Nguyễn Thuý Hằng
Junior Member
SALMONELLA
What is salmonella?
Salmonella bacteria cause much of the food poisoning in the world, including an estimated four million cases of salmonellosis in the United States each year. In Illinois about 1,500 to 2,500 cases of this foodborne illness are reported each year.
Salmonella is a general name for a group of about 2,000 closely related bacteria that cause illness by reproducing in the digestive tract. Each salmonella subgroup, or serotype, shares common antigens and has its own name.
How is it spread?
Salmonella bacteria is found wherever animals live. The bacteria can withstand hot and cold weather, rain and drought. Animals consume salmonella from the soil or contaminated processed feed. The bacteria are then shed alive in the infected animal's feces. The animal may or may not be sick, depending on the bacteria's serotype.
During slaughtering and processing, salmonella may contaminate animal carcasses. According to U.S. Department of Agriculture estimates, nearly 40 percent of the American poultry supply, 12 percent of the pork and 5 percent of the beef are contaminated with salmonella.
In recent years, fresh fruits and vegetables have been implicated in outbreaks of salmonellosis. Tomatoes were identified as the culprit in 1990 and 1993 and, in 1990 and 1991, cantaloupes were linked to salmonellosis. Investigations of these incidents did not identify the source of contamination. It possibly could have occurred in the fields where the produce was grown, during processing after harvest or during handling in the distribution system.
Person-to-person transmission of salmonella occurs when a carrier's feces, unwashed from his or her hands, contaminates food during preparation or through direct contact with another person. Usually the illness comes from food contaminated with animal feces found on or in raw meats, eggs, fish and shellfish and, most commonly, in poultry. Salmonella also may be found in raw milk or in milk that is contaminated after pasteurization. The bacteria also may be carried by pets birds, fish, dogs, cats and turtles. The U.S. Food and Drug Administration banned the sale of turtles smaller than 4 inches wide in 1975 to prevent the spread of salmonella.
Since early 1950, farmers have administered low doses of penicillin and tetracycline to cows, chickens and pigs to prevent infection and promote growth. As a result, the bacteria in these animals develop a resistance to the drugs. When these drugs are used to treat infections in humans who have eaten meat from treated animals, the drugs are not as effective as they might be. The U.S. Centers for Disease Control and Prevention estimates that between 20 percent and 30 percent of all salmonella cases involve bacteria resistant to antibiotics.
What are the symptoms?
A person may contract salmonellosis many times in his or her life and not always recognize it. Often it is mistaken for the "stomach flu." Symptoms, which last from 24 hours to 12 days, include headache, muscle aches, diarrhea, vomiting, rumblings in the bowels, chills, fever, nausea and dehydration. They usually appear six to 72 hours after ingestion, but carriers have no symptoms. Children younger than 1 year old, people who have had ulcer surgery or take antacids and those whose immune systems have been weakened by other ailments are most susceptible.
Salmonellosis is seldom fatal (the fatality rate is less than 1 percent). Two or three weeks after being infected with salmonella, one in 10,000 cases develops reactive arthritis or Reiter's syndrome as a complication. These patients also may develop an inflammation of the urethra and eyes.
How is salmonellosis treated?
Fluids are recommended to prevent dehydration because the diarrhea that flushes bacteria out of the body drains a great deal of liquid. Pain relievers and fever reducers may make the person more comfortable.
Most cases of salmonellosis are not treated with antibiotics. In fact, antibiotics may prolong the period during which the person can infect others. Also, antibiotics actually may bring on salmonellosis symptoms by upsetting the bacterial balance in the intestines. Antibiotics sometimes are prescribed for infants, the chronically ill and the elderly to prevent salmonella-triggered local infections or bacteremia. Antibiotics also are needed when the bacteria cause meningitis or infections of the blood stream.
Can salmonellosis be prevented?
People are far more likely to contract salmonellosis at home than in a restaurant, so be sure to handle food safely.
Salmonella are killed when food is thoroughly cooked. This means cooking ground beef to at least 155 degrees and making sure all food is cooked properly. Once cooked, any food held in a buffet should be kept hotter than 140 degrees. Cross-contamination--where food is contaminated in the kitchen after it has been cooked--may be avoided by using different utensils, plates, cutting boards and counter tops before and after cooking. Cooked food that stands at room temperature for a long time, especially poultry, is at risk.
