Salmonella is rod shaped gram negative bacteria non spore forming motile entro-bacteria. The length is 2 to 5µm and diameter is .7 to 1.5µm. Mobility is due flagella. Salmonella belongs to
- kingdom Bacteria
- Phylum Proteobacteria
- Class Gamma probacteria
- order Entrobacteria
- family Entrobacteria
- Genus Salmonella.
Most Common Salmonella Strains
Ten most frequently isolated Salmonella strains causing human disease are as follows;
- S enteritidis (26.1%)
- S typhimurium (22.1%
- S enteritidis heidelberg (4.8%)
- Salmonella enteritidis newport (4.3%)
- SALMONELLA hadar (2.7%)
- Salmonella enteritidis agona (2.0%)
- SALMONELLA enteritidismontevideo (1.7%)
- Salmonella oranienburg (1.6%)
- Salmonella muenchen (1.5%)
- Salmonella enteritidis thompson (1.5%)
Diseases Caused by Salmonella
Salmonella like Escherichia Coli is widely spread in the environment .The major disease which is caused by Salmonella are as follows:-
- Typhoid fever
- Paratyphoid fever
- Food borne illness.
Salmonella causes zoonotic infection which can spread between human to human. The individuals are mostly infected by consuming contaminated food. The virulence of organism is dependent on the specificity of the antigen present on the capsules of the organism. The common type of Salmonella present in human are Typhoid, Paratyphoid, it does not occur in the other animals where as Salmonella Entrica and subEntrica Serovar is the main causative agent in animals.
Pathogenesis of Salmonella
When living salmonella reaches the gastrointestinal tract some of the micro organism are killed in the stomach, surviving Salmonella enter the small intestine and multiply in the tissue. By the end of the incubation period the microorganism is poisoned from the endotoxin released by the dead salmonella results in the local response to endotoxin causing enteritis and gastrointestinal disorder in the generalized form of the disease, the endotoxin through lymphatic enter the blood and various organ of the body like liver, spleen, kidney, forms as (septic foci).The endotoxin first effect the vascular and nervous system, In vascular system infection/endotoxin increases permeability and decreased the tone of the vessels and upset thermal regulatory system. Vomiting and Diarrhoea are major symptoms water and electrolytes are lost from the body.
Sources of Salmonella Infection
- Infected food often gaining unusual look or smell
- Poor Kitchen Hygiene can lead to outbreak
- Excretion from sick infected ,but apparently appears clinically healthy people and animals (especially endangers the animal and caregivers)
- Polluted surface water
- un hygienically thawed fowl(melted water contains many bacteria)
- An association with reptile (Pet tortoise ,snakes, turtle, also frogs may developed disease from salmonella)
Salmonella bacteria can sometimes survive without a host in water that is contaminated from excreta of carrier animals.
Mode of Transmission of Salmonella:
In Human Salmonella infection is transmitted directly, when individuals consumed contaminated foods of animal origin such as meat or eggs. One can get indirectly infected by ingesting organisms present in raw vegetable fruits and water. Animals like reptiles, chicks, ducklings, Livestock, dogs, cats, adult poultry cage birds can also be a source of transmitting infection directly.
Animal Transmission of Salmonella infection
Salmonella spp. is mainly transmitted by the fecal-oral route. They are carried asymptomatically in the intestines or gall bladder of many animals, and are continuously or intermittently shed in the feces. Vertical transmission occurs in birds, with contamination of the vitelline membrane, albumen and the yolk of eggs. Salmonella spp. can also be transmitted in utero in mammals. Animals may also become infected from contaminated feed (including pastures), drinking water, or close contact with infected animal (including humans). Birds and rodents can spread Salmonella to livestock. Carnivores are also infected through meat, eggs, and other animal products that are not thoroughly cooked
Disease in Human
In humans, salmonellosis varies from a self-limiting gastroenteritis to septicemia. Whether the organism remains in the intestine or disseminates depends on host factors as well as the virulence of the strain.
Incubation Period of Salmonella Infection
Incubation Period for Gastroenteritis Disease is: 12 hrs to 3 days and for Enteric fever: 10 to 14 days respectively. The major difference between Salmonella Typhi and Salmonella Typhimurium is, in Salmonella Typhi is adapted to the host systemic infection resulting in Enteric fever with little diarrhoea ,vaccine are available may be used as preventive measure ,where as carrier exist for longer duration .In Salmonella Typhimurium It is non host ,It is rarely Extra intestinal but usually causes diarrhoea ,no vaccine is available and no long term carrier exist.
Asymptomatic infections can also be seen all serovars can produce all forms of salmonellosis, although a given serotype is often associated with a specific syndrome (e.g. Salmonella choleraesuis tends to cause septicemia). Salmonellosis acquired from reptiles is often severe, and may be fatal due to septicemia or meningitis. Most cases of reptile-associated salmonellosis are seen in children under 10 and people who are immunocompromised.
Clinical Symptoms of Salmonella
- Clinical Symptoms are Enteric fevers that are the severe form of systemic salmonellosis. Although most cases are caused by S. typhi, a human pathogen, other species can also cause this syndrome.
- Gastrointestinal disease may be the first sign, but it usually resolves before the systemic signs appear.
- The symptoms of enteric fever are non-specific and may include fever, anorexia, headache, lethargy, myalgias and constipation. This disease can be fatal, due to meningitis or septicemia, if not treated quickly.
