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The important type of bacterial food infections are as follows:
1. Food Borne Gastroenteritis by Salmonella spp.-Salmonellosis:
Salmonellosis may result due to the ingestion of the food material contaminated with Samonella spp. especially Salmonella typhi and Salmonella enteritids. Salmonella is a gram-negative, non-sporulating, facultive anaerobic, rod that ferments glucose with acids and gas but not with sucrose or lactose.
The organism arises from cats, dogs, swine and cattle but more important sources are poultry and eggs. The common disease is called gastroenteritis, which is caused by ingestion of contaminated food such as meat, poultry, egg, etc. The most important vectors for salmonella infection are flies that spread the disease from contaminated fecal material to food.
The major types of food items involved in this infection are meat products, hash, sausages, cured meats (ham, bacon, tongue, etc.), sandwiches and chili. Milk and milk product including fresh milk, fermented milk, ice cream and cheeses are also involved in salmonella infection.
The major types of salmonella infection in humans are:
(i) Thyphoid fever (Enteric fever)
(ii) Organism – Salmonella typhi; reason – enterotoxin/ cytotoxin.
(iii) Parathyphoid (Enteric fever)
(iv) Organism – Salmonella paratyphi A, B, C
The symptoms occur after an incubation time of 8 hours due to enterotoxin/cytotoxin production. The symptoms of salmonella gastrointestinal infections are diarrhea, fever, chills, abdominal pain, vomiting, dehydration, headache, malaise, etc. Other symptoms are watery, greenish foul smelling stool, prostration, muscular weakness, faintness, restlessness, twitching and drowsiness. Usually symptoms persist for 2 to 3 days followed by uncompleted recovery.
The main preventive measures of salmonella infections are:
(a) Avoidance of contamination of food with Salmonella from different sources
(b) Destruction of the organisms in food by heating or any other method
(c) Prevention of growth of the organism in foods by proper refrigeration or similar methods
2. Food Borne Gastroenteritis by Shigella spp.-Shigellosis (Bacillary Dysentery):
Shigella is a gram-negative, non sporulating, facultative anaerobic, rod shaped organism responsible for bacillary dysentery in human. Different species of these organisms are Shigella flexneri, Shigella dysenteriae, Shigella sonnei and Shigella boydii. The pathogenicity of the organism involves the release of a lippopolysacchride endotoxin which affects the intestinal mucosa. Incubation time is 1-7 days, usually less than 4 days. The symptoms are- abdominal cramp, fever, chills, diarrhea, watery stools containing blood, headache, dehydration, nausea, etc.
The transmission of the diseases is via the fecal-oral route. The usual mode of transmission is directly person-to-person hand-to-mouth, in the setting of poor hygiene among children. Infections are associated mucosal ulceration, rectal bleeding, drastic dehydration; fatality may be as high as 10-15% with some strains. Reiter’s disease and hemolytic uremic syndrome are possible diseases that have been reported in the aftermath of shigellosis.
Shigella can be transmitted through food. Food known to do so includes salads (potato, tuna, shrimp, macaroni and chicken), raw vegetables, milk and dairy products and meat. Contamination of these foods is usually through the fecal-oral route. Fecally contaminated water and unsanitary handling by food handlers are the most common causes of contamination.
Simple precautions can be taken to prevent getting shigellosis. Wash hands before handling food and thoroughly cook all food before eating. Treatment consists mainly of replacing fluids and salts lost because of diarrhea. Antibiotics such as trimethoprim- sulfamethoxazole, norfloxacin, ciprofloxacin or furazolidone may be used as the drug of choices. Antidiarrheal drugs such as diphenoxylate or loperamide are also used against bacillary dysentery.
3. Food Borne Gastroenteritis by Listeria spp.-Listeriosis:
Listeria monocytogenes is a gram-positive, motile, rod shaped bacteria causing the disease called listeriosis. It is mainly infected in cattle and produces abortion and mastitis. The other organisms are sheep and chicken. This organism is mainly present in water, milk, silage, sewage and the feces of human and animals. In human it is mainly infected in pregnant women, new born, fetus and immuno compromised people.
The symptom of listeriosis usually lasts for 7-10 days. The most common symptoms are fever and muscle aches and vomiting. Nausea and diarrhea are less common symptoms. If the infection spreads to the nervous system it can cause meningitis, an infection of the covering of the brain and spinal cord. Symptoms of meningitis are headache, stiff neck, confusion, loss of balance and convulsions.
