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Flashcards in Microbiology study guide Deck (21):

Describe Prokaryotes

Small, self replicating single celled microorganisms


Describe eukaryotes

Single celled fungi causing conditions such as thrush


Describe viruses

Small acellular agents consisting of genetic material contained within a protein coat


Describe prions

Infectious protein particles that can alter the shape and behaviour of a host protein


What is the cycle of infection

1. Infectious agent 

(Prokaryote, eukaryote, virus, prion)

2. Resevoir 

(atmosphere, skin, food)

3. Portal of exit

(cough, gut, GI)

4. Mode of transmission

(direct, indirect)

5. Portal of entry

(inhalation, ingestion, injection)

6. Susceptible host



Describe methicillin resistant staphylococcus aureus?

Cause disease with the carriage of proteins that allow it to survive in the presence of more than one antibiotic.

In the nose, mouth and GI tract of healthy individuals

Gram positive cocci, divide in alternate plains to form clumps


Coagulate plasma


Falcutative anaerobe


Describe vancomycin resistant enterococcus faecalis?

High numbers in the GI tract, isolatef from mouth


UTI infections via catheterizaiton, trauma or disease 


Gram positive cocci in chains


Grow in presence of bile 

Lancefield group D antigen 

Falcultative anaerobe


Describe C. diff

Associated with environment and soil

Obligate anaerobes, sensitive to oxygen

Form Spores

Produced in response to stress

Gram positive bacilli 

Produce exoproteins and toxins


Describe HBV

Hepatitis b virus consists of a small double stranded DNA genome encased within a protein caspid (HBc Antigens) and glycoprotein envelope (HBs antigen)


Identified by detection of antigen in serum samples, particularly HBs and HBe


Describe RSV

largely enveloped virus (covered in a lipid bilayer) with a single stranded RNA genome

RT-PCR and detection of viral antigens in immunoassays are used for identification


What is resistance based upon?

genetic variation, natural selection & horizontal gene transfer. 


What is a biofilm?


Organism behaving as part of multi-cellular community.

•  3 dimensional structure

•  Contains interfaces

•  Spatial heterogeneity

•  Permeated by water channels

•  Organisms resistant to antimicrobial agents & host defenses. 


What is a persistor cell?

Give tolerance not resistance

  • Metabolically inert
    • very slow growth
    • Dormant or non-dividing
  • Sub population of cells
    • transient state
    • Planktonic & biofilm populations
    • Enriched in biofilms 


Name two common resistance mechanisms?


enzymes produced by bacteria that provide multiple resistance to B-lactam antibiotics- break the B-lactam ring


Responsible for the resistance seen in MRSA


What would constitite an ideal antibiotic?


  • selective toxicity/minimal toxicity to host
  • cidal
  • long half lide
  • appropriate tissue distribution
  • no adverse drug interactions/side effects
  • oral & parenteral preparations


How do gram negative orgamisms cause shock?

Antigen or endotoxin interact with macrophages

Macrophages release cytokines into blood

Cytokines travel to anterior hypothalamus

Prostaglandin E is released which increases the body's set thermal point

Body starts to think its cold and shivers

Causes fever= increased survival 


Describe Sepsis

  • Small blood vessels become “leaky” and lose fluid into the tissues
  • Lower blood volume requires heart to work harder to maintain oxygenation of tissues (↑HR)
  • Poor tissue oxygen perfusion mean blood supply to less essential organs (skin, kidneys, liver is shut down to try to maintain blood supply to brain
  • Blood clotting system is activated causing blood clotting in tiny blood vessels→ uses up all clotting factors→ increased risk of haemorrhage 


Describe the cell wall of gram positives

Thick multi-layer PG

•  Target of Penicillin 


Describe the cell wall of gram negatives

Outer membrane

– Periplasm
– Thinner PG layer

•  Target of Penicillin 


Describe lipopolysaccharide?

– Outer membrane asymmetric

– Surface nearly all LPS

• Glycolipid

– lipid A
– core polysaccharide

– O-chain/antigen

Structural role
Antigen & Bacterial Toxin 


What is the difference between flagella and fimbriae?

Gm +ve Fimbriae
– non-flagella protein appendages

Gm -ve Pilus
– no motor, Pilin repeated protein unit