Defrost frozen food in the refrigerator or microwave. Refrigerator temperatures should be kept colder than 40 degrees. Rinse poultry in cold water before cooking. Avoid raw milk, raw hamburger meat and raw eggs (many recipes, such as those for homemade ice cream, call for eggs with no subsequent cooking; substitute pasteurized eggs in these recipes). Food contaminated with salmonella may look, smell and taste normal.
Because fruits and vegetables have now been identified as a source of salmonella, it is important that these food items be thoroughly washed in running water before they are eaten.
Wash utensils and wooden cutting boards thoroughly with hot, soapy water. Salmonella may lie dormant for a year or more and then "wake up" when food is present. They also may live in the cut marks on a wooden cutting board. Use an acrylic board that can go in the dishwasher. Rub down or spray wooden boards with a solution of one ounce bleach to one gallon water and allow to air dry. Cutting boards for raw meat and poultry should not be used for cheese, raw vegetables and other foods that will not be cooked before being served.
To prevent the spread of salmonella, wash hands thoroughly after using the bathroom and before handling food. Do not allow an infected person to handle food or work in the kitchen.
Salmonella Nomenclature
The genus Salmonella is a member of the family Enterobacteriaceae, It is composed of bacteria related to each other both phenotypically and genotypically. Salmonella DNA base composition is 50-52 mol% G+C, similar to that of Escherichia, Shigella, and Citrobacter. The bacteria of the genus Salmonella are also related to each other by DNA sequence. The genera with DNA most closely related to Salmonella are Escherichia, Shigella, and Citrobacter. Similar relationships were found by numerical taxonomy and 16S ssRNA analysis.
Salmonella nomenclature has been controversial since the original taxonomy of the genus was not based on DNA relatedness, rather ?names were given according to clinical considerations, e.g., Salmonella typhi, Salmonella cholerae-suis, Salmonella abortus-ovis, and so on. When serological analysis was adopted into the Kauffmann-White scheme in 1946, a Salmonella species was defined ?as "a group of related fermentation phage-type" with the result that each Salmonella serovar was considered as a species. Since the host-specificity suggested by some of these earlier names does not exist (e.g., S. typhi-murium, S. cholerae-suis are in fact ubiquitous), names derived from the geographical origin of the first isolated strain of the newly discovered serovars were next chosen, e.g., S. london, S. panama, S. stanleyville.
Susequently it was found that all Salmonella serovars form a single DNA hybridization group, i.e., a single species composed of seven subspecies, and thenomenclature had to be adapted. To avoid confusion with the familiar names of serovars, the species name Salmonella enterica was proposed with the following names for the subspecies:
enterica ?I
salamae II
arizonae IIIa
diarizonae IIIb
houtenae IV
bongori V
indica VI
Each subspecies contains various serovars defined by a characteristic antigenic formula.
Since this formal Latin nomenclature may not be clearly understood by physicians and epidemiologists, who are the most familiar with the names given to the most common serovars, the common serovars names are kept for subspecies I strains, which represent more than 99.5% of the Salmonella strains isolated from humans and other warm-blooded animals. The vernacular terminology seems preferred in medical practice, e.g., Salmonella ser. Typhimurium (not italicized) or shorter Salmonella (or S.) Typhimurium.
?
You are here: News & Events /
New Salmonella Finding—
Inter-Bacterial Communication!
Salmonella enteritidis.
(K8732-2) Talking bacteria may sound bizarre, but microorganisms do have a primitive form of communication--much as some insects use pheromones to lure a mate or signal an attack. An Agricultural Research Service scientist found this happens with Salmonellabacteria, and her discovery could have big implications for food safety.
Veterinarian Jean Guard-Petter, who is in ARS' Southeast Poultry Research Unit at Athens, Georgia, found that the food pathogen Salmonella enteritidis uses acyl-homoserine lactone, or AHL, as its chemical "call to arms."
"This chemical tells cells to rewrite their genetic programming," says Petter. "It enhances their ability to grow as much as a hundredfold and signals cells to produce molecules that increase virulence—the ability to invade living things and cause disease."
Over the last 15 years, occurrences of S. enteritidis food poisoning have increased fourfold in the United States and fortyfold in Europe.
This large bacterial colony of Salmonella
enteritidis grew rapidly (62 millimeters
in diameter in 16 hours) and readily contaminated eggs when given to chickens
by injection but not when given by mouth.
