Question

Medical Microbiology Tutorial: Introduction to Infectious Organisms

Answer 1

\({\bf{Timeline:}}\)
- 14th-18th centuries: the causes, mechanisms, treatments, and prevention of outbreaks are not well understood
- 1600s: Leeuwenhoek: uses microscope to describe single-celled organisms called "animalcules"
- 1700s: first vaccine invented by Edward Jenner. noticed that milkmaids who contracted cowpox did not generally get smallpox even when their communities did.

- 1800s: "golden age of microbiology"
> evolution of germ theory to challenge the idea of spontaneous generation
> Pasteur's and Koch's experiments establish the foundation of germ theory
> John Snow (no, not the game of thrones guy) observes the cholera epidemic in London and attributes it to infectious agents in contaminated water

- 1900s:
> 1928: Alexander Fleming discovers penicillin has antibiotic properties. (wasn't formally introduced into medicine until like the 1940's)
> 1967: U.S. Surgeon General states that it's "time to close the book on infectious diseases". at this time there had been a steep decline in the # of deaths due to infectious diseases.

Answer 2

\({\bf{Germ~Theory:}}\)
some terms
- spontaneous generation/abiogenesis: the idea that life could develop from inorganic material
- germ theory/biogenesis: certain diseases are caused by living organisms (microorganisms)

Pasteur's Experiment: strong evidence in favor of biogenesis rather than abiogenesis

basic setup:
1. pour a nonsterile liquid into a flask
2. use a torch to make a bend in the neck to trap microorganisms (see diagram)
3. heat the liquid to sterilize, and drive any microorganisms into the bend
4. let liquid cool. the liquid remains sterile, because any infectious agents enter but get trapped in the bend. the liquid itself does not generate new microorganisms
5. tip the flask over, so that the liquid contacts the bent part. liquid becomes nonsterile. shows that it's the microorganisms in the bent part that cause the liquid to become nonsterile.

Answer 3

\({\bf{Germ~Theory,~cont.:}}\)
Koch: formalized the link between infectious organisms and the disease they cause (anthrax, to be more specific)

Known for his 4 postulates to determine whether an organism is truly linked to a disease:

Postulate 1: the organism must be present in all diseased hosts and absent in all healthy hosts.

Postulate 2: the infectious organism must be cultured, and isolated away from the original host

Postulate 3: the isolated culture must be introduced to a healthy host, and cause the same disease

Postulate 4: the infectious organism must be isolated from the host, and must be shown to be identical to the original

Answer 4

\({\bf{Terminology:}}\)
infection: invasion and reproduction of an infectious agent inside a host, and the resulting clinical symptoms
pathogen: an organism/agent that causes disease
commensal: an organism that lives symbiotically with a host
opportunist: an organism that can only be infectious under optimal conditions

types of infections:
endemic infections: infections that are maintained at a baseline level in a certain geographic region without external sources or inputs.
epidemic infections: infections that suddenly increase above the expected baseline level in a certain area or population
hospital-acquired infections: infections acquired during treatment at hospitals or other medical institutions
community-acquired infections: the opposite of hospital-acquired, infections *not* acquired during treatment at hospitals

methods of infections:
1. attach to the host or break physical barriers to enter the host
2. enter host through a vector
3. enter through open wounds
4. infect opportunistically when host immune system is compromised

Answer 5

\({\bf{Defenses~Against~Infection:}}\)
Skin: physical barrier w/ local flora as competition for invading species
Respiratory System: mucus, cilia physically eject invading species
GI tract: low pH is unfavorable for many pathogens, mucus, digesting enzymes, local flora
Urogenital tract: urine flushes out pathogens, and the physical length of the urethra acts as barrier to entry.

\({\bf{Factors~Affecting~Susceptibility:}}\)
- age (being old or young seems to increase susceptibility to infection)
- being immunocompromised (increases susceptibility)
- other health conditions, with diabetes being a major one
- diet/nutrition
- substance abuse
- injuries
- receiving surgery
- having prosthetic material

Answer 6

Sources:

https://patientcarelink.org/improving-patient-care/healthcare-acquired-infections-hais/

https://www.merckmanuals.com/home/infections/biology-of-infectious-disease/defenses-against-infection

http://sphweb.bumc.bu.edu/otlt/MPH-Modules/EP/EP713_History/EP713_History6.html#targetText=John%20Snow%20(shown%20below)%20was,cholera%20in%20a%20systematic%20way.&targetText=In%20fact%2C%20cholera%20is%20caused,that%20is%20contaminated%20with%20sewage.

https://biology-online.org/ (for some definitions)

lecture notes from class