Salmonellosis Spring '14

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Salmonellosis is the name of the infection caused by bacteria of the genus Salmonella. It is one of the most common food-borne illnesses reported in the United States. Salmonellae are rod-shaped, motile, Gram negative bacteria that possess an endotoxin and are known to cause disease in animals and birds, in addition to humans. [9,10,11,13] Transmission typically occurs through the ingestion of food contaminated with fecal matter. [10] This may occur by handling pets, raw or undercooked meat, and various other modes of transmission. While the majority of those infected recover fully within several days, others may face severe complications. [10] This is because certain strains can cause typhoid fever, as well as the less severe paratyphoid fever. [10] If necessary, (whether typhoidal or nontyphoidal), numerous antibiotics can be effective in combating Salmonellosis. [10] However, growing resistance of certain Salmonella strains is limiting the efficacy and success rate of this treatment. [10,11] Prevention of nontyphoidal infections requires diligent sanitary practice and proper hygiene because currently there is not a viable vaccine for human use. Typhoidal infections may be prevented by an effective vaccination.

Fig. 1 Micrograph of Salmonella bongori
Fig. 2 Gram stain of Salmonella typhi

Contents

Disease Name

Salmonellosis


Organism

Salmonella bacteria: S. bongori and S. enterica [11,14]

Most Common Serotypes (strains):

Salmonella Enteritidis - most common strain; prevalent in poultry [14]

Salmonella Typhimurium - second most common; prevalent in beef and known to be antibiotic resistant [14]

Salmonella Newport - typically associated with turkey products [14]

Salmonella Javiana - responsible for numerous exposures from reptiles and amphibians [5,14]

Salmonella Heidelberg - second most reported strain; again seen mainly in poultry, but specifically in eggs [14]


Scientific Nomenclature and Classification

Scientific Classification Kingdom: Bacteria Phylum: Proteobacteria Class: Gammaproteobacteria Order: Enterobacteriales Family: Enterobacteriaceae Genus: Salmonella Species: S. bongori or S. enterica

The genus Salmonella belongs to the same family of bacteria as Escherichia coli. There are two known species of Salmonella: S. bongori and S. enterica. But of the two species, there are 6 known subspecies: enterica (I), salamae (II), arizonae (IIIa), diarizonae (IIIb), houtenae (IV), and indica (VI). [10,13] Further classification gives rise to over 2500 serotypes. [10,13] Great debate has been stirred over the proper manner in which to distinguish the different serotypes. For example Salmonella serotype Typhi is acceptable in some scientific circles, while others prefer the typical italicized method (S. typhi). [10]


History

Salmonella was discovered by Theobald Smith in 1885 while inspector of the Bureau of Animal Industry (BAI). [16] Smith had been searching for the cause of common hog cholera and believed this organism to be the bacteria responsible. [16] It would later be learned that this organism (now known as Salmonella enterica) typically does not cause enteric symptoms in pigs, and was not really the bacteria that he was searching for. [10] But in any event, related bacteria of the genus Salmonella were eventually shown to cause gastroenteritis in other animals, including humans. [10] Although a pioneering research scientist in his own right, Smith named the bacteria after American veterinary pathologist Daniel Elmer Salmon, whom he worked under at the BAI. [16] The first diagnosis of Salmonella infection in a human occurred in 1896. [16] However, many historians posit that a devastating plague in Ancient Greece (430 B.C.) may be attributed to typhoid fever. [16] It is also possible that the English colony of Jamestown, Virginia, was wiped out by typhoid, with some 6000 settlers being killed between 1607 and 1624. [16] One of the first confirmed and most notable outbreaks associated with the disease happened in 1899 when around 13,000 British troops in South Africa succumbed to typhoid.[10]


Morphology and Physiology

Fig. 3 Growth on SS agar‎
Fig. 4 Growth on XLD agar‎

Salmonella are motile, rod-shaped bacteria with peritrichous flagella (surrounding the entire bacterial cell). [5,10] These Gram negative bacteria are typically between 2 and 5 micrometers in length, with a diameter of up to 1.5 micrometers. [11] The bacteria is nonsporeforming. Salmonella, along with most other enterobacteria, are facultative anaerobes: the bacteria possess the ability to but do not require the use of oxygen (although oxygen-utilization maximizes energy production). Being chemoorganotrophic, the bacteria use organic material as sources for energy. [9,11] This requires the oxidation of electron donors. Salmonella undergo asexual reproduction, dividing every 20 to 40 minutes when in normal growth conditions.[3,5,10]

