Bacterial properties and disease Flashcards Preview

Y1 MCD Microbiology > Bacterial properties and disease > Flashcards

Flashcards in Bacterial properties and disease Deck (24)
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1

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

2

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

3

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

4

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

5

Define infectivity

The ability of a pathogen to establish an infection

6

Define virulence

The ability of a pathogen to cause disease

7

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)

8

What are the potential sources of bacteria?

Intrinsic - normally reside in body
extrinsic - enter body from external sources via portals of entry

9

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

10

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

11

How does neisseria meningitis cause disease?

Gram -ve bacteria is a respiratory endotoxin
Damages RBC/causes shock
Has a polysarccharide capsule ∴ antiphagocytic

12

How does E. coli cause disease?

Gram -ve
Contaminates food/water
Toxin enters blood stream via large intestine
causes kidney failure

13

How does Staphylococcus aureus cause disease?

Gram +ve
Respiratory transmission
Releases enzymes and toxins to cause multiple symptoms

14

What are the 5 stages of sepsis progression?

SIRS
Sepsis
Severe sepsis
Septic shock
MODS

15

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

16

Explain the pathophysiology of sepsis

SIRS + infection
Caused by immune and vascular system overreaction and dysregulation

17

What defines severe sepsis?

Sepsis + Lactic acidosis
SBP<90 or drop by 40 or more

18

What defines septic shock?

Severe sepsis and hypotension despite fluid resusitation
Poor tissue perfusion

19

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

20

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

21

What 7 individual differences play a role in susceptibility to infection?

Genetics
Microbiome
Nutrition
Social networks
Stress
Splenectomy
Immunosuppression

22

How to genetics play a role in susceptibility to infection?

Main factor is HLA/MHC
Determines which antigens are recognised

23

List 5 factors that determine infectivity

-transmission to host
-colonisation
-tropism
-replication
-evasion of immune system

24

List 4 factors that determine virulence

-toxin production
-degrading enzymes
-interruption of host cell processes
-complete immune evasion