There are four distinct clinical syndromes:
i. Infection in Pregnancy:
Listeria can proliferate asymptomatically in the vagina and uterus. If the mother becomes symptomatic, it is usually in the third trimester. Symptoms include fever, myalgias, arthralgias and headache. Miscarriage, stillbirth and preterm labor are complications of this infection. Symptoms last 7-10 days.
ii. Neonatal infection:
There are two forms – One, an early-onset sepsis, with Listeria acquired in utero, results in premature birth. Listeria can be isolated in the placenta, blood, meconium, nose, ears and throat. Late-onset meningitis is acquired through vaginal transmission, although it also has been reported with caesarean deliveries.
iii. Central Nervous System Infection:
Listeria has a predilection for the brain parenchyma, especially the brain stem and the meninges. It can cause cranial nerve palsies, encephalitis, meningitis, meningoencephalitis and abscesses. Mental status changes are common. Seizures occur in at least 25% of patients.
iv. Gastroenteritis:
L. monocytogenes can produce food-borne diarrheal disease, which typically is noninvasive. The incubation period is 21 days, with diarrhea lasting anywhere from 1-3 days. Patients show the symptoms such as fever, muscle aches, gastrointestinal nausea or diarrhea, headache, stiff neck, confusion, loss of balance or convulsions.
Listeria monocytogenes is ubiquitous in the environment. The main route of acquisition of Listeria is through the ingestion of contaminated food products. Listeria has been isolated from raw meat, dairy products, vegetables, seafood, soft cheeses and unpasteurized milk.
The main means of prevention is through the promotion of safe handling, cooking and consumption of food. This includes washing raw vegetables and cooking raw food thoroughly, as well as reheating leftover or ready-to-eat foods like hot dogs until steaming hot.
4. Food Borne Gastroenteritis by Staphlococcus spp. Staphylococcal Enterotoxicosis (Staphylococcus Food Intoxication):
Staphylococcus intoxication caused by Staphylococcus aureus, one of the most common food poisoning is caused by the ingestion of the enterotoxin formed in the food. The toxin is produced inside the organism and it causes gastroenteritis or inflammation of the intestinal tract.
Staphylococcus aureus is gram-positive, facultative anaerobic cocci occurs as grape like clusters. Most of the staphlococcal strain from pyogenic lesion produces golden yellow colonies and strain from normal skin produces white colored colonies on solid media.
The toxigenic cocci are very salt and sugar tolerant and the cultures are coagulase positive.Most of the organisms are fermentative and proteolytic but they will not produce offensive odour in the food. Staphylococcus aureus produces six different types of enterotoxins, toxin A, B, C1, C2, D and E. Most of the food poisoning is due to type A. There are some reports indicated the role of type D toxin in food poisoning.
The enterotoxins are simple proteins with molecular weight between 26,000 and 30,000. The long, single polypeptide chain is cross linked with disulfide linkage to form a special cystine loop. This toxin is produced best at 40°C and it may evident within 4 to 6 hrs.
The toxin is thermal stable especially type B toxin hence heat treatments of pasteurization (72°C for 15 Sec) and ultra-high temperature (143.3°C for 9 Sec) heating would not sufficient to inactivate the enterotoxins.
So many types of foods are involved in staphylococcal food poisoning, custard and cream rich bakery products, ham and poultry may cause high outbreak. Other food items include meat and meat products, fish and fish products, milk and milk products, salads and salad dressings, puddings and cream sauces.
The most important conditions for an outbreak of staphylococcus food poisoning are:
(1) The food must consists of enterotoxin producing Satphylococci,
(2) The food must act as good substrate which consists necessary nutrients for the growth of Staphylococcus,
(3) Favorable temperature for the growth and,
(4) The enterotoxin rich food must be ingested.
The most important symptoms of this infection in human are salvation, nausea, vomiting, retching, abdominal cramp, headache, muscular cramping, sweating, chills, prostration, weak pulse, shock and shallow respiration.
The diagnosis of staphylococcal gastroenteritis would be depended on the isolation of staphylococci, characterization and demonstration that these organism produce enterotoxin or isolation and detection of enterotoxin. The best method for prevention of this type of food intoxication includes prevention of contamination of the food with staphylococci, prevention of the growth of the staphylococci and killing staphylococci in foods. Growth of staphylococci can be arrested by adequate refrigeration, pasteurization of milk, addition of bacteriostatic agents such as antibiotics and good sanitation.