Salmonella bacteria can survive for weeks in water and for several years in soil if subjected to favorable temperature, pH, and humidity. [3,11] Peak levels of Salmonella infections historically occur in the heat of summer months. [3,10,11] The bacteria are not destroyed by freezing, but Ultraviolet radiation and extreme heat can kill the cells. [3,10] Exposure to temperatures up to 55 °C (131 °F) for 90 minutes, or to 60 °C (140 °F) for 12 minutes will destroy the bacteria. [3,10]

Salmonellae posses three potential antigens: the H (flagellar) antigen; the O (somatic) antigen; and the Vi antigen (seen in only a few serotypes). [11] The H antigen has two potential forms called phase 1 and phase 2, and organisms can switch from one phase to the other. [11] The O antigens occur on the surface of the outer membrane and are determined by specific sugar sequences on the cell surface. [11] The Vi antigen is a surface antigen that covers the O antigen. [11] One of the few serotypes in which it is present is S. typhi.[11]

Salmonella bacteria can be cultured and plated on numerous selective and differential media, such as SS agar (Deoxycholate Citrate Agar), Bismuth Sulfate agar, Hektoen enteric (HE) medium, brilliant green agar and xylose-lisine-deoxycholate (XLD) agar. [13] Because most species of Salmonella produce hydrogen sulfide, Triple-Sugar Iron tubes may also be utilized. [13] Other results for numerous common biochemical tests are shown.

Lactose negative; acid and gas from glucose, mannitol, maltose, and sorbitol [13]

ONPG test negative (lactose negative) [13]

Indole test negative [13]

Methyl red test positive [13]

Voges-Proskauer test negative [13]

Citrate positive (growth on Simmon's citrate agar) [13]

Lysine decarboxylase positive [13]

Urease negative [13]

H2S produced from thiosulfate [13]

Phenylalanine and tryptophan deaminase negative [13]

Gelatin hydrolysis negative [13]


Pathogenicity and Virulence

Fig. 5 LPS‎

Another important characteristic of Salmonella bacteria is the presence of an endotoxin. This plays a major role the potential virulence of the bacteria. As is the case with Gram negative bacteria, the outer membrane contains lipopolysaccharides. This LPS comprises the endotoxin complex. The endotoxin complex consists of three components, an outer O-polysaccharide coat, a set, unchanging polysaccharide core (the R core), and an inner lipid A coat. [13] The repeating sugar units in the outer O-polysaccharide chains leads to extreme O antigen specificity and helps determine the virulence of the organism. [13] Salmonellae without the complete sequence of O-sugar repeat units are called rough (due to the rough appearance of the colonies) and they are typically avirulent or less virulent than the smooth strains. [11,13] The smooth strains have a full complement of O-sugar repeat units. [11,13] It is proposed that antibodies directed against the polysaccharide core may protect against infection by a wide variety of Gram-negative bacteria sharing a common core structure, or at the very least lessen their effects. [13] Finally, the endotoxin component of the cell wall (the inner Lipid A) can determine the severity of Gram-negative infections. [13] Reduced in small amounts while the cell grows, the lysing of a cell causes the rapid release of the toxin. This may lead to fever, activate complement pathways, alter immune response, etc. [10]

Salmonella is a facultative pathogen, capable of survival and reproduction both inside and outside of a host cell. [13] When invading a human host, the basic mode of infection is as follows:

The pathogenic bacteria passes through the gastric acid barrier of the stomach to invade the mucosal layers of the small and large intestine. [11,13] With the release of toxins, the involved epithelial cells release proinflammatory cytokines that lead to inflammation. [11,13] This causes the resultant diarrhea and mucosal destruction. [13] In the event that the bacteria disseminated from the intestines and into the bloodstream, the systemic disease results. [10,11] Nonspecific host defense against the disease involves gastric acidity, intestinal mucous, and lysozymes. [11] Specific defense can occur in the form of mucosal and systemic antibodies.[10,11]

