Bacterial properties and disease Flashcards Preview

MCD - Microbiology > Bacterial properties and disease > Flashcards

Flashcards in Bacterial properties and disease Deck (29)
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1
Q

Meanings of coccus, bacillus, spirillus

A

Coccus - spherical
Bacillus - Rod-shaped
Spirillus - spiral

2
Q

Gram-negative bacteria features and colour under Gram stain

A
  • 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
3
Q

Examples of Gram-negative bacteria

A
Escherichia coli
Salmonella
Shigella
Vibrio cholerae
Neisseria
4
Q

Gram-positive bacteria features and colour under Gram stain

A
  • Cell wall has one membrane with a thick peptidoglycan layer and teichoic and lipoteichoic acid.
  • Peptidoglycan retains the dye.
  • Appear deep purple after stain
5
Q

Examples of Gram-positive bacteria

A

Staph. aureus
Strep. pneumoniae
Strep. pyogenes

6
Q

Acid-fast bacteria features and colour under Gram stain

A
  • 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
7
Q

Aerobic bacteria feature

A

Require oxygen for survival

8
Q

Anaerobic bacteria feature

A

Do not require oxygen for survival

9
Q

Bacterial life cycle stages

A
  • 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
10
Q

Extracellular bacteria examples

A

Staphylococcus
Streptococcus
Yersinia
Neisseria

11
Q

Intracellular bacteria examples

A
  • 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
12
Q

Salmonella’s techniques of motility and invasion

A
  • Uses flagellum for movement

- Possesses an injectisome which transfers virulence proteins into the host cell.

13
Q

Listeria’s techniques of motility and invasion

A
  • 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”
14
Q

Cause of variation in the genomes of pathogens

A

Bacteria genomes have core genes and accessory genes. These accessory genes are extremely variable and thus produce a very wide gene repertoire.

15
Q

Method of transfer of genetic information between bacteria

A

Horizontal transmission

16
Q

The 3 types of horizontal transmission

A

Transformation
Transduction
Conjugation

17
Q

Process of transfer of genetic material between bacteria via transformation

A

Bacterial cell takes up free exogenous DNA from extracellular fluid and is integrated into chromosome by homologous recombination

18
Q

Process of transfer of genetic material between bacteria via transduction

A
  • 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
19
Q

Process of transfer of genetic material between bacteria via conjugation

A

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
20
Q

Infectivity definition

A

The ability of a pathogen to establish infection

21
Q

Virulence definition

A

The degree of damage an infective pathogen can cause

22
Q

Infectivity is affected by…

A
  • Transmission to host
  • Ability to colonise
  • Replication
  • Tropism
  • Immune evasion at site of colonisation or niche
23
Q

Virulence is affected by…

A
  • Toxin production
  • Enzymes that degrade host molecules
  • Complete immune system evasion
  • Interference with host cell function
24
Q

Infective dose definition

A

The amount of pathogen required to cause an infection in the host

25
Q

Infective dose affected by…

A

Combined affecting factors of infectivity and virulence

26
Q

Intrinsic sources of infection

A
  • Nasal cavity, sinuses and Upper Respiratory Tract = staph, strep
  • Stomach = helicobacter pylori
  • Skin = staph. epidermis
  • Intestines = E.coli, clostridium species
27
Q

Extrinsic sources of infection

A
  • 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
28
Q

Portals of entry for bacteria

A
  • 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
29
Q

Transmission route for bacteria

A
  • 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