5. Food Borne Gastroenteritis by Clostridium spp.:
Clostridium is a gram-positive, spore forming, motile, rod shaped, hyperthermophilic, saprophytic, gas producing and obligate anaerobic bacteria commonly found in soil and meat products. Most of the species are hemolytic on blood agar. Saccharolytic species turn the meat pink and proteolytic species produce black spots on meat and produce foul, pervasive and offensive odour.
Some of the species would be grown above 100°C and spores are resistant to aminoglycosides, quinolones and phenolic disinfects. The most important species responsible for food borne gastroenteritis are C. botulinum and C. perfringens.
Botulism is a food borne intoxication caused by ingestion of food containing neurotoxins produced by Clostridium botulinum. Based on the serological specificity of the toxin these are classified in to seven groups namely type A, B, C, D, E, F and G. Type A and E are the most powerful toxins infected human.
Based on the toxin type, cultural and physiological characters Clostridium botulinum strains are divided into three. Group I, produces type A toxin and these are proteolytic. Group II, toxin types are E, B and F and these are non proteolytic and Group III, includes non proteolytic type C and D.
The toxin production mainly based on several factors such as spore germination, growth, nutritive properties, moisture content, redox potential, pH, salt concentration and time of storage of food. The toxin is a protein and so powerful. It is absorbed mostly in the small intestine and paralyzes the involuntary muscle of the body.
The toxin is a two-chain polypeptide with a 100-kDa heavy chain joined by a disulphide bond to a 50-kDa light chain. Heat treatment at 80°C for 5 to 6 minute would inactivate type A toxin while at 90°C for 15 minute is required for toxin type B. The most important food item involved in this diseases are beans, sweet corn, beets, asparagus, spinach, chard, tomatoes, apricots, peaches, meat and poultry products.
The conditions favored for the outbreak of the diseases are:
(1) Presence of any type of C. botulinum spores in food,
(2) Survival of spores due to inadequate food processing steps,
(3) Favorable environmental conditions for spore germination and toxin production,
(4) Improper cooking of food and,
(5) Ingestion of the toxin-bearing food.
The symptoms of the diseases will appear with 12 to 36 hr. The symptoms include acute digestive disturbance, fatigue, dizziness, vomiting, fever, chills, diarrhea, headache, nausea and later lead to constipation. Symptoms are similar for type A, B and E poisoning but nausea, vomiting and urinary retention are more common in type E poisoning.
The best and well-practiced method of treatment of botulism is the administration of antitoxin. Other methods are also in use, artificial respiration, keeping patient quiet and maintaining fluid balance in the body. The methods to prevent the outbreak of botulism include use of approved heat treatment for canned food, rejection of swollen or other spoiled foods, boiling of a suspected food for at least 15 minutes, maintaining good sanitation during the production, processing and handling and use of packaged food.
Clostridium Perfringens Gastroenteritis:
The food-poisoning strains of C. perfringens exist in soils, water, foods, dust, spices and the intestinal tract of humans and other animals. C. perfringens is mesophilic, with an optimum temperature between 37°C and 45°C. The lowest temperature for growth is around 20°C and the highest is around 50°C.
The causative factor of C. perfringens food poisoning is an enterotoxin. The various types of CPE enterotoxins are alpha, beta, delta and epsilon. It is a spore-specific protein; its production occurs together with that of sporulation. All known food poisoning cases by this organism are caused by type A strains.
The CPE protein contains 319 amino acids and it binds to either claudin or a 50 kDa eukaryotic membrane receptor that leads to the formation of a 90-kDa CPE-containing complex in host cell membranes. A larger complex is formed by the addition of host cell membrane proteins that ultimately leads to the induction of permeability changes in cell membranes and death of host cells.
Symptoms appear between 6 and 24 hours, especially between 8 and 12 hours, after the ingestion of contaminated foods. The symptoms are characterized by acute abdominal pain and diarrhea; nausea, fever and vomiting are rare. The fatality rate is quite low and no immunity seems to occur although circulating antibodies to the enterotoxin may be found in some persons with a history of the syndrome.