Salmonella infections can be further subdivided into typhoidal and nontyphoidal serotypes (distinguishable by antigenic properties and character). There is varying specificity for the mechanisms of infection between the nontyphoidal and typhoidal. [9,10,11]

Nontyphoidal Infection

Nontyphoidal Salmonella is the major cause of the foodborne illness. This is the more common infection, and is typically limited to gastrointestinal disease. [3,10] However in developing countries, such as numerous countries sub-Sahara Africa, nontyphoidal Salmonella serotypes have been found to cause invasive bloodstream infections. [3,10] The main causative strains are S. typhimurium or S. enteritidis. [7] Generally speaking, nontyphoidal serotypes are zoonotic (transferable from animals to humans). [3,9,10] Infection occurs when a high concentration of the bacteria is ingested through the digestive tract. [11] Only a significant quantity (which still may very greatly, depending on the strain) will cause disease in healthy adults. [11] The actual infection process occurs after living Salmonellae (in addition to their toxins) reach the gastrointestinal tract. [9] While some of the bacteria are killed in the stomach (destruction being caused by gastric acidity), the surviving Salmonellae can enter the small intestine and multiply. [9,13] Salmonella, over time, has developed a level of tolerance to acidic environments that allows some of ingested bacteria to remain viable. [10] Some of the bacteria may also become trapped in mucus of the esophagus. [9,10] By the end of the incubation period, even nearby cells are affected by endotoxins released from the dead Salmonella. [9,10] This causes the gastroenteritis. [9,10,11]

Typhoidal Infection

The typhoidal serotypes (typically Salmonella Typhi and Salmonella Paratyphi A, B, or C) are adapted specifically to humans. [10, 11] This form infection is systemic: the bacteria pass through both the lymphatic system of the intestine and the bloodstream, from which various organs such as the liver and kidneys are affected. [10] Endotoxins then upset thermal regulation, causing vomiting and diarrhea. [10,11] Severe dehydration may occur in addition to altered water-salt metabolism. This can lead to hypovolemic shock. [10] Hypovolemic shock is caused by hypovolemia: a decreased volume of blood plasma due to the loss of sodium ions. It is also possible for septic shock to occur. This is due to low blood pressure stemming from a reduced cardiac output (a direct result of the actual dehydration). [10,11]


Transmission

Salmonella bacteria can dwell in the intestinal tracts of humans, birds, and other animals. These reservoirs may hold onto the bacteria for varying, and in some cases extended, lengths of time. Human infection is typically the result of eating foods contaminated with animal feces. Salmonella bacteria is commonly found in beef, raw poultry, cheese, eggs, dry cereal, ice cream premix, sprouts, juice, cantaloupes, and other fresh vegetables. [7,10] But any food that comes in contact with the bacteria can become cross-contaminated (such as food prepared on surfaces that previously were in contact with raw meat). Consumption of polluted water can also lead to infection. This is most common in standing water or infrequently utilized areas, but can also occur in water fountains, showerheads, etc. [7,10,11] Human-to-human transmission can occur when an infected person's feces, typically through improper hygiene, contaminate food or come into direct contact with another person (such as a handshake). Salmonella can also be acquired directly from contact with animals such as birds, fish, dogs, cats and numerous reptiles. [1,7]


Symptoms and Diagnosis

Fig. 6 Symptoms of Salmonellosis‎

Salmonellosis, when resulting from nontyphoidal serotypes of the bacteria, results in gastroenteritis: enteric inflammation. [3] The incubation period is usually between 6 and 72 hours. [10] The main acute symptoms associated with Salmonellosis are diarrhea, abdominal cramps, and fever. [1,3,10] These symptoms typically appear eight hours to three days after the intial infection. [1,3,10] Additional symptoms of chills, headache, and nausea may also appear. [10] Typically, (and specifically with the nontyphoidal infections), the symptoms last four to seven days before passing without complication. [1,10]

A diagnosis of Salmonellosis can be confirmed by organism isolation from the stool or blood in a clinical specimen. [10] While a reportable foodborne illness, disease surveillance is passive (the investigator waits for the reports to come in) and thus the number of diagnosed cases may be underreported. [10] This is especially true for isolated cases in rural areas. [3,10]


