Pathogenicity Flashcards
What are the 3 important clinical elements in microbiology
- Detection
- Treatment
- Prevention
What is a pathogen?
An organism capable of causing disease
What is a commensal microorganism?
An organism that is part of the normal flora
What does the term ‘pathogenicity’ refer to?
The ability to cause disease
What does the term ‘virulence’ refer to?
The ability to cause severe disease
Describe the life cycle of a parasite
- Enter
- Attach
- Colonise
- Evade host immunity
- Produce harmful proteins
- Release from host
- Disseminate
What are the 5 classes of microorganisms?
- Viruses
- Bacteria
- Fungi
- Prions
- Parasites
What is the term used to describe when microbes find a new host and start to multiply?
Colonisation
What is an infection?
If a microbe causes disease
If the source of microbe in an infection is from the patient’s own flora, what type of infection is this?
Endogenous infection
If the source of microbe in an infection is from flora outside the patient’s body, what type of infection is this?
Exogenous infection
Which enzyme is in tears that kills bacteria?
Lysozyme
What are the 4 Koch’s Postulates (The Germ Theory of Disease)?
- The microbe must be present in every case of the disease
- The microbe must be isolated from the diseased host and grown in culture
- The disease must be reproduced when a pure culture is introduced into a susceptible host
- The microbe must be recovered from an experimentally infected host
Give examples of routes of microbial entry into host
- Ingestion
- Inhalation
- Injection
- Across mucous membranes
- Into the ear
- Transplacental
What is a problem with Koch’s postulates in determining the microorganism responsible for a specific disease?
Most diseases are polymicrobial - have lots of microorganisms associated with them
e.g. gingivitis - lots of bacteria in the oral cavity. Difficult to determine which causes gingivitis
What percentage of women develop a U.T.I in their lifetime?
50%
What is the main defence against U.T.Is?
Flushing action of urine
What is the Tamm-Horsfall protein?
A protein in humans that binds specific E. Coli strains. Protects against U.T.Is
What are UPECs?
UroPathogenic Escherichia Coli - a stain of E. Coli that cause most (90%) urinary tract infections
Give some examples of encapsulated infections
Meningitis, pneumonia, otitis media and sinusitis
Give some examples of encapsulated bacteria
Streptococcus pneumoniae, Haemophilus influenza, Neisseria meningitidis, Group B Streptococcus
What are the functions of the bacterial capsule?
- Mediate adhesion
- Immune system evasion
- Protects from desiccation
- Reserves of carbohydrate
What is an endotoxin?
- LPS - lipopolysaccharide
- On Gram - bacteria
- Part of the outer portion of the cell wall
- Induce the immune response
What is an exotoxin?
- A toxin released by bacteria into the surrounding environment
- Produced mostly inside Gram + bacteria
- Secreted following lysis
Describe how endotoxin shock can happen during elective surgery
- Contents of gut perforated
- Gram - bacteria enter the bloodstream
- LPS mediate mast cells, neutrophils, macrophages
- Endothelium of blood vessels dilate
- Fever
- Vascular permeability
- Vascular hypertension
- Causes shock
What is the most lethal toxin in the world?
Botulinum
Which bacterium produces botulinum?
Clostridium botulinum
What does botulinum cause?
- Flaccid paralysis
- Stops nerve conduction by blocking acetylcholine transmission
What effect does tetanus have on the body?
- Overacts nerve endings
- Leads to painful muscle contractions /uncontrolled muscle spasms
Which bacterium produces tetanus?
Clostridium tetanus
Which are more potent: endotoxins or exotoxins?
Exotoxins are more potent
They are more specific
