Enteric Infections and Food Poisoning

Gastrointestinal Tract Defenses and Normal Biota

  • The gastrointestinal (GI) tract is a long tube from the mouth to the anus.
  • It consists of eight main sections: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus.
  • Four accessory organs: salivary glands, liver, gallbladder, and pancreas, which add digestive fluids and enzymes to assist in digesting and processing food.
  • The GI tract encounters millions of microorganisms daily, requiring robust defenses.
  • Mucus covers all surfaces of the GI tract, hindering microbial attachment and growth.
  • The GI tract is a mucous membrane, and a lot of IgA is present.
  • Peristalsis moves food and microorganisms through the digestive tract.
  • Saliva contains enzymes like lysozyme and lactoferrin.
  • Stomach acid has a low pH, eliminating many microorganisms.
  • Bile is antimicrobial.
  • The digestive tract contains a lot of protective microbiota.
  • The stomach is thought to be sterile; bacteria found there are usually passing through.
  • Accessory organs should be free of microorganisms.

Definitions: Diarrhea and Dysentery

  • Diarrhea: Three or more loose stools in a 24-hour period.
  • Dysentery: Diarrheal illness with blood and/or mucus in stools.

Stool Sample Collection

  • Need to collect a stool sample to diagnose any of the infections.
  • Ideally, collect in a sterile cup.
  • Avoid contact with urine to prevent contamination and false results.
  • A plastic is placed over the opening of a toilet for a patient to defecate.
  • A collection device is used to collect the stool where at the end of the stick there is a little spoon.
  • The collection device is placed back into the tube, and then it just screws on to keep the stool sample safe from contaminants.
  • Examine color, volume, consistency, or chemical analysis for occult blood.
  • Also analyze fat content, nitrogen content, or if there's any specific enzymes present.
  • Visually or microscopically observe parasites and/or ova.
  • Culture microorganisms, although challenging due to the heavy microbial load.

Cholera

  • Caused by Vibrio cholerae, a gram-negative bacteria with a kidney bean shape and a singular flagella.
  • Incubation: few hours to a few days.
  • Symptoms: Vomiting accompanied by watery feces (secretory diarrhea).
  • Cholera stool is an opaque white liquid without a foul odor, containing flecks of mucus (rice water stool).
  • Can lead to significant loss of body weight (up to 50%).
  • Other effects: loss of blood volume, muscle cramps, severe thirst, flaccid skin, sunken eyes, coma and convulsions (especially in children).
  • If left untreated, death can occur within 48 hours; mortality rate is between 55% and 70%.
  • Infectious dose: 10810^8 cells.
  • The bacteria penetrate the mucus barrier at the junction of the duodenum and jejunum.
  • Bacteria adhere to microvilli of the epithelial cells and multiply.
  • Produce cholera toxin, disrupting normal physiology and causing the intestinal cells to shed a large amount of electrolytes into the intestine, which will then cause profuse water loss.
  • Transmission: Influenced by season and climate; thrives in warm and moist environments; survives in water sources.
  • Endemic in Asia and Latin America; outbreaks often follow natural disasters, war, or refugee movements.
  • Main mode of transmission is the fecal-oral route, usually by consuming contaminated food (undercooked shellfish, contaminated water or ice); rare cases through wounds.
  • Prevention: Vaccine recommended for travelers to affected areas.
  • Treatment: Mild to moderate cases require rehydration and electrolyte replacement.
  • Oral rehydration therapy: Solution of sodium chloride, sodium bicarbonate, potassium chloride, and glucose or sucrose dissolved in water; can restore a patient's condition in four hours without medical facilities.
  • Oral antibiotics can be given along with the rehydration therapy, and this can shorten periods of diarrhea and bacterial excretion.

Shigellosis

  • Caused by species of the Shigella genus (gram-negative).
  • Examples: S. dysentery, flexneri, boidii, and sauniae.
  • Symptoms: Frequent watery stools, fever, intense abdominal pain, nausea and vomiting, dysentery.
  • Infectious dose: 10-20 bacteria.
  • Bacteria invade villous cells of the large intestine, initiating an inflammatory response and tissue destruction.
  • Release of endotoxin (fever) and exotoxins.
  • Enterotoxin: Damages mucosa and villi, leading to bleeding and mucus secretion (dysentery).
  • Shiga toxin: Causes serious damage to the large intestine with systemic effects and injury to nerve cells.
  • Transmission: Fecal-oral route, direct person-to-person contact.
  • Associated with poor sanitation, malnutrition, crowding; chronic carriers can transmit the bacteria.
  • Prevention: Good hygiene.
  • No vaccine available.

Typhoid Fever

  • Caused by Salmonella typhi (gram-negative bacilli).
  • Symptoms: Fever, diarrhea, abdominal pain, and constipation.
  • Four stages:
    • Week 1: Low-grade fever increasing to 103∘F103^\circ F, fatigue, weakness, loss of appetite, abdominal pain.
    • Week 2: High fever, diarrhea, weight loss,