Treatment

As previously stated, Salmonellosis usually passes in under a week for most individuals. [3] At the onset of diarrhea, hydration is necessary to replenish fluids and electrolytes. Symptomatic treatment with acetaminophen for pain and fever may be beneficial. [10] It may also help to try eating five to six small meals a day. [1,10] A progressive diet (clear liquids to full liquids to soft foods) will aid in assessing tolerance. [11] If the infection does spread to the bloodstream, antibiotic ampicillin (a beta-lactam antibiotic that is similar to amoxicillin in terms of spectrum and activity). [10,11] In case of severe infection, fluoroquinolones (synthetic broad-spectrum antibacterial drugs), and third-generation cephalosporins (subgroup of β-lactam antibiotics called cephems) may be utilized. [10,11] Generally speaking, use of antibiotics to treat uncomplicated gastroenteritis is avoided. This is due to the fact that exposure may promote antibiotic resistance. [10] However, exceptions are made for infants, the elderly, and severely immunocompromised individuals (such as those with the human immunodeficiency virus). [10,11]


Prevention

Numerous measures can be taken to prevent Salmonellosis. Major control factors include:

-Adequate temperature control and food storage: Keep your refrigerator below 40°F and refrigerate food that will spoil. Ensure that cooked foods reach a safe internal temperature: 145°F for whole meats, 160°F for ground meats, and 165°F for poultry. [10]

-Maintaining a sanitary kitchen

-Avoiding the consumption of raw or undercooked meat or eggs

-Pasteurizing all milk and egg products [10]

-Educating food handlers on proper sanitation methods [10]

-Carefully washing hands with soap after handling pets, turtles, lizards, or other reptiles

-Reporting suspected outbreaks to your local health department [10]


Salmonella usually remains in the intestines for anywhere from five weeks to several months. Some individuals can become chronic carriers of Salmonella bacteria. [6,7]

In specific regard to nontyphoidal infections, antibiotics neither cure nor prevent Salmonellosis; they simply can aid in lessening the effects. But with the proliferation of antibiotic-resistant strains of Salmonella in underdeveloped countries, such as those in sub-Saharan Africa, there is growing urgency to develop an effective vaccine. [10] Current research has led to the study and identification of 8 different antigenic molecules from human and mouse infections. [9,10] From careful observation and experimentation, viable vaccines are being tested in chickens, with the hope of eventually obtaining a vaccine suitable for humans. [10]


Complications/Sequelae

As previously stated, those who are immunocompromised are significantly more likely to face complications or secondary infections as a result of Salmonellosis. [10] But even for otherwise healthy individuals, complications may occur in the rare event that the Salmonella infection reaches the bloodstream (even with nontyphoidal infections). Known as bacteremia, this can cause infected tissue throughout the body. [15] Endocarditis, meningitis, and osteomyelitis and can result. [15] Arthritic symptoms may appear up to a month after the initial Salmonellosis symptoms. [10] Known as Reiter’s syndrome, this can cause joint pain, eye irritation, and painful urination. [10]

Fig. 7 Typhoid fever rash‎

For typhoid serotype infections, typhoid fever may result. Typhoid fever, caused by Salmonella typhi specifically, is contracted through contact with food, water, sewage, etc. that is contaminated with the bacteria. [10] S. typhi lives only in humans, and thus is transferred from human to human. [10] Although not common in the United States, it is still a major issue in developing countries. [10] This is especially true in places where hygiene is not emphasized. Once consumed, the bacteria multiply and and spread to the bloodstream. Initial symptoms include sustained fever, weakness, stomach pains, headache, and a flat rash of rose-colored spots. [10] By the third week, numerous other complications may present : intestinal hemorrhage due to bleeding in congested Peyer's patches, encephalitis (swelling of the brain), metastatic abscesses, cholecystitis (inflammation of the gallbladder), endocarditis (inflammation of the endocardium) and osteitis (bone inflammation). [10] A stool sample is needed to confirm typhoid fever. [10] Treatment of strains for which is resistance is uncommon is typically very effective; fluoroquinolone, ampicillin, chloramphenicol, and third generation cephalosporins have all been utilized. [10] However, resistance to these drugs is now common with the rise of multi-drug resistant typhoid. [10] Yet with prompt treatment, the worldwide fatality rate is under 1%. [10] Prevention of typhoid is possible through vaccination. British bacteriologist Almroth Edward Wright developed the first effective typhoid vaccine in 1896. [10] Today, there are two effective types: Ty21a, which is a live vaccine given orally, and Vi capsular polysaccharide vaccine, which is an injectable subunit vaccine. [6, 10, 11]

