Infection (3) Flashcards
What are Koch’s postulates?
4 criteria for proving the pathogen-disease link
1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
- Microorganism must be isolated from a diseased organism and grown in culture
- Cultured microorganism should cause disease when introduced into a healthy organism
- Microorganism must be re-isolated from the inoculated experimental host and be identified as identical to the original specific causative agent
What are the 5 classes of microorganisms in size order
Viruses 20nm-1uM Bacteria 1-10uM Fungi 5-10uM Protoza 10-100uM Prions 10nm
How do bacteria differ from human cells?
Human cells have a plasma membrane and no cell wall, whereas bacteria have a cytoplasmic membrane and either a peptidoglycan or lipopolysaccharide cell wall
In human cells DNA is found in the nucleus whereas bacteria have a single stranded DNA chromosome found in the cytoplasm
Human cells have many more organelles - bacteria just have ribosomes
Bacteria have a flagella and pilli on their surface
How do bacteria and viruses differ?
Viruses are smaller, they have no independent metabolism and no organelles
Bacteria have an independent metabolism and still no organelles except some ribosomes
Viruses have a simple protein coat and cell membrane from the host cell, bacteria have a cell wall which is distinct from the host organism
Viruses have RNA or DNA, bacteria have DNA single chromosome
How are bacteria classified?
Shape: coccus or bacillus (round or rod shaped)
Gram staining: positive or negative
Peptidoglycan cell walls stain purple (positive)
Lipopolysaccharide cell walls remain pink (negative)
Outline the structure of fungi
5-10uM in size
DNA as multiple chromosomes in a nucleus = eukaryotes
Independent metabolism + organelles
Cell wall which is distinct from cell membrane of host organism
Outline the structure of protozoa
10-100uM in size
DNA as multiple chromosomes in a nucleus (eukaryotes)
Independent metabolism and organelles
Cell membrane is similar to host organism
Outline the structure of prions and prion disease
10nM in size
No RNA or DNA just a protein enzyme
No independent metabolism or organelles
No protein coat, cell wall or membrane
Normal protein PrPc -> PrPsc -> accumulates = CJD/vCJD/BSE
What’s a symbiotic relationship?
Close and long term interaction between two different species (can be mutualistic, commensal, parasitic)
What’s a commensal relationship?
Symbiotic relationship between two different species where one derives some benefit and the other is unaffected
What’s colonisation?
When a microbe grows on/in another organism without causing disease
Define infection
The invasion and multiplication of microbes in an area of the body where they are not normally present
An infection may cause no symptom and be sub-clinical or it may cause varying degrees of symptoms and be clinically apparent
What’s a pathogen? Obligate pathogen? Opportunistic pathogen?
Pathogen = microorganism that is able to cause disease
Obligate pathogen = a pathogen that must cause disease in order to be transmitted from one host to another and must also infect a host in order to survive
Opportunistic pathogen = a pathogen that takes advantage of an opportunity not normally available, such as a host with a weakened immune system, altered microbiota, breached integumentary barriers
What are normal commensal bacteria called? Where are they usually found and what can disrupt them?
Gut flora / microbiota
GI tract, skin, mouth, upper airways, lower airways, genital tract
Antibiotics (cephalosporins - ceftriaxone) may also kill normal flora meaning the individual is more susceptible to infection - eg C.diff associated diarrhoea
What’s inflammation designed to do and what type of immunity is it part of?
Inflammation is the body’s response to injury
Designed to rid the body of the initial cause of injury and break down cells damaged by injury
Part of innate immunity (first line defence)
