bacterial pathogensis Flashcards
What are pathogens
Disease casing bacteria affecting all with normal host defences
What are non-pathogenic pathogens
Organisms that invade an individual without causing any obvious detectable symptoms
What are asymptomatic infections caused by
Microbes
Till when can organisms remain latent (dormant/inactive form)
Until they are reactivated with the recurrence of symptoms
What are the 3 consequences of antibiotic use in the alteration of normal gut flora
Sensitive gut flora killed => overgrowth with resistance => C. Difficile toxin production => diarrhoea and pseudomembranous colitis
What are the treatment options for affected normal gut flora from the use of antibiotics
-stop prescribing antibiotic
-oral metronidazole or vancomycin
-recovery requires reestablishment of normal flora
What is the first Koch’s postulates
1)the pathogen must be present in every case of the disease
What is the second Koch’s postulates
2)the pathogen must be isolated from the diseased host and grown in a pure culture
What is the third Koch’s postulates
3)the specific disease must be reproduced when a pure culture of the pathogen is inoculated into a healthy susceptible host
What is the fourth Koch’s postulates
4)the pathogen must be recoverable from the experimentally infected host
What are methods for the transmission of pathogens
Oral - oral
Feces - oral
Blood - blood
Sexual - contact
How is iron fundamental in infection
Without iron bacteria cannot power themselves to be pathogenic
What are 7 microbial pathogenicity factors
-toxins
-iron uptake
-adhesions
-LPS
-invasins
-slime
-enzymes
When does the first invasion occur for commensal microbes
When they breach the mucosal layer and eating + using nutrients from cells to produce factors and allow for pathogenicity
What are characteristics of flagellae
-multi-subunit structures
-mono or poly-trichous
How does flagellae help in reaching site of infection
Facilitates propulsion (propelling) to specific host targets
What is flagellae recognised by
By the innate immune system as PAMP recognised by TLR5
What are characteristics of frimbriae
-hair like surface structures
-consist of various protein subunits
What are the types of bacterial adhesion
-flagellae of gram-negative bacteria
-fimbriae and pili of gram-negative bacteria
What do fimbriae interact with
Eukaryotic cells or inert surfaces via receptors at the tip
What do many fimbriae receptors recognise
Sugars
What are characteristics of pili
-structurally similar to fimbriae
-longer than fimbriae
-mostly only one present on surface
What are pili involved in
In the conjugation (f-pili) or serve as receptors for phages
Why is adhesion important for bacteria to host cells
-prevents bacteria from being washed off by fluid flow
-formation of a micro colony
-relevance to pathogenicity
What do adhesins cause
Bacteria adhesion to host cell, formation of colonies and biofilms
What do toxins do
Cause the destruction of tissue
What do invasins do
Invasion and multiplication of bacteria
What are the different type of toxins produced from bacteria
Exotoxins
Endotoxin
Enterotoxin
What are exotoxins
Any toxin that is actively secreted by a bacterium in the environment or supernatant
What is an endotoxin
A synonym for the LPS of gram-negative bacteria - only associated with gram -ive bacteria (cell-surface bound)
What is an enterotoxin
An exotoxin that is effective in the gastrointestinal tract
What is the mode of action of botulinum toxin (Botox toxin) (exotoxins)
-botulinum toxin acts at the end of motor end plate to prevent release of acetylcholine from vesicles
-results in lack of stimulus to muscle fibres
-irreversible relaxation of muscle and flaccid paralysis
What is the mode of action of tetanus toxin (exotoxins)
-tetanus toxin binds to interneuron to prevent release of glycine from vesicles
-result in lack of inhibitory signals to motor neurons
-constant release of acetylcholine to muscle fibres
-irreversible contraction of muscles and spastic paralysis
What are invasin factors
Protease
Glycosidases
Nucleases
Lipases
How do the invasive factors lytic toxins damage membranes enzymatically and physically
Enzymatically - phospholipases
Physical - membrane-insertion
How do invasins cause damage enzymatically
Produced as enzymes and degrade enzymatic pathways
How do invasins cause damage physically
Invasins physically inserted into eukaryotic cell membranes to then bind to cholesterol or non-cholesterol structures
What produces iron binding compounds
Siderophores
What does a greater production of sidephores result in
The microbe being more virulent and pathogenic
What are defensive pathogenic factors from the host defence mechanism
-polysaccharide capsule:negatively charged
-slime
-biofilm
What are defensive pathogenic factors from the host immunogenic mechanism
-LPS:cytokines overstimulation -> leads to septic shock
-outer membrane proteins (OMPs): inactivate anti microbial peptides or complement factors