Similar to typhoid fever is paratyphoid fever. The causative strains of this related enteric illness are the Salmonella serotypes S. Paratyphi A (S. schottmuelleri) , S. Paratyphi B (S. pullorum), and S. Paratyphi C (S. hirschfeldii). [10] Presenting symptoms resemble typhoid fever but appear more abruptly, with milder symptoms and a lessened duration. [10] Infection typically leads to a sustained fever, headache, abdominal pain, , a non productive cough (in early stage of illness), a slowed heart rate, and hepatosplenomegaly (an enlargement of the liver or spleen). [10] Treatment with antibiotics such as azithromycin is usually an effective defense against the illness. [10] The typhoid vaccine will not protect against exposure to any of the paratyphoid strains. [10]


Statistics and Outbreaks

Current estimations attest that around 40,000 cases of Salmonella infection are reported in the United States annually, but potential underreporting limited time to compile data tempers the veracity of many up-to-date statistics. [10] Data obtained from sources such as the Center for Disease Control give perhaps the most accurate representations of past numbers. The CDC’s Foodborne Disease Outbreak Surveillance System performs annual reports that compile data and statistics for reported foodborne illnesses in the United States. A foodborne disease outbreak is defined by two or more people getting the same illness from the same contaminated source. [10] From 2009 to 2010, public health departments reported 1,527 foodborne disease outbreaks, resulting in 29,444 cases of illness, 1,184 hospitalizations, and 23 deaths. [10] Among the 790 outbreaks with a laboratory-confirmed illness, Salmonella accounted for 30% of outbreaks. [10] Out of the 29,444 outbreak-related illnesses, 1,184 led to hospitalization. [10] Salmonella caused the most outbreak-related hospitalizations, with 49%. [10] Among the 23 reported deaths, 5 were attributed to Salmonella. [10] The following shows the the foods primarily responsible for the majority of the illnesses, hospitalizations, and deaths:

Illnesses Salmonella in eggs (2231 illnesses) [10] Salmonella in sprouts (493 illnesses) [10] Salmonella in vine-stalk vegetables (422 illnesses) [10] Hospitalizations Salmonella in vine-stalk vegetables (88 hospitalizations) [10] E. coli O157 in beef (46 hospitalizations) [10] Salmonella in sprouts (41 hospitalizations) [10] Deaths E. coli O157 in beef (3 deaths) [10] Salmonella in pork (2 deaths) [10] Listeria in dairy (2 deaths) [10]

During the same time period, 21 of the 38 multistate outbreaks reported were the result of Salmonella outbreaks. [10] In particular, one large 2010 outbreak of Salmonella infections caused nearly 2000 illnesses. [10] The foods most often responsible were beef (13%), dairy (12%, nearly all unpasteurized), fish (12%), and poultry (11%). [10]



Timeline of recent selected cases in the United States: (CNN.com) [15]

Foster Farms brand chicken - 2013 Multistate outbreak of of Salmonella Heidelberg linked to Foster Farms brand chicken. [15] A total of 278 persons in 17 states have been infected. [15]

October 7, 2013 - The U.S. Department of Agriculture issues an alert about illnesses caused by strains of Salmonella Heidelberg that are associated with raw chicken products produced by Foster Farms in California. [15]

Live Poultry - March 2013 Multistate outbreak of Salmonella typhimurium infections linked to contact with live poultry purchased from feed stores and mail-order hatcheries. [15] A total of 316 persons in 37 states have been infected. [15]

April 25, 2013 - The CDC announces that public health and agriculture officials across several states are investigating an outbreak of human Salmonella typhimurium infections linked to contact with live poultry. [15]


