Infection 1-6 Flashcards
What are the 4 steps of the Koch Henle Postulates?
- Isolate the organism from every case
- Propagate in pure culture in vitro
- Re-inoculate and produce disease
- Re-isolate
What are the key differences between Koch’s postulates and diagnosis?
Koch’s - Isolates SAME organism from MANY patients and isolates able to reproduce disease in model
Diagnosis - ONE isolate from ONE patient. Identify if the organism is a recognised pathogen.
How can microbes be classified biologically?
Prokaryote
Eukaryote
Viruses
How can microbes be classified medically?
Pathogen
Non-pathogen
Opportunistic pathogen
What are the main differences between eukaryotes and prokaryotes?
Eukaryotes have membrane bound organeles and multiple chromosomes. Prokaryotes only have one and transcription/translation is coupled (compartmentalised in eu.). Ribosomes - 30+50S=70S pro. 40+60S=80S eu.
How do viruses infect the host?
Obligate intracellular parasites that multiply using the host cell’s biosynthetic machinery.
What is a bacteriophage?
Virus which infects bacteria
What are the principle characteristics of innate immunity?
Rapid response
Invariant
Limited number of specificities
Constant during response
What are the principle characteristics of adaptive immunity?
Slow response
Variable
Numerous highly selective specificities
Improve during response
How do neutrophils act?
Phagocytosis and killing of microorganisms. Granules contain numerous bactericidal substances.
Phagocytosis particles opsonised by IgG or compliment and functions as effector cell of humoral immunity
How do eosinophils act?
Killing of antibody-coated parasites through release of granule contents - highly basic or ‘cationic’ proteins
Bind avidly to IgE-coated particles
Describe the nucleus of a neutrophil (polymorph)
multilobed
What type of white blood cells are common at the site of an allergic reaction?
Basophils and eosinophils
What is a basophil and how does it work?
A leucocyte with large basophilic granules which contain heparin, histamine and other vasoactive amines. Granules released at the site of inflammation and in immediate hypersensitivity (allergic) reactions
Express high affinity receptors for IgE - interaction causes the release of basophil granules
What is a mast cell?
A tissue cell which is not bone marrow derived but otherwise similar to its circulating counterpart, the basophil
What is the largest nucleated cell of the blood?
Monocyte - 16-20 micrometers.
What is a macrophage?
Antigen presenting cell
Mature monocytes
Strongly phagocytic
Receptors for Ig and complement
What are natural killer cells?
Type of lymphocyte able to kill virus infected cells and certain types of cancer cells
Large cytoplasmic granules distinguish them microscopically
How do NK cells and cytotoxic T cells act differently?
NK act independently of antigen presentation and recognition, which is necessary for the action of T cells
What are dendritic cells?
Antigen presenting cells. Possess long processes which interdigitate between lymphoid cells and interdigitate between lymphoid cells and present antigens to them.
What is a B lymphocyte and where is it derived?
Precursor of antibody-forming cells. Bone marrow derived
What is a plasma cell?
The B lymphocite in its high-rate antibody secreting state. Rarely seen in the blood, but found in spleen, lymph nodes etc whenever antibody is being made.
From where are T lymphocytes derived?
Thymus
What are the primary lymphoid organs?
Bone marrow where T and B lymphocytes are made. Thymus where T lymphocytes mature/are selected
What are the secondary lymphoid organs?
Eg. Spleen, lymph nodes nad peyers patches. Contain T cells, B cells, antigen presenting cells
What cells constitute the bone marrow stroma?
Fibroblasts (reticular connective tissue) Macrophages Adipocytes Osteoblasts Osteoclasts Endothelial cells forming the sinusoids
What are the 3 types of stem cells present in bone marrow?
Haematopoietic - wbc, rbc and platelets
Mesenchymal - gatekeeper cells of marrow
Endothelial stem cells
What is aplastic anaemia?
Bone marrow does not produce sufficient new cells to replenish blood cells. Deficient in all blood cell types.
Idiopathic or autoimmune - wbc attack bone marrow
Describe the development of T cells.
Precursors arrive at thymus from bone marrow. Cortex and medulla educate thymocytes into mature competent T cells. Mature T cells are released into the peripheral.
What are thymocytes?
