Q4MBIO | LESSON 5

• Essentially a tubelike structure, the gastrointestinal (GI) tract or alimentary canal– mainly the mouth, pharynx (throat), esophagus, stomach, and the small and large intestines.

  Digestive System
• The purpose of the digestive system is to digest food; break them down into small molecules that can be taken up and used by body cells.

  Digestive System
• • Bacteria heavily populate most of the digestive system.
  • The stomach and small intestine have relatively few microorganisms because of the hydrochloric acid produced by the stomach and the rapid movement of food through the small intestine.

  Normal Microbiota of the Digestive System
• The large intestine has enormous microbial populations, exceeding 100 billion bacteria per gram of feces. (Up to 40% of fecal mass is microbial cell material.)

  The population of the large intestine is composed mostly of anaerobes and facultative anaerobes. Most of these bacteria assist in the enzymatic breakdown of foods. Some of them synthesize useful vitamins.

  Normal Microbiota of the Digestive System
• The small intestine also contains important antimicrobial defenses, most significantly, millions of specialized, granule-filled cells called Paneth cells.

  Normal Microbiota of the Digestive System
• Bacterial Diseases of the Mouth

  1. Periodontal Disease
  2. Dental Caries
  3. Acute Necrotizing
• Pathogen – Various, primarily Porphyromonas spp.

  Symptoms – Bleeding gums, pus pockets

  Treatment – Removal of damaged area; antibiotics

  Prevention – Plaque removal

  Periodontal Disease
• Pathogen – Primarily Streptococcus mutans

  Symptoms – Discoloration or hole in tooth enamel

  Treatment – Removal of decayed area

  Prevention – Brushing, flossing, reducing dietary sucrose– Plaque removal

  Dental Caries
• Dental Plaque – A type of biofilm and are intimately involved in the formation of dental caries, or tooth decay.

  Oral bacteria convert sucrose and other carbohydrates into lactic acid, which in turn attacks the tooth enamel.

  Dental Caries
• Streptococcus mutans – A gram-positive coccus; capable of metabolizing a wide range of carbohydrates; tolerates a high level of acidity; synthesizes dextran, a gummy polysaccharide of glucose molecules which is an important factor in the formation of dental plaque.


  Dental Caries
• Older, calcified deposits of plaque are called dental calculus or tartar.

  Decayed area eventually advances to the pulp which connects with the tissues of the jaw and contains the blood supply and the nerve cells.

  Dental Caries
• If untreated, the infection may advance from the tooth to the soft tissues, producing dental abscesses caused by mixed bacterial populations that contain many anaerobes.

  Dental Caries
• • Conditions characterized by inflammation and degeneration of structures that support the teeth.
  • Gingivitis can progress to this chronic condition that generally causes little discomfort. The gums are inflamed and bleed easily. Sometimes, pus forms in periodontal pockets surround the teeth.
  • The roots of the tooth are protected by covering of specialized connective tissue called cementum.

  Periodontal Disease
• • Bleeding of gums while the teeth are being brushed.
  • It has been shown experimentally that gingivitis will appear in a few weeks if brushing is discontinued and plaque is allowed to accumulate.
  • An assortment of streptococci, actinomycetes, and anaerobic gram-negative bacteria predominate in these infections.

  Gingivitis
• • Also called Vincent' s disease or trench mouth.
  • The disease causes enough pain to make normal chewing difficult. Foul breath also accompanies the infection.
  • Among the bacterias usually associated with this condition is Prevotella intermedia.
  • Because these pathogens are usually anaerobic, treatment with oxidizing agents, debridement, and the administration of metronidazole or antibodies may be temporarily effective.

  Acute Necrotizing Ulcerative Gingivitis
• Infection

  • Occurs when a pathogen enters the GI tract and multiplies.

  Gastroenteritis

  • Applied to diseases causing inflammation of the stomach and intestinal mucosa.

  Temperature Abuse

  • Microbes reproduce and release enterotoxin into the food.

  Intoxication

  • Caused by the ingestion of such a preformed toxin.

  Botulism

  • A special case of intoxication because the ingestion of the preformed toxin affects the nervous system rather than the GI tract.

  Bacterial Diseases of the Lower Digestive System
• Daniel Salmon

  • Discovered the Salmonella bacteria

  Dysentery

  • Severe diarrhea accompanied by blood or mucus.

  Kiyoshi Shiga

  • Japanese microbiologist
  • Shigella genus was named after him

  Bacterial Diseases of the Lower Digestive System
• Pathogen – S. aureus

  Symptoms – Nausea, vomiting, and diarrhea

  Intoxication / Infection – Intoxication (enterotoxin)

  Diagnostic Test – Phage typing

  Treatment – None

  Staphylococcal Food Poisoning
• Pathogen – Shigella spp.

  Symptoms – Tissue damage and dysentery

  Intoxication / Infection – Infection (endotoxin and Shiga toxin, exotoxin) Diagnostic Test – Isolation of bacteria on selective media

  Treatment – Quinolones

  Shigellosis (bacillary dysentery)
• Pathogen – Salmonella enterica

  Symptoms – Nausea and diarrhea

  Intoxication / Infection – Infection (endotoxin)

  Diagnostic Test – Isolation of bacteria on selective media, serotyping

  Treatment – Oral rehydration

  Salmonellosis
• Pathogen – Salmonella typhi

  Symptoms – High fever, significant mortality

  Intoxication / Infection – Infection (endotoxin)

  Diagnostic Test – Isolation of bacteria on selective media, serotyping Treatment – Quinolones; cephalosporins

  Typhoid Fever
• Pathogen – Vibrio cholerae

  Symptoms – Diarrhea with large water loss

  Intoxication / Infection – Infection (exotoxin)

