Digestive System Infections: Microbiology Study Notes

Digestive System Infections

Bacterial Diseases of the Upper Digestive System

The upper digestive system is susceptible to a variety of bacterial infections, many of which are associated with oral health and the stomach. These infections can lead to significant tissue damage and systemic effects if untreated.

• Dental Caries (Cavities): Caused by multiple bacteria, most notably Streptococcus mutans. These bacteria metabolize sugars to produce a slime layer, allowing them to adhere to teeth and form dental plaque. Through lactic acid fermentation, they produce acid that degrades tooth enamel, leading to cavities. Prevention includes regular brushing, flossing, and the use of fluoride, which strengthens enamel against acid attack.

• Periodontal Disease: Encompasses gum disease and gingivitis. Bacterial enzymes degrade gum tissue, causing inflammation and bleeding (gingivitis). Advanced cases may require antibiotics and surgery. Prevention is similar to caries: brushing and flossing.

• Gastritis: Caused by Helicobacter pylori, which produces ammonia to neutralize stomach acid and degrades the protective mucous lining. This allows acid to damage the stomach wall, leading to ulcers. Treatment includes antibiotics and acid-inhibiting drugs.

Viral Diseases of the Upper Digestive System

• Oral Herpes Simplex: Caused by Herpes Simplex Virus-I (HSV-1), which establishes latent infections. Most cases are asymptomatic, but about one-third of infected individuals experience recurrent cold sores. The virus can also infect other body parts (e.g., herpetic whitlow on fingers). Treated with topical acyclovir, which is effective only on active lesions.

• Mumps: Caused by the Mumps virus and transmitted via infectious droplets. Symptoms include fever, loss of appetite, headache, and swelling of the salivary glands. Complications are more severe in adults, including reproductive organ inflammation and increased miscarriage risk. Prevention is through the live attenuated MMRV vaccine; no treatment is available.

Bacterial Diseases of the Lower Digestive System

Infections of the lower digestive tract often result in gastroenteritis, characterized by inflammation, abdominal cramps, nausea, vomiting, and diarrhea. Severe cases may involve dysentery (bloody diarrhea) or intoxication from preformed toxins.

• Cholera: Caused by Vibrio cholerae, which produces an enterotoxin that induces massive electrolyte and water loss from the intestines, leading to severe dehydration and potentially death. Treatment is primarily rehydration therapy; prevention relies on clean water and sanitation.

• Shigellosis: Caused by Shigella species, closely related to E. coli. Transmitted via contaminated food and water, Shigella invades intestinal cells, causing inflammation and dysentery. Some strains produce Shiga toxin, which can lead to hemolytic uremic syndrome. Treatment includes antibiotics and rehydration; prevention is through sanitation.

• E. coli Gastroenteritis: Most E. coli strains are harmless, but pathogenic strains possess virulence factors. ETEC (Enterotoxigenic E. coli) produces a cholera-like toxin causing watery diarrhea, while EHEC (Enterohemorrhagic E. coli, e.g., O157:H7) produces Shiga toxins, leading to bloody diarrhea and kidney complications. Treatment is supportive; antibiotic resistance is a concern.

• Salmonellosis: Non-typhoidal Salmonella is transmitted via animal feces-contaminated food, causing gastroenteritis. Typhoid fever, caused by Salmonella typhi, is more severe and systemic. Treatment for non-typhoidal cases is rehydration; typhoid fever requires antibiotics.

• Clostridium difficile Infection: Often associated with antibiotic use, C. difficile colonizes the large intestine, causing antibiotic-associated diarrhea and pseudomembranous colitis. Treatment includes antibiotics, probiotics, and fecal transplants, which restore normal microbiota.

Viral Diseases of the Lower Digestive System

• Viral Gastroenteritis: Caused by enteroviruses such as Rotavirus and Norwalk virus. Symptoms include fever, diarrhea, and vomiting. Transmission is fecal-oral, and outbreaks are common. Treatment is supportive; vaccines are available for some viruses.

Viral Diseases of the Liver

• Hepatitis A: Transmitted via the fecal-oral route, causing acute, self-limiting liver inflammation. Symptoms include malaise, diarrhea, nausea, liver damage, and jaundice. Prevention includes vaccination and passive immunity post-exposure.

• Hepatitis B: Transmitted through bodily fluids, can cause acute or chronic infection, cirrhosis, and liver cancer. Prevention is via subunit vaccine; treatment involves antivirals to slow disease progression.

• Hepatitis C: Spread by contaminated needles and fomites, often leads to chronic infection, cirrhosis, and liver cancer. No vaccine is available, but combination antiviral therapy can cure the infection.

Protozoan Diseases of the Digestive System

• Giardiasis: Caused by Giardia lamblia, transmitted via contaminated water. Symptoms include indigestion, nausea, flatulence, and explosive diarrhea. Treated with metronidazole.

• Cryptosporidiosis: Caused by Cryptosporidium, transmitted by improperly treated water and resistant to chlorine. Symptoms include fever, nausea, cramps, and watery diarrhea. Can be fatal in immunocompromised individuals; removed by ozone or UV treatment.