The digestive system consists of the gastrointestinal tract, which includes the oral cavity, pharynx, esophagus, stomach, and intestines, and a number of associated structures and glands such as the teeth, salivary glands, liver, and pancreas. These organs consume food, digest it, absorb nutrients, and eliminate waste that is not absorbed.
Dental caries. Dental caries, or cavities, is a universal microbiological problem. Most cases are caused by Streptococcus mutans, which adheres to the tooth enamel and produces glucans, which are a meshwork of glucose molecules. Together with bacteria and debris, glucans make up the dental plaque. The bacteria ferment carbohydrates in the diet and produce lactic acid, acetic acid, butyric acid, and other acids that damage the enamel. The susceptibility to tooth decay can be lessened by thorough brushing and flossing to remove S. mutans and by reducing the consumption of sugar.
Periodontal disease. Periodontal disease involves damage to the tissues surrounding and supporting the teeth. The gingiva, or gums, are also involved, as is the bony socket in which the tooth is embedded. Among the many causes of periodontal disease is Bacteroides gingivalis, an anaerobic, Gram‐negative rod. Spirochetes such as species of Treponema also play a role.
Shigellosis. Shigellosis is also known as bacillary dysentery. It is caused by four species of the Gram‐negative rod Shigella: S. dysenteriae, S. boydii, S. sonnei, and S. flexneri. Most cases occur in young children, and transmission takes place by an oral‐fecal route. The disease is highly communicable and is initiated by a low number of bacteria as compared to other infections. The bacteria produce a powerful toxin (the shigalike toxin) that causes lesions and inflammation of the intestinal lining and stools streaked with blood and mucus. Dehydration is a threat, and rehydration is necessary to prevent death. Antimicrobial therapy is also available with a number of antibiotics, including quinolones.
Salmonellosis. Salmonellosis refers to a number of foodborne and waterborne infections due to species of Salmonella. The organisms are Gram‐negative rods and include, S. enteritidis and S. choleraesuis. They are transmitted by a fecal‐oral route, and patients experience extensive diarrhea with fever, abdominal cramps, and nausea. The infection usually limits itself, and antibiotic therapy is not used unless severe complications exist. Chicken, egg, and poultry products are often involved because Salmonella strains live in domestic fowl.
Typhoid fever. Typhoid fever is caused by the Gram‐negative, aerobic rod Salmonella typhi. The disease is transmitted by contaminated food and water and begins with a high fever lasting several days or weeks. A skin rash called rose spots is associated with the disease. Patients are tired, confused, and delirious, and the mortality rate without antibiotic therapy is high. Intestinal bleeding and wall perforation may occur. Chloramphenicol is used in therapy. The carrier state exists in people who have recovered. These people shed the bacteria in their feces and are a source of infection to other individuals.
Cholera. Cholera, caused by Vibrio cholerae, is a disease transmitted primarily by contaminated water. The etiologic agent is a short, curved, Gram‐negative rod having a single polar flagellum. Its exotoxin binds to host cells, and the host epithelial cells secrete large quantities of chloride into the intestinal lumen followed by large amounts of water and sodium and other electrolytes. Massive diarrhea accompanies the disease, and dehydration often leads to death. The only effective treatment is rehydration accomplished by intravenous and oral rehydrating solutions.
Escherichia coli infections. Escherichia coli is the Gram‐negative rod routinely used in research and industrial microbiology because it is generally harmless. However, certain strains produce toxins or have the capability of invading tissue, and these strains can cause infections in humans. One disease attributed to E. coli is traveler's diarrhea, an infection developing in travelers to Caribbean and Central American countries, among others. Infant diarrhea and urinary tract infections are also caused by E. coli. E. coli 0157:H7 has been implicated in recent years in numerous foodborne outbreaks. Patients suffer hemorrhaging, especially in the kidneys, and infections can be serious.
Campylobacteriosis. Campylobacteriosis is caused by Campylobacter jejuni, a curved, Gram‐negative rod often transmitted by contaminated milk. Patients experience bloody diarrhea, as well as abdominal pain and fever. Most infections limit themselves, but antibiotic therapy with erythromycin hastens recovery.
Gastric ulcers disease. In recent years, gastric ulcers have been related to the Gram‐negative rod Helicobacter pylori. This organism survives in the lining of the stomach by producing enzymes to convert urea to ammonia, thereby raising the pH. Penetration of the stomach wall's mucosa follows. Antibiotics such as tetracycline have been used to limit the bacterium's proliferation.
Staphylococcal food poisoning. Staphylococcal food poisoning is the most frequently reported type of food poisoning in the United States. It is caused by toxin‐producing strains of Staphylococcusaureus. The toxin, an enterotoxin, is produced in food and affects the gastrointestinal tract causing vomiting, diarrhea, and abdominal cramps. The incubation period is a short few hours, and the illness limits itself after a brief but intense period. Antibiotic therapy is not used. Fluid replacement may be necessary if severe diarrhea has taken place. Careful handling of foods, especially leftover foods, is paramount in preventing this disease.
Clostridial food poisoning. Clostridial food poisoning is due to Clostridium perfringens, a sporeforming, anaerobic rod. This organism produces its toxin in meat, and consumption of contaminated meat leads to mild gastroenteritis, with diarrhea. The infection is self‐limiting and rarely requires antibiotic therapy. Clostridium botulinum also is transmitted in contaminated food. Its toxin affects the nervous system.
Leptospirosis. Leptospirosis is a disease of animals (such as dogs) as well as humans, where it causes damage to the liver and kidney. The etiologic agent is Leptospira interrogans, a spirochete. Humans usually become infected by contact with urine of the animals as the spirochete enters abrasions in the skin. Patients suffer muscle aches, fever, and infection of the liver. Kidney failure may also occur. Penicillin antibiotics are used for therapy.
Other bacterial diseases. A mild form of gastrointestinal illness is caused by Vibrio parahaemolyticus. This Gram‐negative, curved rod often contaminates fish, and the diarrhea it causes may be mild or explosive. Low‐grade fever, cramps, and vomiting accompany the illness. The organism lives in salt‐water environments, especially in the region near Japan.
A type of colitis is caused by Yersinia enterocolitica, a Gram‐negative rod that displays bipolar staining. This organism adheres to the epithelium of the intestine and produces an enterotoxin. Intense abdominal pain accompanies the infection. The organism is associated with leftover foods, especially those held in the refrigerator. Milk and animal products transmit the bacteria to humans.
A type of food poisoning is caused by Bacillus cereus, an aerobic, sporeforming rod. This organism's spores often survive the cooking process, and its toxins accumulate in vegetable and rice dishes. The infection is accompanied by vomiting or diarrhea or both.