Small, self replicating single celled microorganisms
Single celled fungi causing conditions such as thrush
Small acellular agents consisting of genetic material contained within a protein coat
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)
(atmosphere, skin, food)
3. Portal of exit
(cough, gut, GI)
4. Mode of transmission
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
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
Describe C. diff
Associated with environment and soil
Obligate anaerobes, sensitive to oxygen
Produced in response to stress
Gram positive bacilli
Produce exoproteins and toxins
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
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
- 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
- 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
– Thinner PG layer
• Target of Penicillin
– Outer membrane asymmetric
– Surface nearly all LPS
– lipid A
– core polysaccharide
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