Bacterial properties and disease Flashcards
Meanings of coccus, bacillus, spirillus
Coccus - spherical
Bacillus - Rod-shaped
Spirillus - spiral
Gram-negative bacteria features and colour under Gram stain
- Cell wall has two membranes with a thin peptidoglycan layer sandwiched between membranes.
- Lipopolysaccharide in outer membrane which resists the dye.
- Appear violet after stain
Examples of Gram-negative bacteria
Escherichia coli Salmonella Shigella Vibrio cholerae Neisseria
Gram-positive bacteria features and colour under Gram stain
- Cell wall has one membrane with a thick peptidoglycan layer and teichoic and lipoteichoic acid.
- Peptidoglycan retains the dye.
- Appear deep purple after stain
Examples of Gram-positive bacteria
Staph. aureus
Strep. pneumoniae
Strep. pyogenes
Acid-fast bacteria features and colour under Gram stain
- Cell wall has one membrane, a thin peptidoglycan layer, and mycolic acid.
- Mycolic acid helps cell wall resist dye.
- Appear light purple under Gram stain
Aerobic bacteria feature
Require oxygen for survival
Anaerobic bacteria feature
Do not require oxygen for survival
Bacterial life cycle stages
- Colonise in host
- Persist by finding unique niche and avoid host defences
- Replicate using nutrients from the host
- Disseminate throughout tissues
- Cause disease by producing toxins/inducing diarrhoea/deregulate immune responses
Extracellular bacteria examples
Staphylococcus
Streptococcus
Yersinia
Neisseria
Intracellular bacteria examples
- Phagocytosed by host cell and proliferate inside host cell
- Coxiella - survives in phagolysosome upon uptake
- Salmonella, mycobacteria - survive by preventing fusion of lysosomes with endo-/phagosome
- Listeria, shigella - escape from endo-/phagosome
Salmonella’s techniques of motility and invasion
- Uses flagellum for movement
- Possesses an injectisome which transfers virulence proteins into the host cell.
Listeria’s techniques of motility and invasion
- Uses actin cytoskeleton of host cell to move intracellularly and spread from cell to cell
- Escapes the endoscope and reorganises the cytoskeleton of the host cell by inducing polymerisation of actin at one end of the bacteria giving it a “rocket tail”
Cause of variation in the genomes of pathogens
Bacteria genomes have core genes and accessory genes. These accessory genes are extremely variable and thus produce a very wide gene repertoire.
Method of transfer of genetic information between bacteria
Horizontal transmission
The 3 types of horizontal transmission
Transformation
Transduction
Conjugation
Process of transfer of genetic material between bacteria via transformation
Bacterial cell takes up free exogenous DNA from extracellular fluid and is integrated into chromosome by homologous recombination
Process of transfer of genetic material between bacteria via transduction
- Phage replicates its DNA in the bacterium and cuts bacterial DNA into small pieces
- Phages replicate and package bacterial DNA into its head
- Phage infects another bacteria and injects previous bacterial DNA which may be then incorporated into the new host’s genome
Process of transfer of genetic material between bacteria via conjugation
Transfer of plasmids through conjugative mating bridge.
- Mating bridge forms between the two
- Plasmid shared between both bacteria
- Each bacteria synthesises a new complementary strand to the plasmid
Infectivity definition
The ability of a pathogen to establish infection
Virulence definition
The degree of damage an infective pathogen can cause
Infectivity is affected by…
- Transmission to host
- Ability to colonise
- Replication
- Tropism
- Immune evasion at site of colonisation or niche
Virulence is affected by…
- Toxin production
- Enzymes that degrade host molecules
- Complete immune system evasion
- Interference with host cell function
Infective dose definition
The amount of pathogen required to cause an infection in the host
Infective dose affected by…
Combined affecting factors of infectivity and virulence
Intrinsic sources of infection
- Nasal cavity, sinuses and Upper Respiratory Tract = staph, strep
- Stomach = helicobacter pylori
- Skin = staph. epidermis
- Intestines = E.coli, clostridium species
Extrinsic sources of infection
- Secretions from mouth, nasal cavity, and upper respiratory tract = neiisseria meningitidis, strep pneumoniae
- Contaminated food and water = vibrio cholerae
- Sexual transmission = neisseria gonorrhoea, syphilis
- Nosocomial (health care workers) = staph. aureus, clostridium difficile
Portals of entry for bacteria
- Upper to lower respiratory tract = bacterial migration to lower respiratory tract, pneumococcus is normal URT flora but when it migrates downwards it becomes dangerous
- Lower GI to urogenital tract = e.coli, enterococci, candida are likely to cause UTI
- Broken skin = surgery, intravenous drug abuse, insects, pre-existing skin breaches, cuts, burns, strep pyogenes can infect wounds in the mouth
Transmission route for bacteria
- Mouth droplet transmission = strep pyogenes, meningococcal septicaemia
- Upper to lower respiratory tract = nasal sinuses, strep pneumoniae
- Inoculation through skin = staph. aureus
- Face-oral transmission = vibrio cholerae
