Microbial Infections Flashcards
What bacteria causes TB?
Mycobacterium tuberculosis
What are Koch’s postulates?
1- Bacteria must be present in every case of the disease
2- Bacteria must be isolated from the host with the disease and grown in pure culture
3- The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host
4- The bacteria must be recoverable from the experimentally infected host
What are two different ways in which the body resists infection?
1- Innate immune system
2- Normal flora
What does the innate immune system consist of?
1- Normal microbiota
2- Physical barriers
3- Chemical barriers
4- Phagocytic cells
There are more ____ cells than human cells in the body?
Prokaryotic
What is normal microbiota?
1- An ecological community of microorganisms- both ‘good’ and ‘bad’- present on or in the body
2- These offer protection by competing with pathogens for colonisation sites
3- Produce either antibiotic substances called bacteriocins or toxic metabolix substances to suppress growth of competing organisms
4- May alter pH (e.g. Lactobacilli)
5- Can be suppressed by antibiotics
What are the physical barriers of the immune system?
1- Skin: secretes sebum and fatty acids to inhibit growth of pathogens, however some microbes have evolved mechanisms to help them penetrate the skin
2- Mucomuciliary clearance: particles settle/are trapped on sticky mucus of respiratory epithelium, debris is transported by cilia to oropharynx where it is swallowed
3- Flushing: urinary tract, bacteria is flushed out
4- Peristalsis: GI tract, helps remove infective agents
What are the chemical barriers of the immune system?
1- Mucus: traps infective agents
2- Antimicrobial proteins: e.g. lysozyme, lactoferrin, defensins
3- Gastric acid: low pH helps destroy harmful pathogens
4- Plasma proteins: complement, C-reactive protein (CRP), Mannose-binding lectin (MBL), transferrin
What is phagocytosis?
1- Ingestion of foreign cell
2- Process used by the human body to destroy dead or foreign cells
What are the five different types of phagocytes?
1- Macrophages 2- Neutrophils 3- Monocytes 4- Dendritic cells 5- Mast cells
When does an infection occur?
When a micro-organism causes ill health
In what two ways can infection occur?
1- Invading host tissue
2- Exerting effect from mucosal surfaces
Define commensal
1- A micro-organism which forms part of the normal host microbiota
2- Benefits from others without affecting them
Define pathogen
A micro-organism capable of causing infection
Define pathogenicity
The capacity to cause disease
Define virulence
1- Measure of the capacity to cause disease
2- Degree of pathogenicity
What are the three types of pathogens?
1- Obligate pathogen
2- Conditional pathogen
3- Opportunistic pathogen
What is an obligate pathogen?
1- A type of pathogen that is almost always associated with disease
2- E.g. HIV
What is a conditional pathogen?
1- A pathogen which may cause disease if certain conditions are met
2- E.g. Bacteroides fragilis, Staphylococcus aureus
What is an opportunistic pathogen?
1- A pathogen which usually only infects an immunocompromised host
2- E.g. Pneumocytis jiroveci
What are the six steps of infection?
1- Recognition 2- Attachment and entry 3- Multiplication 4- Evasion of host defences 5- Shedding 6- Damage
How can an otherwise healthy host be infected?
1- Microbes with specific mechanisms for attachment and penetration of host’s body surfaces
2- Microbes introduced into host by anthropods (e.g. insects) that bite
3- Microbes introduced into host via skin wounds or animal bites
4- Microbes which are able to infect only when host is immunocompromised or their defences are impaired
Waht is tissue tropism?
1- The affinity for a specific tissue
2- This defines the cells and tissues of a host which support the growth of a particular microbe
3- Some microbes have broad tissue tropism, affecting many different types of tissue
4- Others may infect a certain type of tissue
5- Influencing factors include: presence of cell receptors, transcription factors, local temperature, physical defences, efficiency of barriers, and pH levels.
