infected with Shigella could be obtained from the ingestion of food contaminated by ill food handlers. Also, contamination of vegetables with Shigella can be a result of using wastewater in field to irrigate crops, or harvesting in where infected field workers defecate. The transmission of Shigella could also occur through flies reproducing in feces, where flies can pollute food later. Water might be contaminated with Shigella if it contains wastewater or a person with shigellosis bathes or swims in it; however the infection could be transmitted through swimming or drinking in this water. (Todar, 2008)

The Shiga Toxin

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The E coli 0157:H7 and the Shigella dysenteriae produce the shiga toxin. The symptoms and the causative organism are the base of the nomenclature of the syndromes linked with shigellosis, such as stomach pain, unsettled stomach and diarrhoea. Depending on the dose of infection, the symptoms usually appear after a couple of hours. No cure is available, it is essential to keep a high level of fluids in the body, and maintain the kidney's utility. The toxin could, after being ingested food, affect the functionality of the lungs. (Todar, 2008)

Pathogenesis of Shigella flexneri

Shigella flexneri is a major reason for bacillary dysentery. Symptoms rising from the infection contain abdominal pain, fever, diarrhea, as well as vomiting and blood in stool. Transmission includes fecal-oral route, as well as contaminated water and food. After ingestion, bacteria build up its way to the large intestine. Once found in large intestine, bacteria enter the epithelial cells of the intestinal mucosa. Following the entrance, intracellular multiplication takes place and extends to adjacent epithelial cells, leading to tissue damage. (Todar, 2008)

Evolution of the Shigella virulence plasmid

Current genetic analyses advocate that Shigella do not constitute a different type, but they are within the E.coli species. The Following done analyses proved indicate that three main Shigella clusters are said to have evolved 35,000 to 270,000 years ago, which accompanies agricultural development, thus making shigellosis an early human infectious disease. (Todar, 2008)


Vaccination against Typhoid Fever: In United States, three vaccines are found to combat typhoid fever: Oral live-attenuated vaccine, parenteral heat-phenol-inactivated vaccine, and a newly licensed capsular polysaccharide vaccine for parenteral use. A fourth vaccine, an acetone-inactivated parenteral vaccine, is presently available only to the armed forces. (Todar, 2008)

Live oral vaccines: oral vaccines are with no efficacy, vaccines using living a virulent bacterium have revealed promise. Live Oral Vaccine must not be given to children of ages ranging from 1 to 5.It's given in four doses, two days apart, as intended for protection. 

The parenteral heat-phenol-inactivated vaccine has been widely used for many years. In field trials involving the vaccine, efficacy over the 2- to 3-year periods ranged from 51% to 77%. The inactivated Typhoid Vaccine should not be given to children younger than 2 years of age. Only One dose provides protection.

The newly licensed parenteral vaccine [Vi capsular polysaccharide (ViCPS)] is composed of purified Vi ("virulence") antigen, a capsular polysaccharide elaborated by S.Typhi and secluded from blood cultures.

Treating Shigellosis is generally done by antibiotics. Furthermore, suitable actions eliminate the bacteria found in gastrointestinal tract and diminish the illness or infection time. Due to unsuitable and inappropriate antibiotics use, various Shigella types are becoming more and more resistant. Several Anti diarrheal agents such as, Imodium, or Lomotil should be definitely avoided since they are expected to make the illness worse. (Todar, 2008)


What can a person do to prevent Shigella?

Presently, preventing shigellosis is impossible. Likewise, basic essential measure could help treating the spreading Shigella from a contaminated person to another. The First is regular and cautious hand washing with soap. Infected people shouldn't prepare food for others. Secondly, improving worker hygiene throughout handling and packing can help prevent contaminated produce. (CDC, 2009)

What can a person do to prevent Salmonella?

