Session 1: Introduction to Infection

Microorganisms can be classified into...

- Bacteria

- Archae

- Fungi

- Helminths + parasites

- Protozoa

- Algae

Non-living pathogens

Viruses and prions

Bacteria are ___

Prokaryotes (no nucleus)

Are archaea prokaryotic or eukaryotic?

Prokaryotic (no nucleus)

Eukaryotes contain what?

A nucleus

Three examples of eukaryotes

Fungi

Algae

Protozoa

Gram positive bacteria stain...

Blue/purple

Gram negative bacteria stain...

Pink/red

Why do Gram positive bacteria stain purple?

Thick layer of peptidoglycan retains the primary stain

Why don't Gram negative bacteria stain purple?

Thin layer of peptidoglycan does not retain the primary stain.

Can be counterstained pink/red.

Some structural differences between Gram negative and Gram positive bacteria

Gram negative

- Thin layer of peptidoglycan = counterstains pink/red

- LPS present

- Outer membrane present

Gram positive

- Thick layer of peptidoglycan = stains purple

- No LPS

- No outer membrane

Is this Gram positive or Gram negative bacteria?

Thick peptidoglycan layer - Gram positive

Is this Gram positive or Gram negative bacteria?

Thin peptidoglycan layer - Gram negative

LPS is present

Why is it important to know if bacteria causing an infection is Gram negative or Gram positive?

Different antibiotics used for different infections due to the structure of the peptidoglycan cell wall

This can confer sensitivity to specific antibiotics

Two examples of Gram negative bacteria

E.coli

Salmonella spp

Two examples of Gram positive bacteria

Staphylococcus aureus

Streptococci

MRSA is an example of a Gram ___ bacteria

Positive

MRSA is treated with...

Vancomycin

Fungi are classified as...

Eukaryotes

Fungi are commonly associated with what specific types of infection?

Opportunistic infections in people who are immunocompromised or immunosuppressed

Examples of diseases caused by fungi

Athlete's foot

Ringworm

Pneumonia (think of CF - opportunistic)

Examples of some fungi

Candida albicans

Cryptococcus neoformans

Aspergillus fumigatus

What are helminths

Large multicellular eukaryotic organisms (worms) that can be free-living or parasitic

Examples of helminths

Tapeworm

Hookworm

Pinworm

Protozoa are classified as...

Eukaryotic, unicellular which can be free-living or parasitic

Examples of some diseases caused by protozoa

Malaria

Toxoplasmosis

Cryptosporidiosis

Trichomoniasis

Examples of some protozoa which cause disease

Plasmodium spp = Malaria

Toxoplasma gondii = Toxoplasmosis

Trichomonas vaginalis = Trichomoniasis

What are the five characteristics of a living organism?

1) One or more cells with DNA

2) Capable of reproducing, growing & developing

3) Capable of capturing & using energy/raw materials

4) Able to sense/respond to environment

5) Capable of evolving over generations

What is a prion

An infectious misfolded protein

Why are prions not considered as living infectious agents?

Prions do not contain any nucleic acids such as DNA/RNA so it is non-living

Example of disease caused by prion protein

Creutzfeldt-Jakob Disease (CJD)

Example of causes of acquired CJD (rare)?

Blood transfusions

Contaminated instruments in brain surgery

Infected tissue transplants

Can prion diseases be genetic?

Prion diseases can be sporadic, genetic or acquired

Describe structure of viruses

Acellular (non-living)

Contain short strands of genetic material (DNA/RNA)

Encapsulated with protein coat

Why are viruses considered non-living?

They cant survive or reproduce on their own, and are not made of cells.

Two ways in which viruses are classified?

1) Baltimore classification = based on manner of m-RNA synthesis

2) Whether viral genome is DNA or RNA based

Give three examples of DNA viruses and the associated disease they cause

1) Herpes simplex virus = Cold sores, herpes

2) Varicella-Zoster virus = Chickenpox

3) Hepatitis B virus = Hepatitis

Give three examples of RNA viruses and the associated disease they cause

1) HIV virus = HIV, AIDS

2) Influenza virus = Influenza

3) Coronavirus = Covid-19, SARS, MERS

Name two eukaryotic infectious agents

Bacteria

Protozoa

What are the main differences between Gram positive and Gram negative bacteria?

Gram positive stain purple with crystal violet dye due to thick peptidoglycan wall.

Gram negative bacteria do not stain purple, but are counterstained red/pink (thin peptidoglycan wall).

Gram negative bacteria also have LPS present and have an outer membrane present, unlike gram positive which do not.

Give an example of Gram negative bacteria

E.coli

Salmonella spp

Name one disease caused by fungi

Athlete's foot

Explain why viruses aren't classed as living organisms

Viruses cannot reproduce without a host cell.

Viruses lack the machinery needed to carry out the functions of life. therefore, they are classified as non-living infectious agents and are not placed in the biological classification system.

Streptococcus bacteria are gram negative

True or false?

False

When classifying Escherichia coli using the hierarchic scale, Class, Order, Family, Genus or Species, which group is the coli assigned to?

Species

When considering relative sizes, which pathogen is the smallest?

Virus

What category of bacterial pathogen exploits the deficiencies of immunocompromised hosts to become pathogens?

Opportunistic

3 multiple choice options

When classifying microbes, to which group would you associate the term mycology?

Fungi

3 multiple choice options

Infectious agents can be classified as cellular or acellular.

An example of a acellular infectious agent may include...

Prion

3 multiple choice options

The majority of microbes which can cause human infection are found to have a cellular structure including organelles, however some infectious agents do not have organelles.

Which organism might this be?

Virus

3 multiple choice options