  Diagnostic Test – Isolation of bacteria on selective media

  Treatment – Rehydration, doxycycline

  Cholera
• Pathogen – V. parahaemolyticus

  Symptoms – Choleralike diarrhea, but generally milder

  Intoxication / Infection – Infection (enterotoxin)

  Diagnostic Test – Isolation of bacteria on 2–4% NaCl

  Treatment – Rehydration, antibiotics

  Vibrio parahaemolyticus Gastroenteritis
• Pathogen – V. vulnificus

  Symptoms – Rapidly spreading tissue destruction

  Intoxication / Infection – Infection

  Diagnostic Test – Isolation of bacteria on 1% NaCl

  Treatment – Antibiotics

  V. vulnificus Gastroenteritis
• Pathogens

  1. EPEC – Enteropathogenic E. coli

  • Major cause of diarrhea in developing countries and is potentially fatal in infants.

  2. EIEC – Enteroinvasive E. coli

  • Essentially synonymous with Shigella– it has the same pathogenic mechanisms.

  3. EAEC – Enteroaggregative E. coli

  • Group of coliforms found only in humans.

  4. ETEC – Enterohemorrhagic E. coli

  • Shiga-toxin producing E. coli

  E. coli Gastroenteritis
• Symptoms – Watery diarrhea

  Intoxication / Infection – Infection (exotoxin)

  Diagnostic Test – Isolation on selective media, DNA fingerprinting

  Treatment – Oral rehydration

  E. coli Gastroenteritis
• Pathogen – Helicobacter pylori

  Symptoms – Peptic ulcers

  Intoxication / Infection – Infection

  Diagnostic Test – Urea breath test, bacterial culture

  Treatment – Antimicrobial drugs

  Helicobacter Peptic Ulcer Disease
• Pathogen – Campylobacter jejuni

  Symptoms – Fever, abdominal pain, diarrhea

  Intoxication / Infection – Infection

  Diagnostic Test – Isolation in low O2, high O2

  Treatment – None

  Campylobacter Gastroenteritis
• Viral Diseases of the Digestive System

  1. Mumps
  2. Viral Gastroenteritis (Rotavirus)
  3. Viral Gastroenteritis (Norovirus)
• Pathogen – Mumps virus, Paramyxoviridae

  Symptoms – Painful swelling of parotid glands

  Incubation Period – 16-18 days

  Diagnostic Test – Symptoms; virus culture

  Treatment – Preventive vaccine

  Mumps
• Pathogen – Rotavirus

  Symptoms – Vomiting, diarrhea for 1 week

  Incubation Period – 1-3 days

  Diagnostic Test – Enzyme immunoassay for viral antigens in feces Treatment – Oral rehydration

  Viral Gastroenteritis (Rotavirus)
• Pathogen – Norovirus

  Symptoms – Vomiting, diarrhea for 2-3 days

  Incubation Period – 18-48 days

  Diagnostic test – PCR

  Treatment – Oral rehydration

  Viral Gastroenteritis (Norovirus)
• • An inflammation of the liver.
  • Also an occasional result of infections by other viruses such as Epstein-Barr virus or cytomegalovirus.

  Hepatitis
• Pathogen – Hepatitis A virus, Piconaviridae

  Symptoms – Mostly sub-clinical; fever, headache, malaise, jaundice in severe cases, no chronic disease

  Incubation Period – 2-6 weeks

  Method of Transmission – Ingestion

  Diagnostic Test – IgM antibodies

  Treatment – Immunoglobulin

  Vaccine – Inactivated virus. Post-exposure immune globulin

  Hepatitis A
• • Pathogen – Hepatitis B virus, Hepadnaviridae
  • Symptoms – Frequently subclinical; similar to HAV, but no headache, more likely to progress to severe liver damage, chronic disease occurs
  • Incubation Period – 4-26 weeks
  • Method of Transmission – Parenteral; sexual contact
  • Diagnostic Test – IgM antibodies
  • Treatment – Interferon alfa and nucleoside analogs
  • Vaccine – Genetically modified vaccine produced in years

  Hepatitis B
• • Pathogen – Hepatitis C virus, Flaviviridae
  • Symptoms – Similar to HBV, more likely to become chronic
  • Incubation Period – 2-22 weeks
  • Method of Transmission – Parenteral
  • Diagnostic Test – PCR for viral RNA
  • Treatment – Peginterferon and ribavirin
  • Vaccine – None

  Hepatitis C
• • Pathogen – Hepatitis D virus, Deltaviridae
  • Symptoms – Severe liver damage, high mortality rate; chronic disease may occur
  • Incubation Period – 6-26 weeks
  • Method of Transmission – Parenteral; requires coinfection with hepatitis B
  • Diagnostic Test – IgM antibodies
  • Treatment – None
  • Vaccine – HBV vaccine is protective

  Hepatitis D
• • Pathogen – Hepatitis E virus, Caliciviridae
  • Symptoms – Similar to HAV, but pregnant women may have high mortality, no chronic disease
  • Incubation Period – 2-6 weeks
  • Method of Transmission – Ingestion
  • Diagnostic Test – IgM antibodies, PCR for viral RNA
  • Treatment – None
  • Vaccine – HAV vaccine is protective

  Hepatitis E
• Fungal Diseases of Digestive System

  1. Ergot Poisoning
  2. Aflatoxin Poisoning
• • Pathogen – Aspergillus flavus
  • Symptoms – Liver cirrhosis; liver cancer
  • Reservoir or Host – Mycotoxin produced by fungus growing on food
  • Diagnostic Test – Immunoassay for toxin in food
  • Treatment – None

  Aflatoxin Poisoning