C6 Flashcards
(27 cards)
How bacteria become antibiotics resistance
Under selective pressure
Define selective pressure
Evolutionary force that cause particular phenotype to be more favourable in certain environmental conditions
Explain selective pressure
- Must have at least 2 possible phenotype that organism exhibit
- If there’s environmental influence that cause selective pressure & favouring 1 phenotype
- That phenotype will be more abundant in population
Example of selective pressure
- Environmental condition
- Availability of food & energy sources
- Predators
- Disease
- Human influence
Mechanism where microbes produce genetic variability
- Point mutation
- Genetic arrangement: meiosis
- Gene transfer
Explain point mutation
- Occur randomly
- Due to replication error/ incorrect repair
- Can be silent or result in modified protein
- Slow process evolution
Explain genetic rearrangement
- Rearranging part of genome
- Result in amplification of specific gene product
- Result in loss of part of genome that no longer essential
Explain gene transfer
- Transfer new genetic trait from other organism
- Occur via vertical or horizontal gene transfer
- Vertical: transfer genetic material from mother to daughter cell during cell division
- Horizontal: transfer genetic material between bacterial cell uncouple with cell division
Mechanism of horizontal gene transfer
- Transformation
- Transduction
- Conjugation
Define genomic island (GEI)
Discrete DNA segment that establish horizontally transfer gene in population
Characteristics of GEI
- Large size
- Associated with tRNA ecoding gene
- Encode housekeeping gene & rRNA
- Can excise themselves spontaneously from chromosome & transfer to recipient
- Carry bacteriophage, plasmid & insertion sequence
Importance of GEI
- Contribute to fitness & adaptations
- Provide gain of function to host
- Promote transfer of multi gene families
- Bring gene that help in bacterial survival
IPEC divided to
- EPEC
- EHEC
- ETEC
- EAEC
- EIEC
- DAEC: diffusely adherent
ExPEC divided to
- UPEC: uropathogenic
- MENEC: new born meningitis causing
- SEPEC: septicemia
- APEC: avian pathogenic
What is pathogenicity island (PAI)
Unstable region of chromosome with variable virulence associated characteristics
Explain PAI
Comparison between pathogenic bacteria & harmless one of close relative often reveal extra block of genetic material that contain gene that encode virulence factor protein or other structure to cause disease
Basic properties of PAI
- Carry many virulence gene
- Incorporated in genome of pathogenic microbes
- Cary mobility gene (transpoase, integrase)
- Unstable & prone to deletion
- Encode secretion system & adhesion, toxin
PAI flank by
- Direct repeat sequence (DR)
- tRNA
- Insertion sequence (IS)
Explain PAI & acquisition of virulence
- Creat pathogen from non pathogen strain by HGT
- Example: E.coli
- E.coli can be commensal and virulent
- Produce vitamin K & B12
Explain IPEC
EPEC
- Adhere to small bowel enterocytes
- Destroy normal microvillar
EHEC
- Attach & effacing lesion in colon
- Shiga toxin
ETEC
- Adhere to small bowel enterocytes
- Induce watery diarrhoea by heat labile & heat stable enterotoxin
EAEC
- Adhere to small & large bowel epithelia in thick biofilm
EIEC
- Invade colonic epthial cell & lyse phagosome
DAEC
- Effect small bowel enterocytes
List of acquired PAI via HGT
- PAI I: code for hemolysin
- PAI II: code for alpha hemolysin & P fimbriae
- PAI III: code for S oili & iron uptake
- PAI IV: code for iron uptake (chelator)
Pathogenicity island in E.coli
- Inner circle: nucleotide base pair
- Jagged circle: GC content
- Red region: gene present in pathogenic strain
- Green region: common to all strain
Define R0
Number of secondary infection that would result from introduction of one infectious host into population of susceptible individuals
A successful pathogen must do
- Acquire nutrient
- Survive stress
- Avoid host immune system
- Move to site of infection