Interesting Facts

Fig. 8 Gross

-Approximately 400 people die each year with acute salmonellosis. [10]


-Salmonellosis rarely affects the taste, smell, or appearance of food. [10]


- In 1975, the Food and Drug Administration established a ban on the sale of baby turtles possessing a carapace smaller than four inches. This law was enacted because an estimated 250,000 young children were found to be infected with salmonellosis handling these small turtles, or even putting them in their mouths. [7,10]


-Currently 0.01% of all eggs contain Salmonella enteritidis. [10]


-Typhoid Mary. Mary Mallon (September 23, 1869 – November 11, 1938), was the first person in the United States identified as an asymptomatic carrier of typhoid fever. [12] She was presumed to have infected 49 people, three of whom died, over the course of her career as a cook. She was twice forced into isolation by public health authorities and died after a total of nearly three decades in isolation. [12] Initially tracked and questioned by George Soper, a civil engineer with experience in typhoid fever outbreaks, Mary assumed she was healthy (having never shown any symptoms or effects of typhoid) and became increasingly enraged at inquiries for blood and stool samples. [12] Soper gave this account:

Fig. 9 Typhoid Mary‎

“I had my first talk with Mary in the kitchen of this house. . . . I was as diplomatic as possible, but I had to say I suspected her of making people sick and that I wanted specimens of her urine, feces and blood. It did not take Mary long to react to this suggestion. She seized a carving fork and advanced in my direction. I passed rapidly down the long narrow hall, through the tall iron gate, . . . and so to the sidewalk. I felt rather lucky to escape.”

Eventually, government intervention forced Mallon to come in for testing. She was taken to the Willard Parker Hospital in New York. [12] There, samples were taken and examined; typhoid bacilli was found in her stool. [12] The health department then transferred Mallon to an isolated cottage on North Brother Island. [12] After over a year in isolation and an unsuccessful lawsuit levied against the Health Administration, Mallon was released after swearing to change occupations. [12] However, she eventually returned to her occupation as a cook, utilizing a pseudonym. [12] When another outbreak occurred at her place of work ( 25 illnesses and 2 deaths), she was sent back to the island, where she would die 23 years later. [12]


References

1. Reuman, Peter D., M.D., M.P.H.(2013). Salmonella infection. Magill’s Medical Guide. Web.

In this article, Dr. Reuman details the causes, symptoms, duration and treatments of Salmonellosis. The apparent purpose is to lend a comprehensive overview of basic notable facts about the infection. Reuman is currently a pediatric infectious disease doctor.


2. Mughini-Gras, L., and R. Enserink. "Risk Factors for Human Salmonellosis Originating from Pigs, Cattle, Broiler Chickens and Egg Laying Hens: A Combined Case-control and Source Attribution Analysis." Public Library of Science 9.2 (2014): 1932-6203. Web.

The authors of this article are all researchers for the National Institute for Public Health and Environment, as well as for the Centre for Infectious Disease and Control, located in the Netherlands. The purpose was to delineate the human risk factors of Salmonellosis exposure from pigs, cattle, broilers and layers/eggs. They concluded that different reservoirs yield different associated risk factors, and thus that human infection may occur through different transmission pathways.


3. "Salmonellosis." Columbia Electronic Encyclopedia 6th. Columbia University Press, Sept. 2013. Web.

This reference article gives a simple synopsis about the infectious diseases caused by intestinal bacteria of the genus Salmonella. Highlighted are conditions such as typhoid fever, blood poisoning, and food poisoning.


4. Foley, Steven L., and Rajesh Nayak. "Population Dynamics of Salmonella Enterica Serotypes in Commercial Egg and Poultry Production." American Society for Microbiology (May 2011). Web.

Headlined by Steven Foley of the National Institute for Technological Research, this article explores both the genetic and host-related factors that contribute to changes in Salmonella populations. Highlighted is exposure to Salmonella enterica and its affect on processed poultry. The article also includes strategies to potentially limit colonization of this bacteria.


5. Bäumler, A. J. "EPIDEMIOLOGY:Enhanced: Tracing the Origins of Salmonella Outbreaks." Science 287.5450 (2000): 50-52. Print.