Complications of Salmonella Infection
- Cardiovascular – Endocarditis, pericarditis, valve perforation, and arteritis
- CNS – Meningitis, ventriculitis, and abscess
- Pulmonary – Pneumonia, abscess, empyema, and bronchopleural fistula
- Bone/joints – Osteomyelitis and septic arthritis
- Hepatobiliary – Hepatic abscess, cholecystitis, and peritonitis
- Splenic – Abscess
- Urinary -Cystitis, pyelonephritis, and renal abscess
- Genital – Ovarian abscess, testicular abscess, prostatitis, and epididymitis
- Soft tissue – Abscess.
Diagnosis of Salmonella Infection
Confirmation of Salmonellosis can be done by isolating the organisms from feces. . Salmonella can be isolated from blood and grown on a wide variety of selective and non-selective media. Enrichment broths can increase the probability of isolating the organism. Salmonella spp. is identified with biochemical tests and the serovar can be identified using serology for the somatic (O), flagellar (H) and capsular (Vi) antigens. PCR and other genetic techniques may also be available.
Treatment and Management of Salmonella Infection
Salmonella management can be divided into Patient Education and prevention, Medicalcare and Surgical Care. When the patient reports in the emergency with history of loose motion and diarrhoea then signs of Dehydration presist, immediate hydration should be done, and tests samplkng including blood for labs, and stool for culture shall be taken. Maintain vital signs. If there is indication of blood transfusion, then Transfusions should be based on hemoglobin and hematocrit levels. The main purpose is correction of electorylte imbalances and control of pain, nausea, vomiting, and diarrhoea is mandatory.
- If the patient comes with the History of Gastroenteritis: usually a self-limiting disease, Fluid and electrolyte replacement can be done. Antibiotics is recommended to reduce the duration of symptoms (-), and conditions in Newborns and older than 50 years having severe atherosclerosis, immunosuppressed, Cardiovascular abnormalities, Prostheses. The treatment duration is usually 48-72 hours.
- Enteric (i.e. typhoid) fever is best treated with antibiotics for 10-14 days. Prolonged bacteremia and focal infection are treated with maximal doses of antibiotics for 4-6 weeks, Search for the source, which may require surgical intervention. Oral quinolone, trimethoprim-sulfamethoxazole, or amoxicillin for 48-72 hours are recommended antibiotics . Chloramphenicol may be used in resistance cases of Typhoid fever; high doses of chloramphenicol may cause bone marrow suppression. Alternatively, use of an intravenous antibiotic, such as ceftriaxone, is effective in patients who cannot tolerate oral medications.
- Surgical Treatment. Typhoid fever may occasionally be complicated by intestinal perforation or hemorrhage, cholecystitis, Endocarditis, arteritis, Osteomyelitis, or soft tissue abscess formation, Long-term carrier with S typhi (usually with the gallbladder as the reservoir) may necessitate cholecystectomy.
Sources of Salmonella Infection
Salmonella bacteria live in the intestine of the people, animals and birds.
- The Common foods which are contaminated are raw meat, poultry, and seafood. Feces may lodge or may get on to raw meat and poultry during the process. Sea food may get contaminated if harvested in polluted water.
- Some chicken produces eggs that contain salmonella before shell is produced
- Fruits and vegetable when washed with contaminated water may result in infection
- Cooked food may get contaminated with juices of meat and salad.
- The people who do not wash their hand thoroughly after toilet or changing diaper they are more prone to get Infection and can also be transmitted through them
- Animals like birds and reptiles can be a source of infection.
- Food Handlers who returns to work before they are recovered from the infection completely are likely to spread the disease further
- The individuals who are infected for a longer duration may become chronic carrier and excrete salmonella in their feces.
Prevention of Salmonella Infection
Individuals who are suffering from Salmonella infection, preventive measures may be suggested as.
- Washing of Hands: Wash your hand after going to toilet, liquid soap or any other soap may be used for that purpose. If you are suffering from infection do not prepare or serve the food. If cloth or bedding is soiled first remove stool and then disinfect the bedding.
- Regularly clean the toilet with disinfectant.
- stay off the work/school for at least for 48 hours.
- If you are working in food industry and developed vomiting and Diarrhoea, you must inform your employer and keep away from work for at least for 48 hours.
- Make sure you cook the food thoroughly especially meat.
- Wash raw fruits and vegetable before you eat.
- Drink pasteurized milk or avoids eggs.
- Chilling: Food need to be chilled or refrigerated .If the food is left out from the fridge; bacteria may multiply and cause food poisoning. Temperature of Fridge must be kept between 0o c and 5o C and do not leave the fridge unnecessary open.
- Wash your hand after touching the raw food.
- Separate raw and cooked food.
- Keep the raw meat in a sealable container at the bottom of the fridge.
- Do not use the same surface or chopping board for preparing raw and ready to eat foods.
- Make sure that knives and utensils are cleaned after preparing the raw food.
Prognosis of Salmonella Infection
In pre antibiotic the era mortality rate due salmonella infection was 15% .Where as in the developing countries the morality due to salmonella infection has even exceeded to 30 %.The patients who are appropriately treated the rate of salmonella has even reduced to 1%.
History of Salmonella
- In 1885 it was first isolated by Theobald Smith. S. Choleraesuis from porcine intestine around. He worked for Daniel Salmon, who had nothing to do with the work.
- 1829- P.Ch.A. Louis in Paris separated typhoid from other fevers.
- 1884-Gaffkey Germany isolated Salmonella Typhi from spleens of infected patients
- 1896- first heat killed vaccine by Pfeiffer and Kalle.
- 1920 to 1940-Kaufman and White developed the serotype classification of Salmonella
- 1952-Zinder and Lederberg-discovered genetic transduction using phage P22. 1973-Bruce Ames developed the “Ames Test” to determine mutagenic activity of chemicals.
- 1900- The genus Salmonella was finally formal adopted by J.ligniceres