Common Foodborne Pathogens - I

Salmonella Risk Profile 

Salmonella is among one of the predominant causes of common foodborne bacterial infections around the world which causes diarrhea, fever abdominal cramp and vomiting. Occasionally, it may infected to bloodstream leading to multiple organ infections, reactive arthritis in severe infections and death. The primary sources are raw animal products, fruit and vegetables in many recent outbreaks.

Salmonella sp. is a motile, gram-negative, facultative anaerobic rod-shaped bacterium in the family Enterobacteriaceae and the family Salmonellae, which does not form spores. Growth occurs at 5 – 47°C, and the organism is heat sensitive. It is a zoonotic organism, which may be found in different animals’ guts. According to CDC website estimates, Salmonella spp. cause about 1.35 million infections, 26,500 hospitalizations, and 420 deaths in the United States every year. Food is the major source for most of these infections.
The genus Salmonella is divided into two species that can cause sickness in humans: 

S. enterica 

S. bongori 

 

Salmonella enterica is the greatest public health concern, which comprised of six subspecies: 

S. enterica subsp. enterica (I)

S. enterica subsp. salamae (II)

S. enterica subsp. arizonae (IIIa)

S. enterica subsp. Diarizonae (IIIb) 

S. enterica subsp. houtenae (IV)

S. enterica subsp. indica (VI)

 
Salmonella is further subdivided into serotypes, based on the Kaufmann-White typing scheme first published in 1934, which differentiates Salmonella strains by their surface and flagellar antigenic properties. Salmonella spp. are commonly referred to by their serotype names, i.e., Salmonella enterica subsp. enterica is further divided into numerous serotypes, including S. Enteritidis and S. Typhimurium, which are common in the United States. When Kaufmann first proposed the scheme, 44 serotypes had been discovered, but as of 2007, the number of serotypes discovered was 2,579.
 
Sources 

Salmonella is widely dispersed in nature, which can colonize in the intestinal tracts of vertebrates, including livestock, wildlife, domestic pets, and humans, and may also live in environments such as pond-water sediment. The spread occurs through the fecal-oral route and contact with contaminated water, where certain protozoa may act as a reservoir for the organism. The bacteria may, for example, contaminate meat, farm-irrigation water, which contaminates produce in the field, soil and insects, factory equipment, hands, and kitchen surfaces and utensils. 
 
S. Typhi and S. Paratyphi A are only found in human hosts, thus usual sources of these organisms in the environment are drinking and/or irrigation water contaminated by untreated sewage. Hence, it is highly recommended that only potable water and cooked vegetables be consumed in areas where these organisms are endemic. 
 
Nevertheless, various Salmonella species have been isolated from the outside of eggshells, but S. Enteritidis has been isolated inside the egg on the albumen/egg white side of the yolk-sack membrane (vitelline membrane), which strongly suggest vertical transmission. The deposition of the organism usually occurred through an infected hen, before shell formation. Outbreaks also have been linked to the handling of certain animals occasionally, who kept as pets, such as turtles, frogs, and chicks. 
 

Food Sources – Traditionally Salmonella was considered as being associated with animal products in the past, but current data has confirmed that fresh produce also has been the source of major outbreaks. The organism also survives well on low-moisture foods, such as spices, which have been the vehicles for large outbreaks. The long list of foods that have been linked to Salmonella infection include meats, poultry, eggs, milk and dairy products, fish, shrimp, spices, yeast, coconut, sauces, freshly prepared salad dressings made with unpasteurized eggs, cake mixes, cream-filled desserts and toppings that contain raw egg, dried gelatin, peanut butter, cocoa, produce (fruits and vegetables, such as tomatoes, peppers, and cantaloupes), chocolate, etc.

 

Cross Contamination – Cross contamination usually occurs when Salmonella is spread from a contaminated source such as contaminated food or an infected food handler or animal to other foods or objects in the environment. The criterion may occur when potentially contaminated raw meats, poultry, seafood, produce, or eggs which are not kept separate from each other during preparation or cooking, or when a food handler does not adequately clean utensils, surfaces, equipment, and hands after they have come into contact with those products. The contamination can spread to factory and equipment surfaces, as well as to kitchen surfaces and utensils, where cross-contamination may occur at any point in the food production process. Cross-contamination also may occur from handling pets or wildlife, such as turtles or frogs or their water, soil, or food and water bowls, then handling food, food-preparation utensils, or other objects in the environment. 

 
Disease 

Salmonella can cause two types of sicknesses, depending on the serotype; 

1. Non-typhoidal salmonellosis 
2. Typhoid fever 

 Non-typhoidal Salmonellosis 
Gastrointestinal complications of non-typhoidal salmonellosis, which causes nausea, vomiting, diarrhea, cramps, and fever, with symptoms generally lasting a couple of days and tapering off within a week. According to the Centers for Disease Control and Prevention (CDC) estimates that 1,027,561 cases of domestically acquired non-typhoidal salmonellosis occur annually in the United States when under-reporting and under-diagnosis are taken into account. The symptoms of non-typhoidal salmonellosis can be quite unpleasant, but the disease is generally self-limiting among healthy people with intact immune systems, although it can cause life-threatening illness even in healthy people. Caused by serotypes other than S. Typhi and S. Paratyphi A. 
 

Mortality: 

Generally less than 1%; however, S. Enteritidis has a 3.6% mortality rate in outbreaks in nursing homes and hospitals, with the elderly being particularly affected. 

