Intro to Microbiology Flashcards
Eukaryotic species
A group of closely related organisms that breed among themselves
Prokaryotic species
A population of cells w/ similar characteristics
Clone
Population of cells derived from a single cell
Strain
Genetically different cells within a clone
Viral species
Population of viruses w/ similar characteristics that occupies a particular ecological niche
Gram stain +ve and -ve
Bacteria to be characterised as Gram +ve if they retain the violet dye (peptidoglycan layer) or Gram -ve if they don’t (lipopolysaccharide layer)
Process of the Gram stain
Crystal violet –> iodine treatment –> decolorisation
Microorganism shapes
Round cells are called cocci (sing. coccus)
Rod-shaped cells are bacilli (bacillus)
Acid Fast Bacilli stain
Mycobacteria aren’t stained during gram test due to mycolic acid layer in membrane. Waxy layer that is v. thick and very dense so doesn’t even pick up pink colour
Process of acid fast bacilli stain
Apply primary stain of carbolfuschin for 30 seconds
Heat fix cells to the slide using the flame
Decolorize with acid alcohol for 15-20 seconds
Apply counterstain of methylene blue for 30 seconds then rinse excess stain
Other ways to classify bacteria
Classification by phenotype
Classification by genotype
Classification by analytical methods
Classification of bacteria by phenotype
How they behave w/ diff substrates/ Abx
Latex agglutination
Classification of bacteria by genotype
G + C ratio
DNA hybridisation
DNA fragment analysis
Whole genome sequencing
Classification of bacteria by analytical methods
Whole cell lipids
Cell wall
Whole cell protein (proteomics)
Mycoses
Infections caused by fungi
Arguments for viruses being living
Can mutate
Reproduce, only in living host cells
Respond to environmental stress
Arguments for viruses being non-living
Acellular; no cytoplasm or cellular organelles
Carry out no metabolism on their own – use host mechanisms. New viral components are synthesized and assembled within infected host cell
Vast majority of viruses possess either DNA or RNA not both
Prions
Protein containing particles w/ no detectable nucleic acid
‘Slow’ infectious diseases
Highly resistant infectious agent
No inflammation or immune response in affected
Antibiotic susceptibility
Create ‘lawn’ of bacteria
Add filter disc w/ known quantity of antibiotic
Inhibition of growth around disc
‘Cut - off’ size of zone correlates to conc. of antibiotic in blood following normal dose
Non-culture methods
Look for antigen
Look for antibody
Look for genome
Looking for antigen
Known antibody will bind to antigen in sample
ELISA
Immunofluorescence
Looking for antibody
Know antigen will bind to antibody in sample
ELISA
CFT
Looking for genome
PCR: detect known sequence of DNA/RNA within sample
‘Fingerprinting’: compare DNA fragments w/ reference stains
Examples of Abx resistant microorganisms
MRSA
C. difficile
ESBL bacteria
VRE
MRSA
A Staphylococcus aureus that is methicillin and therefore penicillin, flucloxacillin resistant
C. difficile
Anaerobic bacterium that lives in gut
Can become deregulated via the use of broad-spectrum antibiotics and overgrow causing pseudomembranes and colitis
ESBL bacteria
Extended Spectrum Beta-lactamases
Gram -ve Enterobacteriaceae that are resistant to all penicillin-based Abx
Usually complicate urinary catheter and in situ drains
VRE
Vancomycin-resistant enterococcus
Commensal bacteria but can cause infections of the urinary tract, the bloodstream, or of wounds associated w/ catheters or surgical procedures
Usually causes infections on hosp
Causes of antibiotic resistance
Over-prescription of antibiotics
Patients not finishing entire antibiotics course
Antibiotics in livestock and fish farming
Poor infection control in healthcare settings
Poor hygiene and sanitation
Absence of new antibiotics being discovered
How do organisms cause disease
Invasion and damage to host cells; cell death and infl response –> toxin production (systemic or local) —> response to infection; “immune mediated”
Types of innate defences
Mechanical
Chemical
Cellular
Mechanical innate defences
Respiratory tract
GI tract
Skin
Respiratory tract as a mechanical innate defence
Nasal hair URT anatomy Secretions Epithelial sloughing Muscociliary apparatus Expulsion
Muscocilliary expulsions
Uses motion of ciliated epithelium to bring out bacteria
GI tract as mechanical innate defence
Secretions
Epithelial sloughing
Peristalsis
Elimination
Skin as mechanical innate defence
Waterproofing
Tight junctions
Chemical innate defences
Lysozyme
Iron binding proteins e.g. lactoferrin
Defensins e.g. cathelicidins
Surfactant
Chain of infection
Microbe —-> Reservoir —> Escape route —-> Transmission —> Point of entry —> Host —->
Reservoir
Place where infection is prevalent
Can be animal
Esacpe route
How microbe spreads from reservoir
What does the environment classify
Transmissibility of viruses by the environment they spread from
Airborne spread
Tiny particles 1-5 micrometres Cough aerosol Remain suspended in air indefinitely Can reach alveoli easily Low numbers but high virulence organisms e.g. TB, measles
Droplet spread
Remain suspended for 17 mins
Deposit in upper airway
1m spread
Impact on mucous membrane
Person to person transmission
Direct contacts - skin to skin Faecal-oral Inhalation Sexual transmission Blood to blood Vertical
Examples of vertical transmission
Mother to foetus
Mother to baby
Fomite
An inanimate object that is capable of transmitting infectious organisms from one individual to another e.g. keyboard
Vertical transmission routes
Mother’s bloodstream
Mother’s genital tract
Breast-feeding
What your does Gram-ve bacteria stain
Pink