In this article, Bäumler and his colleagues postulate that the proliferation of Salmonella outbreaks is due in large part to the serotype S. enteritidis. This determination was made utilizing retrospective analysis of empirical data. The theory proposed states that S. enteritidis is capable of filling a niche left by other common Salmonella strains for which a common antigen abounds.


6. Evangelopoulou, Grammato, Spyridon Kritas, Alexander Govaris, and Angeliki R. Burriel. "Animal Salmonelloses: A Brief Review of “Host Adaptation and Host Specificity” of Salmonella Spp." Veterinary World 6.10 (2013): 703-08. Print.

This article explores the host specificity of Salmonella serovars. The ever increasing abundance of this disease is discussed in conjunction with mechanisms for both the spread and persistence of Salmonella in new hosts. Also covered is the manner in which virulence determinants in Salmonella serovars can be used as virulence determinants for general bacteria for certain species.


7. Vora, Neil M., Kristine M. Smith, Catherine C. Machalaba, and William B. Karesh. "Reptile- and Amphibian-associated Salmonellosis in Childcare Centers, United States." Emerging Infectious Diseases 18.12 (2012): 2092-094. Print.

The authors of this article seek to show the general low level of awareness shown by the public in regard to Salmonella infections. Collected data displays inadequate steps being taken to prevent transmission in childcare centers across the United States. The article seeks to highlight the numerous discrepancies between state regulations, and the potentially harmful consequences.


8. Lee, M.b., and J.d. Greig. "A Review of Nosocomial Salmonella Outbreaks: Infection Control Interventions Found Effective." Public Health 127.3(2013): 199-206. Print.

The purpose of this study was to observe both the transmission and effect of nosocomial Salmonellosis outbreaks, in hopes of developing profitable methods of control and prevention. The authors systematically reviewed hospital outbreaks from 1995 until 2011. Their conclusions showed that added emphasis must be placed on food handling, worker training, and temperature monitoring.


9. Acheson, D., and E. L. Hohmann. "Nontyphoidal Salmonellosis." Clinical Infectious Diseases 32.2 (2001): 263-69. Print.

In this article, the authors show how nontyphoidal Salmonella is the cause of gastroenteritis, bacteremia, and subsequent focal infection. They give a breif overview of both the disease and both problems and trends associated with Salmonellosis.


10. "Salmonella." Centers for Disease Control and Prevention. April 2014. Web.

The premier authority on infectious diseases, the Center for Disease Control provides an excellent resource for information, facts, research, and outbreaks concerning Salmonellosis. This includes providing tools for prevention, locations of trouble areas, and a comprehensive history of the infection as it pertains to the United States and the world.


11. Giannella, Ralph. "Salmonella." Medical Microbiology 4.0 (1996): Ch. 21. Print

Dr. Giannella gives an in-depth anaylsis of the Salmonella bacteria and its modes on infection on human hosts.


12. Leavitt, Judith Walzer. Typhoid Mary: Captive to the Public's Health. Boston: Beacon Press, 1996.

This article give a biographical account of the life of Mary Mallon and how she, as an asymptomatic carrier, became known throughout history as Typhoid Mary.


13. Todar, Kenneth. "Salmonella and Salmonellosis" Todar's Online Textbook of Bacteriology. 2012. Web

This online textbook by Dr. Kenneth Todar is an excellent resource for both pictures and data about both the Salmonella organism as well as the condition it causes, Salmonellosis.


14. Robinson, Sam. "The Big Five: Most Common Salmonella Strains in Foodborne Illness Outbreaks" Food Safety News. Food Safety News. N.p., 19 Aug. 2013. Web.

In this article, Sam Robinson discusses the five most common strains of Salmonella as well as how they are normally contracted. This focuses on cases in the United States.


15. Salmonella Infection. Mayo Foundation for Medical Education and Research. CNNHealth. 16 April, 2011. Web

This article gives comprehensive information about the disease Salmonellosis. It also delves into diagnosis, treatment, and potential risk factors. Details about recent cases involving Salmonella are also provided.


16. Shultz, Myron. "Emerging Infectious Diseases." National Center for Biotechnology Information. 2008. Web

In this article written by Myron Shultz, numerous details about the history of Salmonella infections are given. This includes information about Theobald Smith, who discovered the bacteria.

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