 

Onset: 

6 to 72 hours after exposure. 

 

Infective dose: 

As low as one cell, depending on age and health of host and strain differences among members of the genus. 

 

Symptoms: 

Nausea, vomiting, abdominal cramps, diarrhea, fever, headache. 

 

Duration: 

Symptoms generally last 4 to 7 days, with acute symptoms usually lasting 1 to 2 days or longer, depending on host factors, the dose ingested, and strain characteristics. 

 

Complications: 

Dehydration and electrolyte imbalance may occur as a result of diarrhea and vomiting. That can lead to death in the very young, the elderly, and the immunocompromised, if not treated promptly. 

 

In 2% of culture-proven cases, reactive arthritis (i.e., arthritis from an immune reaction to the infection – an autoimmune response – rather than directly from the infection itself) may follow 3 to 4 weeks after the onset of acute symptoms. Indications of reactive arthritis may include, for example, joint inflammation, urethritis, uveitis, and/or conjunctivitis. 

 

Non-typhoidal Salmonella can sometimes escape from the gastrointestinal tract into the body and cause blood poisoning (septicemia) or infect the blood, internal organs, and/or joints (bacteremia). S. Dublin is sometimes associated with this complication. 

 

Route of entry: 

Oral – through ingestion of contaminated food, fecal particles, or contaminated water. 

 

Pathway: 

Penetration and passage of Salmonella organisms from the gut lumen into the epithelium of small intestine, where inflammation occurs. There is evidence that enterotoxin may be produced, perhaps within enterocytes.

 
Typhoid Fever 

The typhoidal illness causes high fever, diarrhea or constipation, aches, headache, and lethargy (drowsiness or sluggishness), a rash, and death of up to 10% of people who don’t get treatment. The typhoidal infection usually is associated with sewage-contaminated drinking water, or crops irrigated with sewage‐contaminated water. The bacterium is hard to wash off of food, even with soapy water, so important measures for preventing foodborne disease from Salmonella include thorough cooking, hand washing, keeping raw foods separated from cooked foods, and keeping foods at the correct temperature. Nonetheless, Salmonella can spread into other organs and cause very serious infirmity in people with weak immune systems. On the other hand, Typhoid fever is more serious and has a higher mortality rate than non-typhoidal salmonellosis. According to the CDC, S. enterica serotype Typhi, a mean of 1,821 cases occur annually in the United States, and the additional cases are associated with foreign travel. Caused by serotypes S. Typhi and S. Paratyphi A, both of which are found only in humans. 
 

Mortality: 

Untreated, as high as 10%.

 

Onset: 

Generally 1 to 3 weeks, but maybe as long as 2 months after exposure. 

 

Infective dose: 

Fewer than 1,000 cells.

 

Symptoms: 

High fever, from 103° to 104°F; lethargy; gastrointestinal symptoms, including abdominal pains and diarrhea or constipation; headache; achiness; loss of appetite. A rash of flat, rose-colored spots may occur in the skin. 

 

Duration: 

Generally 2 to 4 weeks. 

 

Complications: 

Septicemia, with the colonization of other tissues and organs; e.g., may lead to endocarditis. Septic arthritis may occur, in which the infection directly affects the joints and may be difficult to treat. Chronic infection of the gallbladder may occur, which may cause the infected person to become a carrier. 

 

Route of entry: 

Oral through ingestion of contaminated food, fecal particles, or contaminated water. 

 

Pathway: 

Penetration and passage of typhoid Salmonella organisms from the gut lumen into the epithelium of small intestine and the bloodstream (i.e., septicemia), which may carry the organisms to other sites in the body, where inflammation occurs. There is evidence that enterotoxin may be produced, perhaps within enterocytes. 

 
Diagnosis 
Serological identification of cultural isolates from the stool. 
Genetic identification of approximately 100 Salmonella serotypes from pure culture is now possible, but the remaining 2,400-plus serotypes can be identified only through traditional serotyping.

 
Growth Factors 

Temperature:

           Minimum – 5.2°C Maximum – 462°C (Optimum 35C – 43°C)

pH:

Minimum – 3.7 Maximum – 9.5 (Optimum 7 – 7.5)

Water Activity (aW):

Minimum – 0.94 Maximum – 0.99 (Optimum >0.99)

Water Phase Salt:

Maximum – 8%       

 
Target Populations 

Anyone, of any age, may become infected with Salmonella, but immunocompromised people are highly vulnerable to the disease, such as the very young and the elderly, people with HIV or chronic disorders, and people on critical medications; i.e., chemotherapy for cancer or the immunosuppressive drugs used to treat some types of arthritis. People with HIV are estimated to have salmonellosis at least 20 times more than does the general population and tend to have recurrent episodes. 

 
Food Analysis 
Isolation and detection methods have been developed for many foods, having a prior history of Salmonella contamination. The conventional culture and identification methods may require 4 to 6 days for presumptive results. There are several rapid methods available to screen foods that require 1 to 2 days, which include antibody and molecular (DNA or RNA) based assays, but in most cases, require a cultural means to confirm the presence of Salmonella, for regulatory purposes. 
 
Reference:
FDA Bad Bug Book, Foodborne Pathogenic Microorganisms and Natural Toxins. Second Edition. 2013
Preventive Controls for Human Foods. 2016

www.cdc.gov