Intro To Infection Flashcards
What is a virus?
- Unique, acellular, metabolically inert organism that only replicate within living cells
- unclassified type of cell
- 20-400 nm
What is bacteria
-chiefly round, spiral or rod shaped single called prokaryotic organism that typically lives in soil, water, organic matter or the bodies of plants and animals
- 0.2 to 0.5 um
What is fungi
- Any kingdom of saprophytic and parasitic spore-producing eukaryotic typically filamentous organisms including moulds, yeasts and mushrooms
Micro-organisms that cause infection
- Bacteria
- viruses
- fungi
- parasites
- prions
Common specimen types collected for culture
- Mid stream specimen of urine ~ urinary tract infection
- sputum ~ lower respiratory tract infection
- throat swab ~ tonsillitis/pharyngitis
- swabs ~ wound infection/ genital tract infection
- faeces - infectious diarrhoea
- blood culture ~ septicaemia
- cerebrospinal fluid ~ meningitis
- aspirate of pus ~ abscess
- bone ~ osteomyelitis
Role of microscopy and culture in the diagnosis of bacterial infection
- Unstained ~ to see while blood cells and parasites
- GRAM stain ~ to visualise bacteria and yeasts/fungi
- followed by bacterial culture and susceptibility testing
Difference between sterile and non sterile sites
- Sterile sites (no commensal flora): brain, heart, liver, kidney
- non sterile sites: mouth, oesophagus, lungs, stomach, intestine
Methods of detecting viruses
- Molecular methods: real time / multiplex PCR
- antigen detection
- serology to determine immunity (using serum)
Diagnostic principles in parasitology
- Microscopy of different life cycle stages
- culture rarely possible
- serology sometimes useful
- importance of reference laboratories
Basic infection control measures
F ~ face coverings
A ~ avoid crowded places
C ~ clean hands regularly
T ~ two metre distance
S ~ self isolate
How can bacteria be identified?
- Gram staining
Positive - purple
Negative - pink
Shape: cocci-spherical,
bacilli - rod shaped,
spiral-corkscrew
Structure and function in bacteria cells: chromosome
- single chromosome
- Contains genetic information
Cytoplasmic membrane
- 5 -10 nm thick
- made of phospholipids (40%) and proteins (60%)
- allows passage of water and small uncharged molecules
Cell wall
- 10-25 mm thick
- made of peptidoglycan
- thick, strong and relatively rigid-maintains shape
- if cell wall is weekend or ruptured - osmosis means lysis will occur
Ribosome
- Consider of RNA and associated proteins
- synthesise proteins
- divided into subunits
- Bacteria have a 70s ribosomes with large (50s) and small (30s) subunits
Peptidoglycan
~ N-acetylglucosamine acid and n-acetylmuramic acid molecules linked alternately in a chain, with short peptides forming cross-links
Lipopolysaccharide outer membrane
- Only in gram negative bacteria
- protects peptidoglycan from bile salts and lysozyme
- blocks antibiotics from getting into cue
- lipid A may give rise to endotoxic shock when released into bloodstream
Capsule
- polysaccharide wall outside bacteria
Flagella
- Long filament twisted spirally
- gives bacterial ell mobility
A… (1)
B.. (one point)
C… (both sides)
D… (all over)
Fimbriae
- Gives adherence
- between bacterial cus and host cells
- numerous but shorter than flagella
Plasmid
- Contain genetic info
- genetic variation through transfer of plasmids or spontaneous mutation
Bacteriophage
- Virus that infects bacteria
- destroys host cells
- burst out by lysis
Spores
Classification and nomenclature used for bacterial species
Classification:
phenotypic (gram stain, growth requirements, serologic, mass spectrometry)
Genotype cribosomai raw sequence analysis, whole genome sequencing)
Nomenclature:
Genus + species
Difference between gram negative and gram positive bacteria
Gram positive:
plasma membrane (contains proteins)
pepticloglycan
Gram negative:
plasma membrane contains proteins)
Periplasmic space
Peptidoglycan
Periplasmic space
Outer membrane (contains proteins + LPS)
How bacteria replicate and create genetic variation
Conjugation:
1. F pillus On F + attaches to receptor of F minus