(K8732-1)
What is salmonella?
Salmonella bacteria cause much of the food poisoning in the world, including an estimated four million cases of salmonellosis in the United States each year. In Illinois about 1,500 to 2,500 cases of this foodborne illness are reported each year.
Salmonella is a general name for a group of about 2,000 closely related bacteria that cause illness by reproducing in the digestive tract. Each salmonella subgroup, or serotype, shares common antigens and has its own name.
How is it spread?
Salmonella bacteria is found wherever animals live. The bacteria can withstand hot and cold weather, rain and drought. Animals consume salmonella from the soil or contaminated processed feed. The bacteria are then shed alive in the infected animal's feces. The animal may or may not be sick, depending on the bacteria's serotype.
During slaughtering and processing, salmonella may contaminate animal carcasses. According to U.S. Department of Agriculture estimates, nearly 40 percent of the American poultry supply, 12 percent of the pork and 5 percent of the beef are contaminated with salmonella.
In recent years, fresh fruits and vegetables have been implicated in outbreaks of salmonellosis. Tomatoes were identified as the culprit in 1990 and 1993 and, in 1990 and 1991, cantaloupes were linked to salmonellosis. Investigations of these incidents did not identify the source of contamination. It possibly could have occurred in the fields where the produce was grown, during processing after harvest or during handling in the distribution system.
Person-to-person transmission of salmonella occurs when a carrier's feces, unwashed from his or her hands, contaminates food during preparation or through direct contact with another person. Usually the illness comes from food contaminated with animal feces found on or in raw meats, eggs, fish and shellfish and, most commonly, in poultry. Salmonella also may be found in raw milk or in milk that is contaminated after pasteurization. The bacteria also may be carried by pets birds, fish, dogs, cats and turtles. The U.S. Food and Drug Administration banned the sale of turtles smaller than 4 inches wide in 1975 to prevent the spread of salmonella.
Since early 1950, farmers have administered low doses of penicillin and tetracycline to cows, chickens and pigs to prevent infection and promote growth. As a result, the bacteria in these animals develop a resistance to the drugs. When these drugs are used to treat infections in humans who have eaten meat from treated animals, the drugs are not as effective as they might be. The U.S. Centers for Disease Control and Prevention estimates that between 20 percent and 30 percent of all salmonella cases involve bacteria resistant to antibiotics.
What are the symptoms?
A person may contract salmonellosis many times in his or her life and not always recognize it. Often it is mistaken for the "stomach flu." Symptoms, which last from 24 hours to 12 days, include headache, muscle aches, diarrhea, vomiting, rumblings in the bowels, chills, fever, nausea and dehydration. They usually appear six to 72 hours after ingestion, but carriers have no symptoms. Children younger than 1 year old, people who have had ulcer surgery or take antacids and those whose immune systems have been weakened by other ailments are most susceptible.
Salmonellosis is seldom fatal (the fatality rate is less than 1 percent). Two or three weeks after being infected with salmonella, one in 10,000 cases develops reactive arthritis or Reiter's syndrome as a complication. These patients also may develop an inflammation of the urethra and eyes.
How is salmonellosis treated?
Fluids are recommended to prevent dehydration because the diarrhea that flushes bacteria out of the body drains a great deal of liquid. Pain relievers and fever reducers may make the person more comfortable.
Most cases of salmonellosis are not treated with antibiotics. In fact, antibiotics may prolong the period during which the person can infect others. Also, antibiotics actually may bring on salmonellosis symptoms by upsetting the bacterial balance in the intestines. Antibiotics sometimes are prescribed for infants, the chronically ill and the elderly to prevent salmonella-triggered local infections or bacteremia. Antibiotics also are needed when the bacteria cause meningitis or infections of the blood stream.
Can salmonellosis be prevented?
People are far more likely to contract salmonellosis at home than in a restaurant, so be sure to handle food safely.
Salmonella are killed when food is thoroughly cooked. This means cooking ground beef to at least 155 degrees and making sure all food is cooked properly. Once cooked, any food held in a buffet should be kept hotter than 140 degrees. Cross-contamination--where food is contaminated in the kitchen after it has been cooked--may be avoided by using different utensils, plates, cutting boards and counter tops before and after cooking. Cooked food that stands at room temperature for a long time, especially poultry, is at risk.