The main food items are involved in this food poisoning are frozen foods, fruits and vegetables, home-prepared foods and mostly for raw meat, poultry and fish.
The most important preventive measures are cook meat and poultry until the internal temperature reaches 75°C, thoroughly wash and sanitize all containers and equipment that previously had contact with raw turkey, wash hands and use disposable plastic gloves when deboning, deicing, or handling cooked meat and meat products, chill meat and poultry stock as rapidly as possible after cooking, use shallow pans for storing stock and deboned turkey in refrigerators, bring stock to a rolling boil before making gravy or dressing and just prior to serving, meat pieces submerged in gravy until largest portions of meat reach 165°F.
6. Food Borne Gastroenteritis by Vibrio app.:
Vibros are gram-negative, rigid, curved road that are actively motile by means of a polar flagellum. Vibrios are mainly present in marine environment but it is one of the important food contaminant. It is strongly aerobic and it grows within temperature ranges of 16-40°C. On simple solid media colonies are moist, translucent, round disc and it fermented lactose. The important species of Vibrio responsible for food borne gastroenteritis is Vibrio parahaemolyticus.
Vibrio parahaemolyticus is a curved, rod-shaped, gram-negative bacterium found in brackish saltwater, which, when ingested, causes gastrointestinal illness in humans. V. parahaemolyticus is oxidase positive, motile, facultatively aerobic and does not form spores. It is a halophile (require 1 to 3 % NaCl) and optimum temperature for growth is 35 to 37°C. The main food items involved in diseases are sea foods, oysters, shrimps, fishes, shellfish and crustacean.
The main virulent factors of this disease are two pathogenicity islands (PAI). Each pathogenicity island contains a genetically- distinct type III secretion system, which is capable of injecting virulence proteins into host cells to cause disease. Additionally, two well-characterized virulence proteins are typically found in the pathogenicity islands, the thermostable direct hemolysin gene (TDH) or the TDH-related hemolysin gene (TDH). Strains possessing the hemolysins exhibit beta-hemolysis on blood agar plates. The incubation period of the disease is 2-48 hr, generally 12 hr. The most important symptoms are abdominal pain, diarrhea, nausea, vomiting, mild fever, chills, headache and prostration.
The main preventive measures include cook foods properly, chills foods rapidly in small quantities, prevent cross contamination from saltwater fish, sanitize equipment, avoid using sea water for rinsing foods to be eaten raw or for cleaning.
7. Food Borne Gastroenteritis by Yersinia spp.-Yersiniosis:
Yersinia is a gram-negative, non sporulating, rod shaped, facultative anaerobic enterobacteriaceae member associated with plague or Yersiniosis in human. The main species is Yersinia enterocolitica. It has been isolated from the intestinal tracts and feces of many animals including cats, dogs, deer, raccoons and horses.
Yersinia enterocolitica has been isolated from many food items such as beef, pork, liquid egg, soft cheese, raw and pasteurized milk, fish, shrimps, crab, turkey and raw oytsers. The incubation time is 24-36 hours. The symptoms include abdominal pain, fever, chills, diarrhea, malaise, headache, dehydration, vomiting, nausea, etc.
The abdominal discomfort is specific and manifest as a sharp pain in the lower right quadrant of the abdomen. Hence, it is termed as pseudoappendicitis. Also Yersinia is implicated as one of the causes of reactive arthritis, an autoimmune condition that develops in response to an infection in another part of the body.
8. Food Borne Gastroenteritis by Campylobacter spp. – Campylobacteriosis:
Campylobacter is a gram-negative, rod-shaped, non-spore forming, microaerophilic, spirochete commonly found in animal feces. It is one of the most common causes of human gastroenteritis in the world. The most important organisms are heat tolerant species, Campylobacter jejuni and Campylobacter coli associated with acute gastrointestinal diseases in human.
Campylobacter jejuni is associated with warm blooded animals, or their products. Numbers of different strains have been isolated from chicken carcasses and feces, swine carcasses and feces, sheep carcasses and feces, turkey and pork, red and ground beef. This pathogen is transmitted by poorly cooked poultry, milk, pork products.
The incubation period is 2-10 days. Most of the strain produces powerful enterotoxin and the toxin is heat liable, so proper cooking of food can prevent its transmission. Symptoms of campylobacteriosis include abdominal pain and cramps, diarrhea, headache, fever and bloody stool.