Introduction to microbial infection Flashcards
What are Koch’s postulates
- The suspected pathogen must be present in all cases of the disease and absent from healthy animals
- The suspected pathogen must be grown in pure culture
- Cells from a pure culture of the suspected pathogen must cause disease in a healthy animal
- The suspected pathogen must be reisolated and shown to be the same as the original
Limitations to Koch’s postulates
- Difficult to grow
- Obligate parasites - cannot grow alone
- Restricted host range
- Subclinical (silent) infections
What is an infection
A disease caused by a pathogen
What is a pathogen
A microorganism that can invade the body and cause disease
What are physical barriers
Skin and mucous
What are chemical barriers
Lysozyme and sebum
What are phagocytic cells
Macrophages, monocytes, neutrophils, dendritic cells and mast cells
What is a commensal
A microorganism which forms part of the normal host microbiota
What is a pathogen
An organism/agent that causes disease
What is a pathogenesis
The development of disease
What is pathogenicity
The ability to cause disease
What is virulence
A pathogen’s power to cause severe disease
What are the factors affecting pathogenicity and virulence
- Number of infecting organisms
- Route of entry
- Immune system
- Intracellular growth and replication
- Virulence factors
What is an obligate pathogen
Almost always associated with disease
What is an opportunistic pathogen
They do not always cause disease but if given a chance can
What are the steps of infection
- Recognition
- Attachment and entry
- Multiplication
- Evasion of host defence
- Shedding and damage
How can infection be established
- 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 endogenous infection
Disease arising from a pathogen already present in the body but previously asymptomatic
What is exogenous infection
Disease arising from a pathogen not normally present in the body and comes from the environment
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
What 3 factors influence transmission
- The no. of microorganisms shed
- The number of microorganisms required to infect a fresh host
- The microorganisms stability in the environment
What is fomite transmission
Transmission via inanimate objects
ha