Currently, no vaccine for Salmonellosis is found. People should not eat raw foods, such as meat, eggs, or even dairy products, since it may be contaminated by Salmonella. In addition, meat and poultry should be well- done and cooked till the pink color disappears. Cross contamination is important and highly promotes the separation of raw and well-cooked and ready foods. As well as, all kitchen equipments and utensils should be disinfected by careful washing. (CDC, 2009)

People with Salmonellosis are prohibited to prepare foods. Furthermore, people must always wash their hands after animal contact. A child can be easily exposed to the bacteria simply from holding, hugging, and cuddling an animal. Improving hygiene is a very effective preventative in agricultural sectors. Moreover, presenting proper education is proven to be helpful. (CDC, 2009)

Case Studies


Salmonellosis outbreak in The United States 2008

In the spring of 2008, a Salmonellosis outbreak was recorded in the United States, when hundreds of people where diagnosed with salmonella infection after the consumption of contaminated food products. The CDC and Food and Drug administration in the U.S conducted an investigation to predict that these food products constitute possibly of raw tomatoes, Serrano peppers, and fresh jalapeño imported from Mexican farms. (CDC, 2008)The cases started to appear from April 2008, for a period of more than three months, reporting the biggest nationwide Salmonellosis outbreak since 1985. The CDC documented that: "The rare Saint Paul serotype of Salmonella enteric caused at least 1329 cases of Salmonellosis food poisoning in 43 states throughout the United States". (CDC, 2008) Not less than 257hospitalizations were considered to be associated with the outbreak, causing one death as a minimum. The CDC states that "it is likely many more illnesses have occurred than those reported, estimated 52,826 illnesses from this outbreak, and 173 estimated cases per million throughout the United States". (CDC, 2008)

Variety of Contaminated Food

The FDA and the CDC carried out an investigation that proved that Salmonella is, in fact, transmitted through the consumption of raw or cooked tomatoes as 80 percent of affected people, who took part in the study, will agree to. However, 68 percent of people examined under this study attested that the consumption of either raw or cooked tomatoes did not have any effect. The study went on to show that possible sources of contamination included various tomato (or a different crop) harvested from multiple regions caused cross-contamination along the distribution chain at the packaging stage after being collected simultaneously or other tomato crops from a single region that may have been infected with Salmonella by environmental agents that may include water supply. "According to Dr. Douglas Powell, Director of the International Food Safety Network, possible suspects aside from tomatoes include salsa, jalapeño peppers, green onions, and cilantro." (CDC, 2008)

Source of the contamination

As a reaction towards the ongoing development of disease at different onset dates, the Center for Disease Control expected that in a certain period after beginning of the outbreak, the farm that is planting contaminated crops shifted its crops production from tomato to jalapeño, since jalapeño peppers, mainly harvested from the areas along Texas, New Mexico and Mexico, were also highly suspected by the Food And Drug Administration to be an infection source, leading to a cross-contamination among the different crops. Remarkably, the FDA affirms that "there's no clear indication that there's any obvious crossover point" (CDC, 2008) where tomatoes from both Florida and Mexico could have been contaminated at the same place. (CDC, 2008)


Subway Restaurant Shigella Outbreak

A Subway restaurant in Lombard, Illinois, close to Chicago, was a source of Shigella outbreak that affected no less than 116 people who were diagnosed with symptoms associated with severe Shigellosis; symptoms comprised of diarrhea, fever, and abdominal cramps, which were found on 7 people hospitalized with Shigellosis. The Chicago county health officials were working to restrain the spread of the outbreak by shutting down the restaurant.  Costumers of the restaurant getting tested and realizing that their infection is not a normal stomach ache increased the number of confirmed ill cases with Shigellosis.  The Illinois health department recommended that "anyone who ate at the Lombard Subway restaurant between February 24 and March 5 and experiencing any gastro-intestinal illness get tested". (Clark, 2005)



Salmonella and Shigella can both be deadly depending on doses taken, however can be easily cured in most cases. Even though many scientific trials proven to be successful, no vaccines have been found. Bacteria can be easily transmitted through either food or water. Shigella and Salmonella cause diarrhea as well as fever and abdominal pain. Many preventative measures can be done in order to hinder or stop the transmission of the infectious disease into your body, such as improving hygiene, packaging, and handling through hand washing and consuming well-cooked meals.