Microbial diseases, Kochs postulate

Question 1

name some microbial pioneers

Answer 1

• Germ theory of disease: microorganisms can cause disease and it can spread and reemerge
• Antonie van Leeuwenhoek (1670s): observed bacteria for the first time
• Louis Pasteur (1822): proved yeast are living organisms, fermenting wine
• Robert Koch (1876): proved bacteria cause disease

Question 2

Anthrax

Answer 2

• The disease anthrax was very prevalent in farm animals
• Anthrax coagulates and darkens the blood of infected animals (anthrac: “coal”)
• Koch thought Bacillus anthracis was the cause

Question 3

what is Koch’s Postulates

Answer 3

1. The microorganism must be found in abundancein all organisms suffering from the disease butshould not be found in healthy animals.
2. The microorganism must be isolated from adiseased organism and grown in pure culture.
3. The cultured microorganism should causedisease when introduced into a healthyorganism.
4. The microorganism must be re-isolated from theinoculated, diseased experimental host andidentified as being identical to the originalmicroorganism.

Question 4

Infection of the stomach lining by Helicobacter pylori

Answer 4

• Gram-negative, motile, transmitted orally
• Remarkable ability to resist pH 1 conditions
• Causes stomach diseases – ulcers and cancers

Question 5

Infection to Ulcer

Answer 5

• Ingestion – and flagella propel pathogen to mucosa
• It produces urease – converting urea to CO2 and ammonia (reduces acidity in the local area)
• Makes enzymes to soften mucous lining – allows access to epithelial layer
• The lower level of acidity allows growth and division of bacterium but this causes inflammation and damage to the stomach lining

Question 6

Chlamydia

Answer 6

• Caused by: bacterium Chlamydia trachomatis* Prevalence: The most common bacterial STI in the US (3-4 million new cases a yr. in US)
• Transmission: primarily penile-vaginal, oral-genital, oral-anal, or genital-anal contact;can also be spread by fingers from one body site to another.* Symptoms:
• In majority of cases, none!
• if present:
  *Women: mild irritation or itching, burning urination, slight vaginal discharge
  * Men: urethral discharge, burning urination

Question 7

Syphilis

Answer 7

• Caused by: bacterium Treponema pallidium
  Gram-negative bacterium
  Distinctive helical shape – spirochete family
  Endoflagellum found in the periplasmic space rendering the bacteriummotile in a spiral fashion
  Microaerophillic (needs low oxygen levels)
  Limited genome and relies on the host for nutrients
• Prevalence: ~700,000 new cases a yr. in US
• Transmission: penile-vaginal, oral-genital, oral-anal, or genital-anal contact

Question 8

Pseudomembranous colitis

Answer 8

Large intestinal disease caused by Clostridioides (formerly Clostridium) difficile.
Can develop from the more common antibiotic-associated diarrhea
Clostridium difficile forms two toxins (TcdA and TcdB) which inactivate small GTPases.
This causes actin condensation, cell rounding, and cell death causing exudative plaques to form on the intestinal wall.

Question 9

Clostridioides difficile

Answer 9

One pathogen + one colonization resistor = no disease

Clostridioides cinders is a commensal associated with colonization resistance of C. difficile

Coloured scanning electron micrograph of Clostridioides difficile bacterial cells (yellow), a common cause of antibiotic-associated diarrhoea in hospitalized patients

Question 10

what are routes to infection

Answer 10

Gastrointestinal tract
Respiratory Tract
Wounds or abrasions in mucous membranes or skin
Genitourinary Tract
Parenteral

Question 11

chemical barriers to infection

Answer 11

defensins - cationic peptides
29-46 amino acids
destroy microbes cytoplasmic membrane
peptide binds negatively charged outer membrane
then pulled into the cytoplasmic membrane