Microorganisms and Infectious Diseases

Study Notes

Types of Microorganisms that Cause Infectious Diseases

Bacteria belong to the prokaryote kingdom
Fungi (yeasts and molds) belong to the kingdom of fungi
Protozoa are members of the kingdom of protists
Helminths (worms) are classified in the animal kingdom
Viruses are not classified in any of the above kingdoms

Pathogenicity and Virulence

Pathogenicity: the ability of a bacterial species to cause disease in a susceptible human host
Virulence: a term that presumes pathogenicity, but allows for expression of degrees of virulence
Degrees of virulence:
- Low virulence: Streptococcus salivarius, universally present in the oropharyngeal flora, but rarely causes disease
- Moderate virulence: Escherichia coli, found in the colon, causes acute infection if displaced to other sites
- High virulence: Bordetella pertussis, causes whooping cough, highly infectious and causes disease in almost every non-immune person
- Extremely high virulence: Yersinia pestis, causes plague, highly infectious and leads to death in a few days in over 70% of cases

Stages of Infection

Transmission from an external source into the portal of entry
Evasion of primary host defenses (e.g. skin or stomach acid)
Adherence to mucous membranes using bacterial pili
Colonization by growth of bacteria at the site of adherence
Disease symptoms caused by toxin production or invasion accompanied by inflammation
Host responses (nonspecific and specific immunity) during steps 3-5
Progression or resolution of the disease

Waterborne Diseases

Transmission of important waterborne diseases:
- Salmonella species: diarrhea, ingested through contaminated water
- Shigella species: diarrhea, ingested through contaminated water
- Campylobacter jejuni: diarrhea, ingested through contaminated water
- Pseudomonas aeruginosa: folliculitis, penetrated through skin, associated with hot tubs

Foodborne Diseases

Bacterial diseases transmitted through foods:
- Staphylococcus aureus: food poisoning, especially in mustard-filled pastries, potato, egg, or tuna fish salad
- Bacillus cereus: diarrhea, reheated rice
- Clostridium perfringens: diarrhea, cooked meat, stew, and gravy
- Escherichia coli O157:H7: hemorrhagic colitis, hemolytic-uremic syndrome (HUS), undercooked meat
- Salmonella typhi: typhoid fever, various foods
- Vibrio cholerae: diarrhea, various foods, especially seafood, and water
- Clostridium botulinum: botulism, improperly canned vegetables and smoked fish

Zoonotic Diseases Caused by Bacteria

Bacterial diseases transmitted from animals to humans:
- Bacillus anthracis: anthrax, direct contact with infected animals
- Listeria monocytogenes: infection in neonates or mothers, ingestion of unpasteurized milk products
- Brucella species: brucellosis or Malta fever, ingestion of unpasteurized milk products, contact with animal tissues
- Mycobacterium bovis: intestinal tuberculosis, ingestion of unpasteurized milk products

Description

This quiz covers the basics of microorganisms that cause infectious diseases, including bacteria, fungi, protozoa, helminths, and viruses. It also explores pathogenicity and virulence in microorganisms.