2. Combine and endonuclease goes to origin on transfer on plasmid
3. A strand of plasmid moves to F minus celI
4. Complimentary strand is synthesised
5. Eventually all cells become A plus
Detection and culture of bacteria
- Individual Bactria can only be seen using microscope
- colonies can be cultured on solid medium (agar)
- Basic classification and characterisation of viruses
- Small 20 -400 mm
- non cellular (cannot replicate independently)
- icosaheddral: 20 faces
- helical
- complex
Principles of viral culture
Examples of human virus infections of major importance
- EBV
- Human herpes
- Human T-cell lymphotropic virus
- hpv
- hepatitis B and C
Structure of viruses
- nucleic Acid
- Vision associated polymerase
- protein capsid
- lipid envelope
- spike projections
How viruses replicate
Find video
Concept of host range in relation to viruses
- Some viruses only infect humans eg. Smallpox, measles
- some may also infect other animals/birds:
~ transmission of novel virus to humans
~ confection of human and animal or bird strains in one organism may lead to recombination and
Generation of new strain
Consequences of viral infection
- Clearance of virus
- chronic infection
- latent infection
- transformation
Concept of viral latency
- Following primary infection, some viruses lie dormant in the cell
-The full viral genome is retained in the host cell, but its expression is restricted, such that few viral antigen and no viral particles are produced
- reactivation of viral replication can occur
- reactivations may or may not cause apparent disease
- reactivation more likely to occur and more severe in immunocompromised
Link between viruses and cancer + mechanism through which this results
- A number of viral infections can lead to cancer
Mechanism:
- modulation of cell cycle (driving cell proliferation)
- modulation of apoptosis (prevention)
-Reactive oxygen species mediated damage (some persistent viral infections can cause persistent inflammatory processes which lead to cancer via reactive oxygen species)
Indications for and principles of anti-viral therapy
- Only used in a minority of viral infections
- can be used for: prophylaxis (to prevent infection), pre-emptive therapy (evidence of infections replication detected, befor symptoms are apparent)
- overt disease
- suppressive therapy (keep below rate that can cause tissue damage in asymptomatic patient)
How to prevent viruses
- Immunisation
- prophylactic treatment post exposure
- facts
- blood / tissue, organ screening
- antenatal screening
- What is meant by the term vaccination
- Administration of antigenic material to stimulate un individuals immune system to develop adaptive immunity to a pathogen
Types of vaccines available for active immunisation
Contra-indications to vaccination
- Temporary: febrile illness, pregnancy
- permanent: allergy, immunocompromised
How immune response occurs
Concept of herd immunity
- Vaccinated individuals being less likely to be a source of infection to others
- reduces risk of unvaccinated being exposed
Vaccination schedules for children
See goodnotes
Vaccines that may need to be given to travellers
- Hepatitis A
Typhoid
Neisseria meningitidis
Cholera
Yellow fever
Japanese encephalitis
Tick-borne encephalitis
Rabies
Main groups of parasites
Protozoa
Helminths (worms)
Ectoparasites
Diseases caused by enteric and blood-borne parasites
Malaria
Diagnostic principles of parasitology
What is a parasite?
- Organism that lives in or on a host and derives its nutrients at expense of this host
Protozoa
- Malaria, amoebae, flagellates
- microscopic, single-celled organisms
- can be free-living or parasitic in nature
- able to multiply in humans
- transmission
Helminths
- Roundworms, tapeworms, flukes
- nematode (roundworm) eggs hatch in intestinesoften asymptomatic, mass can obstruct bile duct or small intestine,
- Cestodes (tapeworms) larval cysts ingested,
Adult tapeworms in human, - trematodes (flukes/flatworms) schistosomiasis, contact with freshwater where snail intermediary host present
Ectoparasite’s
- Live outside body
