Bacterial properties and disease Flashcards
Properties; Gene transfer; Infectivity and virulence; Sources and routes; Pathogens; Pathophysiology; SIRS; Sepsis treatment; Susceptability; Therapeutic targets
What is the difference between gram positive and gram negative bacteria?
Gram +ve stains violet -Peptidogylcan cell wall -e.g. Strep pneumoniae Gram -ve stains pink -LPS and peptidoglycan cell wall -e..g E.coli
What define acid fast bacteria?
Bacteria resistant to gram staining method due to waxy mycolic acid in cell walls
Stained with acid-fast stain method - resist decolourisation with acid alcohol
What is the difference between extracellular and intracellular pathogens?
Extracellular replicate outside of cells
Intracellular enter cells to replicate inside endo/phagosome and can survive by escape, preventing lysosome fusion, or survival in the phagolysosome
What are the 3 main ways bacteria exchange genetic material?
Transformation
-absorption and incorporation of naked DNA into host genome from surroundings
-e.g. Streptococcus
Transduction
-Basic process of viral replication
-Some bacterial DNA packaged and inserted into new bacterial genome
Conjugation
-Bridge between two bacteria used to exchange plasmids
Define infectivity
The ability of a pathogen to establish an infection
Define virulence
The ability of a pathogen to cause disease
Define infective dose
The minimum amount of a pathogen required to establish a disease
Influenced by infectivity and virulence
Measured in CFU (colony forming units)
What are the potential sources of bacteria?
Intrinsic - normally reside in body
extrinsic - enter body from external sources via portals of entry
What are 8 possible routes of infection?
Neonate and urogenital tract during birth Surgery Upper respiratory tract Urogenital tract Broken skin Gastro-intestinal tract Faeco-oral
Give 5 examples of important bacterial pathogens and their routes of transmission
Mouth - streptococcuus pyogenes, Meningiococcal septicaemia
Resp tract upper to lower - Streptococcus pneumoniae
Faeco-oral - cholera
Through skin - Staphylococcus aureus
How does neisseria meningitis cause disease?
Gram -ve bacteria is a respiratory endotoxin
Damages RBC/causes shock
Has a polysarccharide capsule ∴ antiphagocytic
How does E. coli cause disease?
Gram -ve
Contaminates food/water
Toxin enters blood stream via large intestine
causes kidney failure
How does Staphylococcus aureus cause disease?
Gram +ve
Respiratory transmission
Releases enzymes and toxins to cause multiple symptoms
What are the 5 stages of sepsis progression?
SIRS Sepsis Severe sepsis Septic shock MODS
What criteria define SIRS?
2 or more symptoms of:
- Temperature >38 or <36
- Resting HR >90
- Resting respiratory rate >20
- WBC count >10k or <4k
Explain the pathophysiology of sepsis
SIRS + infection
Caused by immune and vascular system overreaction and dysregulation
What defines severe sepsis?
Sepsis + Lactic acidosis
SBP<90 or drop by 40 or more
What defines septic shock?
Severe sepsis and hypotension despite fluid resusitation
Poor tissue perfusion
What is the pathophysiology of septic shock?
WBC release due to pathogen→chemical release→endothelial damage→increased permeability
NO release→increased permeability
Increased permeability→fluid loss→less perfusion and hypotension
CO increase to compensate low TPR
How is sepsis treated?
Early detection is key
Target infection with antibiotics and blood products
Try to increase BP to prevent shock with fluids and vasopressors
What 7 individual differences play a role in susceptibility to infection?
Genetics Microbiome Nutrition Social networks Stress Splenectomy Immunosuppression
How to genetics play a role in susceptibility to infection?
Main factor is HLA/MHC
Determines which antigens are recognised
List 5 factors that determine infectivity
- transmission to host
- colonisation
- tropism
- replication
- evasion of immune system
List 4 factors that determine virulence
- toxin production
- degrading enzymes
- interruption of host cell processes
- complete immune evasion
