Microbial Mechanisms of Pathogenicity

1
Microbial Mechanisms of Pathogenicity

• chapter 15

2
definitions

• pathogenicity
• the ability to cause disease
• virulence
• the extent of pathogenicity
• many properties are unclear or unknown
• disease requires
• entry portal of entry
• adherence capsules, ligands
• avoidance penetration enzyme production
• damage toxin production

3
portals of entry exit
exit
entry
4
preferred portal of entry

• entry DOES NOT EQUAL disease
• Streptococcus pneumoniae
• if inhaled can cause pneumonia
• if enters the G.I. tract, no disease
• Salmonella typhi
• if enters the G.I. tract can cause typhoid fever
• if on skin, no disease

5
pathogen damage to host

• direct damage in the immediate vicinity
• grow multiply
• far removed from site of invasion by toxins
• spread through blood and lymph
• by hypersensitivity
• hosts reaction may cause the damage

6
numbers of invading microbes

• ID50 infectious dose for 50 of test population
• ID50 for Vibrio cholerea 108 cells
• ID50 for inhalation anthrax - lt10,000 spores
• LD50 lethal toxin dose for 50 of test
  population
• LD50 botulinum toxin 0.03 ng/kg
• 1 mg of C. botulinum toxin can kill 106 guinea
  pigs
• LD50 E. coli shiga toxin 250 ng/kg

7
pathogenicity
8
toxins

• allow spread and cause damage to the host
• contributes to pathogenicity
• toxigenicity ability to produce a toxin
• toxemia toxin in blood
• toxoid immunization
• antitoxin Ab to toxin

9
bacterial toxins
10
exotoxins

• cytotoxins
• kill cells
• neurotoxins
• interfere with normal nerve impulses
• enterotoxins
• effect the G.I. tract lining

Figure 15.5
11
hemolysins

• ?-hemolytic streptococci
• hemolysins cause incomplete lysis
• ?-hemolytic streptococci
• hemolysins cause complete lysis

12
Clostridium exotoxins

• C. tetani
• spastic paralysis

• C. botulinum
• flaccid paralysis

13
Botox Therapeutics
14
V. cholerae enterotoxin
15
endotoxins fever
Figure 15.6
16
bacteriophage-induced pathogenicity

• S. pyogenes causes strepthroat
• scarlet fever/scarlatina
• lysogenized bacteriophage codes for toxin

17
mechanisms of pathogenicity
Figure 15.9