Defrost frozen food in the refrigerator or microwave. Refrigerator temperatures should be kept colder than 40 degrees. Rinse poultry in cold water before cooking. Avoid raw milk, raw hamburger meat and raw eggs (many recipes, such as those for homemade ice cream, call for eggs with no subsequent cooking; substitute pasteurized eggs in these recipes). Food contaminated with salmonella may look, smell and taste normal.
Because fruits and vegetables have now been identified as a source of salmonella, it is important that these food items be thoroughly washed in running water before they are eaten.
Wash utensils and wooden cutting boards thoroughly with hot, soapy water. Salmonella may lie dormant for a year or more and then "wake up" when food is present. They also may live in the cut marks on a wooden cutting board. Use an acrylic board that can go in the dishwasher. Rub down or spray wooden boards with a solution of one ounce bleach to one gallon water and allow to air dry. Cutting boards for raw meat and poultry should not be used for cheese, raw vegetables and other foods that will not be cooked before being served.
To prevent the spread of salmonella, wash hands thoroughly after using the bathroom and before handling food. Do not allow an infected person to handle food or work in the kitchen.
Salmonella Nomenclature
The genus Salmonella is a member of the family Enterobacteriaceae, It is composed of bacteria related to each other both phenotypically and genotypically. Salmonella DNA base composition is 50-52 mol% G+C, similar to that of Escherichia, Shigella, and Citrobacter. The bacteria of the genus Salmonella are also related to each other by DNA sequence. The genera with DNA most closely related to Salmonella are Escherichia, Shigella, and Citrobacter. Similar relationships were found by numerical taxonomy and 16S ssRNA analysis.
Salmonella nomenclature has been controversial since the original taxonomy of the genus was not based on DNA relatedness, rather ?names were given according to clinical considerations, e.g., Salmonella typhi, Salmonella cholerae-suis, Salmonella abortus-ovis, and so on. When serological analysis was adopted into the Kauffmann-White scheme in 1946, a Salmonella species was defined ?as "a group of related fermentation phage-type" with the result that each Salmonella serovar was considered as a species. Since the host-specificity suggested by some of these earlier names does not exist (e.g., S. typhi-murium, S. cholerae-suis are in fact ubiquitous), names derived from the geographical origin of the first isolated strain of the newly discovered serovars were next chosen, e.g., S. london, S. panama, S. stanleyville.
Susequently it was found that all Salmonella serovars form a single DNA hybridization group, i.e., a single species composed of seven subspecies, and thenomenclature had to be adapted. To avoid confusion with the familiar names of serovars, the species name Salmonella enterica was proposed with the following names for the subspecies:
enterica ?I
salamae II
arizonae IIIa
diarizonae IIIb
houtenae IV
bongori V
indica VI
Each subspecies contains various serovars defined by a characteristic antigenic formula.
Since this formal Latin nomenclature may not be clearly understood by physicians and epidemiologists, who are the most familiar with the names given to the most common serovars, the common serovars names are kept for subspecies I strains, which represent more than 99.5% of the Salmonella strains isolated from humans and other warm-blooded animals. The vernacular terminology seems preferred in medical practice, e.g., Salmonella ser. Typhimurium (not italicized) or shorter Salmonella (or S.) Typhimurium.
?
You are here: News & Events /
New Salmonella Finding—
Inter-Bacterial Communication!
Salmonella enteritidis.
(K8732-2) Talking bacteria may sound bizarre, but microorganisms do have a primitive form of communication--much as some insects use pheromones to lure a mate or signal an attack. An Agricultural Research Service scientist found this happens with Salmonellabacteria, and her discovery could have big implications for food safety.
Veterinarian Jean Guard-Petter, who is in ARS' Southeast Poultry Research Unit at Athens, Georgia, found that the food pathogen Salmonella enteritidis uses acyl-homoserine lactone, or AHL, as its chemical "call to arms."
"This chemical tells cells to rewrite their genetic programming," says Petter. "It enhances their ability to grow as much as a hundredfold and signals cells to produce molecules that increase virulence—the ability to invade living things and cause disease."
Over the last 15 years, occurrences of S. enteritidis food poisoning have increased fourfold in the United States and fortyfold in Europe.
This large bacterial colony of Salmonella
enteritidis grew rapidly (62 millimeters
in diameter in 16 hours) and readily contaminated eggs when given to chickens
by injection but not when given by mouth.
(K8732-1)
