Pathogens and the Host Flashcards
What is clinical infection characterised by?
Inflammation
Pain
Pyrexia (raised body temperature)
Tachycardia (increased heartrate)
Rigors (sudden feeling of cold with shivers)
Increased white cell count
Increased C reactive protein (CRP)
What is pyrexia?
Raised body temperature
What is tachycardia?
Increased heartrate
What are rigors?
Sudden feeling of cold with shivers
What is a pathogen?
An organism that can cause disease
What is a commensal?
An organism which is part of normal flora
What are examples of commensals?
E coli in the gut
Staph aureus in the nose
What is a skin commensal?
Coagulase-negative staphyloccii
When can coagulase-negative staphyloccii be pathogenic?
In the presence of foreign bodies (such as prosthetic heart valves)
What is Koch’s postulates?
The criteria used to identify the agent of a particular disease
What are the principles of Koch’s postulates?
Organism must be found in all cases of the disease
Able to be cultured outside the body for several generations
Should reproduce the disease on inoculation (vaccination)
What do non-sterile sites contain that sterile sites do not?
Commensals
What do we need knowledge of to determine if something is a pathogen?
Normal flora for the site
Organisms pathogenicity
Clinical context
What is pathogenicity?
Ability of an organism to cause disease
What is flora?
Collective bacteria and other microorganisms in an ecosystem
What does an organism need to be to cause an infection?
Infectivity (ability to become established)
Virulence (ability to cause harmful effects once established)
What is infectivity?
Ability to become established
What is virulence?
Ability to cause harmful effects once established
What are things that help infectivity?
Attachment (such as P-fimbriae on E coli)
Acid resistance (such as urease on helicobacter pylori)
What is an example of attachment helping infectivity?
P-fimbriae on E coli
What is an example of acid resistance helping infectivity?
Urease on helicobacter pylori
What is urease?
An enzyme that catalysis urea to ammonia and carbon dioxide
What is virulence supported by?
Invasiveness
Toxin production
Evasion of immune system
What is virulence specific to?
Strains, not species
What is an example of invasiveness?
Streptococcus pyogenes causing:
Necrotising fascilitis (flesh eating disease)
Cellulitis
Connective tissue breakdown
Fibrinolysis
What is haemolysis?
The rupture or destruction of red blood cells
What are the 3 types of haemolysis?
Alpha haemolytic (partial haemolysis, turns blood agar green)
Beta haemolytic (complete haemolysis, turns blood agar clear)
Non haemolytic
What is alpha haemolytic?
Partial haemolysis
What colour does alpha haemolytic turn blood agar?
Green
What is beta haemolytic?
Complete haemolysis
What colour does beta haemolytic turn blood agar?
Clear
What may different species of strepococci be?
Alpha, beta or non haemolytic
What is an example of an alpha haemolytic streptococci and what does it cause?
Streptococcus pneumoniae which causes:
Pneumonia
Meningitis
Septicaemia
What are beta haemolytic bacteria further identified by?
Lancefield groupings
What are lancefield groupings based on?
Surface antigens
What groups are in lancefield groupins?
A to G
What are the clinically most important lancefield groups?
A, B and D
What is a major group A beta haemolytic streptococci and what does it cause?
Streptococcus pyogenes which causes:
Sore throats
Cellulitis
Necrotising fascilitis
What is a toxin?
A poison that acts as an antigen in the body
What are the 3 kinds of toxins?
Exotoxins (released extracellularly)
Enterotoxins (exotoxins which act on the GI tract)
Endotoxins (structurally part of the gram negative cell wall)
What are exotoxins?
Toxins that are released extracellularly
What are enterotoxins?
Exotoxins that act on the GI tract
What are endotoxins?
Toxins that are structurally part of the gram negative cell wall
What does clostridium tetani produce?
Toxins that cause tetanus
What is tetanus?
Uncontrolled muscle spasm due to loss of inhibition at the neuromuscular junction
What is used for the immunisation of tetanus?
Antigenically modified toxin
What is a toxoid?
A chemically modified toxin that is no longer toxic but is still antigenic and can be used as a vaccine
What are examples of bacteria that produce toxins?
Clostridium tetani
Clostridium perfringes
Clostridium difficile
What does vibrio cholerae cause?
Uses enterotoxins to colonise in the small intestine and cause:
Increases cAMP levels (inhibits uptake of Na and Cl ions, and secretion of Cl and HCO3 ions)
Passive outflow of water
Cause of death by dehydration
What are superantigens?
Class of antigen that cause non-specific activation of T cells resulting in massive cytokine release causing toxic shock
What are superantigens produced by?
Certain exotoxins of strep pyogenes and staph aureus
What do endotoxins cause?
Severe uncontrolled host response such as:
Cytokine production
Fever
Rigors
Hypotension
Collapse
What are examples of gram negative cocci?
Neisseria spp
Moraxella catarrhalis
E coli
What is the name of E coli?
Escherichia coli
What kinds of reserves does E coli have?
Human and animal reservoirs
What virulence machanisms does E coli have?
Pili
Capsule
Endotoxins
Exotoxins
What does E coli do?
Ferments lactose
What is a serotype?
Serologically distinguishable strain
How many serotypes of E coli are there?
Over 160
What are different kinds of virus pathogenic mechanisms?
Cell destruction following virus infection
Virus induced changes to cellular gene expression
Immunopathogenic disease
What are different kinds of virus infections?
