Microbial Infection Flashcards
What are Koch’s Postulates?
+ The bacteria must be present in every case of disease
+ The bacteria must be isolated from the host with the disease and grown in pure culture
+ The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
+ The bacteria must be recoverable from the experimentally infected host
What does the innate immune system consist of?
+ Normal macrobiota
+ Physical barriers
+ Chemical barriers
+ Phagocytic Cells
What are features of normal microbiota?
+ More prokaryotic cells than human cells in the body
+ Offers protection by competing with pathogens for colonisation sites
+ Produce antibiotic substances suppressing growth of competing organisms (bacteriocins)
+ May produce toxic metabolic products to inhibit other micro-organisms
+ May alter pH e.g Lactobacilli
+ Suppressed by antibiotics
What are the physical barriers of the body?
+ Skin
+ Mucomuciliary clearance
+ Flushing (urinary tract)
+ Peristalsis (GI tract)
What are the features of skin as a physical barrier?
+ Secretes sebum and fatty acids to inhibit growth
+ Microbes have evolved mechanisms to penetrate skin
What are the features of mucomuciliary clearance as a physical barrier?
+ Particles settle on sticky mucus of respiratory epithelium
+ Debris transported by cilia to oropharynx where it is swallowed
What are some of the chemical barriers within the body?
+ Mucus
+ Antimicrobial proteins
- lysozyme
- lacroferrin
- defensins
+ Gastric acid
+ Plasma proteins
- complement
- C-reactive protein
- Mannise-binding lectin (MBL)
- transferrin
Name different types of phagocytes
\+ Macrophages \+ Neutrophils \+ Monocytes \+ Dendritic cells \+ Mast cells
What are the two ways that a micro-organism can an cause infection by causing ill-health?
+ Invading host tissues
+ Exerting effects from mucosal surfaces
What is a commensal?
A micro-organism which forms part of the normal host microbiota
What is a pathogen?
A micro-organism capable of causing an infection
What is pathogenicity?
The capacity to cause disease
What is virulence?
Measure of the capacity to cause disease i.e degree of pathogenicity
What are the different types of pathogens?
+ Obligate
+ Conditional
+ Opportunistic
What is an obligate pathogen?
+ Almost always associated with disease
+ E.g HIV
What is a conditional pathogen?
+ May cause disease of certain conditions are met
+ E.g Bacteroides fragilis, Staphylococcus aureus
What is an opportunistic pathogen?
+ Usually only infects immunocompromised hosts
+ E.g Pneumocystis jiroveci
What are the steps of infection?
> Recognition > Attachment & entry > Multiplication > Evasion of host defences > Shedding > Damage
What are ways that infection can be established in normally healthy hosts?
+ Microbes with specific mechanisms for attachment and penetration of host’s body surfaces
+ Microbes introduced into host by biting arthropods
+ Microbes introduced into host via skin wounds or animal bites
+ Microbes able to infect only when host defences are impaired
What is tissue tropism?
+ Affinity for a specific tissue
+ Defines the cells and tissues of a host which support the growth of a particular microbe
+ Some microbes have a broad tissue tropism, infecting many types of cells and tissues
+ Others may primarily infect a single tissue
What are factors that may influence tissue tropism?
\+ Presence of cell receptors \+ Transcription factors \+ Local temperature \+ Physical barriers \+ pH
What microbe targets nerve cells?
Varicella zoster virus (VZV)
What microbe targets the upper respiratory tract?
Rhinovirus
What microbe targets the liver cells?
Hepatitis B virus (HBV)
