Intro to Medical Microbiology

Question 1

basic differences between viruses, bacteria and fungi

Answer 1

Bacteria are free-living prokaryotic cells that can live inside or outside a body, while viruses are a non-living collection of molecules that need a host to survive. Fungi can be unicellular or multicellular and are eukaryotes.

Question 2

3 domains of life

Answer 2

• Bacteria (prokaryote)
• Archaea (prokaryote)
• Eucarya (Eukaryote)

Question 3

differences between prokaryotes and eukaryotes

Answer 3

• Membrane boud organelles absent in prokaryotes
• Prokaryotes unicellular, eukaryotes mostly multicellular
• Eukaryotes larger
• Porkaryotes simpler (no nucleus, just single chromosome and plasmids)

Question 4

What is microbiology

Answer 4

Study of microorganisms (when applied => medical microbiology)

Question 5

5 causes of microbial infection

(go from most to least common)

Answer 5

• Bacteria
• Viruses
• Fungi
• Parasites
• Prions (proteins)

Question 6

What can the 5 microbial causes of incetion be classified as

Answer 6

• Bacteria - prokaryotes
• Viruses - unclassified
• Fungi - eukaryotic
• Parasites - eukaryotic (usually)
• Prions (proteins) - unclassified

Question 7

Define bacterium

Answer 7

“Chiefly round, spiral or rod shaped single celled prokaryotic organism that typically lives in soil, water, organic matter or the bodies of plants and animals”

Question 8

Define virus

Answer 8

“A unique, acellular, metabolically inert organism that only replicate within living cells”.

Question 9

Define fungus

Answer 9

“Any of a kingdom of saprophytic and parasitic spore-producing eukaryotic typically filamentous organisms including moulds, yeasts, mushrooms and yeasts”

Question 10

Define parasite

Answer 10

“An organism living in, with or on another organism”.

Question 11

Define prion

Answer 11

“Protein of unknown function that resides on the surface of brain cells. An abnormal form of
prion protein that in mammals includes pathogenic forms that arise spontaneously (e.g. genetic
mutation) or transmission (e.g. via infected tissue) and upon accumulation in the brain cause a prion
disease e.g. BSE or CJD.”

Question 12

(Relative) sizes of microorganisms

Answer 12

• Parasites - microscopic to over 30 m
• Fungi - 2 to 10 µm
• Bacteria - 0.2 to 0.5 µm
• Viruses - 20 to 400 nm
• Prions - 10 nm (often measured in Angstrom [1 A = 0.1 nm)

Question 13

speciman types

2

Answer 13

• Sterile sites (shouldn’t contain bacterial flaura)
• Non-sterile sites

Question 14

Give some sterile sites

Answer 14

brain, heart, liver, kidney

Question 15

Give some non-sterile sites

Answer 15

mouth, oesophagus, stomach, lungs, intestine

Question 16

Common specimen types for bacterial culture

Not sure if need to memorise all

Answer 16

• Mid stream specimen of urine (MSSU) - urinary tract infection
• Sputum - lower respiratory tract infection
• Throat swab - tonsillitis / pharyngitis
• Swabs - wound infection, genital tract infection
• Faeces - infectious diarrhea
• Blood culture - septicaemia (sepsis)
• Cerebrospinal fluid CSF) - meningitis
• Aspirate of pus - abscess
• Bone - osteomyelitis.

Question 17

Sterile site

definition

Answer 17

an area where microorganisms are not typically found

Question 18

Non-sterile site

definition

Answer 18

areas where microbes are often found and are usually more accessible from the environment

Question 19

Explain microscopy

Answer 19

• Light microscopy (x1000 magnification)
• Unstained - to see white blood cells (e.g. urine, CSF), to see parasites (faeces)
• Gram stain - to visualise bacteria and yeasts/fungi
• Special stains= Ziehl Neelsen stain or auramine stain for mycobacteria
• Viruses not visible in light microscope!!!

Question 20

What WBC are increased in viral infaction

Answer 20

Lymphocytes

Question 21

What WBC are increased in bacterial infaction

Answer 21

neutrophils

Question 22

Importance of microscopy in clinical setting

Answer 22

Is rapid - urgent info relayed to clinicians. Is not specific but assists provisional diagnosis and empiric antimicrobial therapy

Question 23

Empiric antimicrobial therapy

And definitive therapy

Answer 23

Antibiotics that are administered during the period prior to the receipt of blood culture and antibiotic susceptibility test results
Term “definitive therapy” refers to the antibiotic therapy given subsequent to receipt of these results.

Question 24

What is microscopy followed by

Answer 24

Bacterial culture and susceptibility testing

Question 25

healthcare associated infection

Answer 25

• Prevention is key: onset typically following 48h admission
• S.aureus bacteraemia and C.difficile infection both common hospital infections
• Multi-drug resistant organisms e.g. MRSA, VRE, ESBL, CPE
• Norovirus

Question 26

Infection control measures

Answer 26

• Hand sanitation
• Foam hand sanitizers inside and outside each patient’s room to use on entry and exit
• Disposable paper gowns and latex gloves worn when entering the rooms of immunocompromised patients or patients with dangerous infectious diseases, such as MRSA.
• Aseptic technique when procedures are performed (such as inserting a catheter).

Question 27

Detecting viruses from clinical samples

not sure if need to know everything

Answer 27

• Molecular methods= real time / multiplex PCR
• Antigen detection
• Serology to determine immunity
• Virtually obsolete methods e.g. electron microscopy, cell or tissue culture - inoculate a “cell line”

Question 28

When do we see IgM and IgG antibodies

Answer 28

• IgM - start of infection
• IgG - later on in infection

Question 29

Diagnostic principles in parasitology

Answer 29

• Microscopy of different life cycle stages e.g. parasites, cysts and ova in faeces, blood films for malaria
• Culture rarely possible
• Serology sometimes useful
• Importance of reference laboratories