C6 Flashcards
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
Define antibiotic prophylaxis
Use of antibiotics before surgery to prevent bacterial infection
Criteria to use antibiotic prophylaxis
- Use not to treat but prevent
- Prevent normal commensal microbe from spreading their usual site
- Must meet certain criteria before use
- Must use at short time to avoid resistance
- Suitable conc must be used at the right time
What is selective pressure for bacteria, parasites, virus, fungi & animals
- Immune systems
- Pathogen have phenotype that increase resistant to immune defence are likely to replicate & infect other host
