virulence by dr shireen rafiq (rmc)
TRANSCRIPT
BACTERIAL VIRULENCEDr Shireen Rafiq
MBBS, M.Phil, Ph.D
Koch’s PostulateKoch’s Postulateisolated isolated
diseased not healthy peoplediseased not healthy peoplegrowthgrowth
pure culturepure cultureinduce disease induce disease
susceptible animalssusceptible animalsre-isolated re-isolated
susceptible animalssusceptible animals
Normal flora
Resident ------commensals
TransientCarrier stateColonization
A pathogen is a microorganism that is able to cause disease in a plant, animal or insect.
Pathogenicity is the ability to produce disease in a host organism.
Microbes express their pathogenicity by means of their virulence=the degree of pathogenicity.
Infectious dose depends on virulence factors
ROUTES OF ENTRY
Host defensesHost defensesGutGutperistalsis peristalsis defecation defecation
respiratory tract respiratory tract ciliary action ciliary action coughingcoughingsneezingsneezing
urogenital tract urogenital tract urination urination
MICROBESPathogens Opportunistic Pathogens Obligate Pathogens Symbiosis: Mutualism Parasitism Commensalism
PEPTIDOGLYCAN
CAPSULE/BIOFILMS
PILI
FIMBRIA
LIPOTECHOIC ACID
PLASMIDS
VACUOLE FORMATION (in Host)
HYDROPHOBIC MOLECULES
TOXINS (Exotoxin and Endotoxin)ENZYMES
SIDEROPHORES (ferric ions)
STRUCTURAL
NON STRUCTURAL
ADHERENCE FACTORSAdhesin/Ligand: A surface structure or macromolecule
that binds a bacterium to a specific surface. Receptor: A complementary macromolecular binding
site on a (eucaryotic) surface that binds specific adhesins or ligands
Biofilms: protect bacteria from antibiotics and host defense resulting in chronic wound infections
Vs INFECTION
E. coli with fimbriae
Factors Facilitating PathogenesisADHESINSANTIPHAGOCYTIC FACTORS -CAPSULE -M PROTEIN -CYTOTOXINSURVIVAL WITHIN PHAGOCYTES (PREVENTION OF)
-OXID. BURST -FUSION AND DEGRANULATION -LYSOZYMES -ESCAPE FROM PHAGOSOMES SIDEROPHORESTOXINS AND ENZYMESPLASMIDS
Toxigenesis is the ability to produce toxins.
Exotoxins (gram positive and gram negative) secreted by bacteria, polypeptide
Endotoxins (gram negative ) part of cell wall, lipopolysaccharide.
A-B toxinsA-B toxins
ActiveActiveBindingBinding
AA
Cell surfaceCell surface
BB
• ProteasesProteases • PhospholipasesPhospholipases• Detergent-like actionDetergent-like action
Membrane damaging exotoxins
EXOTOXIN ENDOTOXIN1. EXCRETED INTEGRAL
2.GRAM POSITIVE AND NEGATIVE
GRAM NEGATIVE
3. POLYPEPTIDE LIPOPOLYSACCHARIDE
4. UNSTABLE/DESTROYED ABOVE 60C
STABLE ABOVE 60C
5. HIGHLY ANTIGENIC Toxoid formation
WEAKLY ANTIGENIC
6. HIGHLY TOXIC (ug) MODERATELY TOXIC (mgs)7. BIND TO RECEPTORS RECEPTORS NOT INVOLVED8. NOT PYROGENS PYROGENIC9. PLASMID OFTEN INVOLVED CHROMOSOMAL
EFFECTS OF ENDOTOXIN Lipid A
FeverShockStimulation of immune systemGreater susceptibility to stressLethality
Stages of infectious diseaseIncubation period
Prodromal period
Specific illness period
Recovery period
MUTATIONSChange in the base sequence of DNA resulting in
altered phenotype. Mutations result from three type of molecular changes
1 Base substitutions2 Frameshift mutation3 Transposons or insertion sequenceChemicals , radiations and viruses
TRANSDUCTION
RECOMBINATIONHomologous
Non homologous
different endonucleases and ligases are involved