EMS Microbiology Flashcards
What are Koch’s Postulates?
Causative organism must be isolated from every sufferer
Organism must be cultivated in pure culture
Typical symptoms must result in an individual inoculated
Organism must be recoverable from individuals infected
What are koch’s postulates for genes?
The gene encoding the trait of interest should be present and transcribed/translated in a virulent strain
The gene encoding the trait should not be present or should be silent in a strain that does not cause disease
Disruption of the gene should result in the formation of a strain that is incapable of causing disease
Introduction of the gene into a strain that did not cause disease should make it cause disease
Gene must be expressed in infection
What are some problems with Koch’s postulates?
Difficulty to isolate organisms
Ethical obligations
Animal models may be sufficient
What are some characteristics of viruses?
Intracellular parasites
Nucleic acid core wrapped in a protein coat made of capsomeres
Some have an envelope
Retroviruses are unusual
What are some characteristics of microfungi?
Eukaryotic Cell wall made up of chitin Hairy growths are moulds Moulds have tiny filaments known as hyphae that form mycelia Mycelia subdivided by septa
What are the 4 classes of protozoa?
Apicomplexa
Flagellate Protista
Ciliate protista
Amoeba
Name some infections caused by protozoa?
Toxoplasmosis
Amoebic Meningitis
Malaria
Amoebic dysentery
What is mutualism?
Both organisms, in a symbiotic relationship, benefit
What is neutralism?
Neither organism, in a symbiotic relationship, derives benefit or harm
What is commensalism?
In a symbiotic relationship, one organism benefits and the other derives neither benefit nor harm
What is parasitism?
One organism, in a symbiotic relationship, benefits at the expense of the host
What is the difference between sterile and non sterile sites?
Sterile sites have no normal flora
How is sterility maintained?
Surface cleaning
Barriers that allow unidirectional flow
Physical separation from non sterile sites
What are some examples of sterile sites?
Lower RT Upper GT Spinal cord Meninges Middle Ear Urinary Tract
Coagulase Negative Staphylococci
Staphylococcus aureus
Propionibacterium acnes
Corynebacterium spp
Are examples of what?
Normal skin flora
Why is the skin difficult to colonise?
Variable temp
Dry
Aerobic environment
Nutrient Poor
Viridians
Oral strep
Anaerobes gram -ve and +ve
Candida spp
Are examples of what?
Normal mouth flora
Why are cavities in the mouth easy to colonise?
Constant temp
Moist
Rich nutrient source
Few physical challenges
What organisms make up the normal nasopharyngeal flora?
Same as skin flora
What organisms make up the normal flora of the pharynx?
S. pyogenes H. influenza S. pneumonia N. meningitides S. aureus M. catarhallis
When does the flora of the vagina change?
Puberty
Addition of Lactobacillus spp to the normal skin flora
What does lactobacillus spp do?
Ferment glycogen and maintain a pH of around 3
What is the make up of flora in the stomach?
Low pH inhibits bacterial growth
Acid tolerant lactobacilli
H. pylori
What happens to the amount of organisms as you descend through the GI?
They increase in number
What are some characteristics of the flora of the large intestine?
Mostly anaerobes
Some aerobic bacteria such as enteric gram -ve bacilli
Milleri spp. also present
What are the benefits of normal flora?
Synthesis and excretion of vitamins
Colonisation resistance
Induction of cross reactive antibodies
Define pathogenicity
The capacity of an organism to cause infection
What key factors does an organism require in order to cause an infection?
Transmissibility
Establishment in or on a host
Harmful effects
Persistence
What are the 6 stages of infection?
Pathogenic organism Reservoir Exit Transmission Entry Susceptible host
What is virulence?
The degree to which an organism can cause disease
What is infectivity?
The ability of an organism to become established on or in a host via a microbial ligand or host cell receptor
What is the virulence factor for bacteria?
Endotoxins
What are some characteristics of endotoxins?
Components of the gram negative cell wall
Released from damaged/dead cells
Active component is lipopolysaccharide
Induce a range of uncontrolled host cell responses after binding to host cell receptors
What is the host response to endotoxins?
Systemic inflammatory response Uncontrolled T Lymph response Cytokine release DIC Cardiac and renal failure
Botulism is a type of which virulence factor?
Exotoxin
What is the mechanism of action of Clostridium botulinum?
Blocks ACh receptor and release of ACh causing a neuromuscular blocking effect
What is the clinical presentation of botulism?
Diplopia Dysphagia Dysarthria Dry mouth Death due to respiratory failure
What exotoxin is produced in tetanus?
tetanospasmin
What is the mechanism of action in tetanus?
Tetanospasmin binds to nerve synapses and inhibits the release of inhibitory neurotransmitters in the CNS causing a loss of inhibitory action on motor and autonomic neurons
Cholera, diphtheria, C.diff, whooping cough - are all examples of what?
Exotoxin mediated infections
Which virulence factors cause the following?
Break down of connective tissue
Inactivation of complement component C5a
Lyse blood cells
Hyaluronidase and streptokinase
C5a peptidase
Streptolycin -O and -H
How does S. progenies evade the immune system?
M-protein binds fibrinogen and masks the bacterial surface which blocks complement binding and opsonisation
This organism has a polysaccharide capsule which inhibits opsonisation and therefore phagocytosis
S.Pneumonia