Acute infections
Latent infections
Chronic infections
Tumour virus infections
What is an example of virus pathogenisis?
The transmission of influenza A:
1) Virus infects cells of the respiratory tract
2) Destruction of respiratory epithelium
3) Secondary bacterial infection
4) Altered cytokine expression leading to fever
Viru
What can the generation of novel influenza be caused by?
Antigenic drift (minor changes, natural mutations in the genes of flu viruses over time)
Antigenic shift (abrupt major changes in virus antigenic structure)
What is antigenic drift?
Minor changes, natural mutations, in the genes of flu viruses over time
What is antigenic shift?
Abrupt major changes in the virus antigenic structure
What are enteroviruses?
Single stranded sense RNA viruses
What are examples of enteroviruses?
Poliovirus
Coxsackie B viruses
What are some conditions caused by enteroviruses?
Poliomyelitis (caused by poliovirus)
Aseptic meningitis
Myocarditis (caused bu coxsackie B virus)
Pancreatitis (caused by coxsackie B virus)
Respiratory infections
What is viraemia?
The presence of viruses in the blood
What can viruses do from the blood?
Infect neuronal tissues which will cause paralysis
What is paralysis?
Loss of muscle function in part of your body
What is a latent virus infection?
Virus that lies dormant in a cell and can start expressing genes in the future (reactivation)
What is an example of a latent virus infection?
Herpes simplex virus
What are the 2 types of herpes simplex virus?
Cold sores (type 1)
Genetial lesions (type 2)
What is the pathogenisis of herpes virus infections?
1) Primary infection on epithelial cells
2) Virus migration to the ganglia
3) Virus reamins latent in nucleus (no virus replication)
4) Stimuli causes reactivation of the virus
5) Virus migration to epithelial cells leading to virus replication
What are examples of viruses that can induce tumours?
Papilomaviruses (cervical carinoma)
Reteroviruses (lymphomas and leukaemias)
What is the pathogenisis of human T-lymphotropic virus-1?
1) Transmission by blood and mother to child
2) Infects T cells
3) Modifies host cell gene expression using transactivating proteins (ones that cause transactivation, increased rate of gene expression)
4) Causes a variety of disease such as leukaemia
5) Directly responsible for the tumour
What are the 2 kinds of host defence mechanisms?
Innate immunity
Acquired immunity
What is innate immunity?
The non-specific first line of defence
What is responsible for innate immunity?
Physical barriers such as the skin, gastric acid and mucus
Phagocytic cells that ingest foreign bodies (such as polymorphs and macrophages)
What are different kinds of polymorphs?
Neutrophils
Eosinophils
Basophils
What is opsonisation?
Immune process where particles are targeted for destruction by a phagocyte
What is the process of optimisation?
1) Organism coated with antibody or compliment
2) Phagocyte has receptors for both and targets them
3) Efficiency of phagocytosis has improved
What is acquired immunity?
A specific immune response to the antigen concerned and an immunological memory is created
What is acquired immunity composed of?
Humoral (antibodies)
Cellular (T cells)
What does humoral mean?
Relating to body fluids
What is each organism a mix of? And what is this a mix of?
Each organism is a mix of antigens, and each antigen is a mix of epitopes
What is an epitope?
Part of an antigen which an antbody attaches itself
What is an antibody?
Y shaped protein used to neutralise pathogens, also known as immunoglobin
What is an antibody also known as?
Immunoglobulin
What are different kinds of antibodies?
Immunoglobulin M (primary response)
Immunoglobulin G (secondary response)
Immunoglobulin A (mucosal immunity)
Immunoglobulin E (allergy and helminth infections)
What do B cells do when they recognise a specific epitope?
Differentiate into a plasma cell
What is the differentiation of B cells into plasma cells initiated by?
Helper T cell
What is a monoclonal antibody?
Specificity for a single epitope
What is a polyclonal antibody?
Multiple specificity
What is a plasma cell?
Fully differentiated B lymphocyte which produces a single type of antibody
What does the compliment system form?
A cascade of 20 proteins
What is the compliment system triggered by?
The combination of an antigen and its antigen trigger
What are some functions of antibodies in infection?
Neutralising bacterial toxins
Neutralising viruses
Prevents adherance of microorganisms
Opsonises capsulated organisms
Useful means of diagnosis (serology)
What does opsonises mean?
Makes more susceptible to the action of phagocytes
What are functions of compliment proteins in infection?
Opsonisation
Lysis of gram negative organisms
Attracts polymorphs
What is lysis?
Degradation of a cell by rupture of th cell wall or membrane
Where does the humoral response happen?
Extracellularly
When is humoral immunity mostly used?
In bacterial infection, causing acute inflammation
What does humoral immunity cause?
Acute inflammation
What is cell mediated immunity?
Immune response that does not involve antibodies but the activation of phagocytes and cytotoxic T cells and the release of various cytokines
What is the process of cell mediated immunity?
1) Macrophages present antigen and stimulate T cells
2) Cytokines are produced and control the response
3) Th1 cells activate macrophages to ingest and kill pathogens
4) Cytotoxic T cells kill infected host cells or foreign cells
What are the 2 kinds of active immunisation?
Natural (exposure/infection)
Artificial (vaccination)
What are different kinds of vaccines?
Live attenuated
Killed, inactivated
Toxoid, modified toxin
What are common vaccines for travellers?
Hepatitis A
Typhoid
Yellow fever
Rabies