Precursor lymphocytes from the bone marrow which enter the thymus via blood vessels. Proliferate and mature in the thymus. 1-3% survive the selection process that allows mature T cells to enter the peripheral circulation.
Name 2 diseases associated with Thymus disease.
Severe combined Immunodeficiency - SCID
DiGeorge Syndrome - genetic disorder causesd by deletion of a small setion of chromosome 22
What type of cells are CD3,4,8,16 and 19?
CD3 T cells CD4 Helper T cells CD8 Cytoxic T cells CD16 Macrophages CD 19 B cells
Describe the path of B cells through lymph nodes.
Travel from the blood stream entering the cortex via high endothelial venules. Leave via efferent lymph.
What happens when a B cell encounters an antigen?
Forms primary foci from which proliferating cells migrate to the primary follicle forming a secondary follicle with a germinal centre. A few weeks after it forms, the germinal centre reaction dies down.
What may cause lymph nodes to enlarge?
Infection Virus Inflammation Cancer Caner of the blood
What is GALT?
Gut Associated Lymphoid Tissue
What is MALT?
Mucosa Associated Lymphoid Tissue
What is SALT?
Skin Associated Lymphoid Tissue
What are tonsils?
Mass of lymphoid tissue in submucosa of oropharynx. Many lymphoid follicles, mostly with germinal centres
What are Peyers patches?
Organised patches of lymphoid follicles int he submucosa of the gut, mainly the ileum
What is an infection?
Invasion of a host's tissues by microorganisms Disease caused by: - microbial multiplication - toxins - host response
What is microbiota?
“commensals”
Microorganisms carried on skin and mucosal surfaces
Normally harmless or even beneficial
transfer to other sites can be harmful
How may infections be spread?
Physical contact Airborne Vector may be necessary Ingestion Inhalation Mother to child - vertical transmission
What determines the disease caused by an infection?
Pathogen: - virulence factors - inoculum size - antimicrobial resistance Patient: - site of infection - co-morbidities
How do you determine if a patient has an infection?
History - symptoms/exposure
Examination
Investigations - specific/supportive
How do microorganisms cause disease?
Exposure -> adherence -> Invasion -> Multiplication -> Dissemination
What are virulence factors?
Factors of viruses that cause disease - exotoxins e.g.. cytolytic, AB toxins, Superantigens, enzymes and endotoxins
What are some supportive investigations?
Full blood count C reactive protein Blood chemistry Imaging Histopathology
Name some tests you might use to determine specific infection bacteriology.
Specimen type
M, C & S - microscopy, culture and sensitivity (antibiotic susceptibility)
Antigen detection
Nucleic acid detection
Name some tests you might use to determine specific infection virology
Antigen detection
Antibody detection
Detecting viral nucleic acid
What are the 2 semi-independent parts of the lymphatic system?
Lymphatic capillaries and vessels
Lymphoid tissues and organs
What is the function of the lymphatic system?
Fluid balance
Fat absorption
Defence
What is the lymphatic system?
A network of vessels that assist in circulating fluids - excess fluid away from interstitial spaces to the blood stream
What is the structure of lymphatic capillaries?
Tiny closed end vessels consisting of simple squamous epithelium. More permeable than blood vessels because they lack a basement membrane.
Resemble small veins, one way valves
How are lymphatic vessels compressed?
Contraction of surrounding smooth muscle
Periodic contraction of smooth muscle in lymphatic vessel wall
Pressure changes in the chest during breathing
Where does the right lymphatic duct converge and empty into?
Upper right limb and right half of head, neck and chest and empties into right subclavian vein
Where does the thoracic duct converge and empty into?
Rest of body (compared to right lymphatic duct) and empties into the left subclavian vein
What are the lymphoid organs?
Lymph nodes
Tonsils
Spleen
Thymus gland
Describe the structure of lymph nodes.
Rounded structures distributed along the lymphatic vessels
Outer part - cortex. Follicles with germinal centre (contains dividing lymphocytes)
Inner part - medulla. Contains phagocytic macrophages.
What are lacteals?
Special lymphatic vessels located in the lining of the small intestine -. fat enters lymphatic vessels and then venous circulation
What is chyle?
Lymph that is milky in appearance due to fat.
How does the lymphatic system act in the bodies defensive mechanisms?
Removes organisms and foreign substances from the lymph
Associated with activation of the immune system.
What is the collective term for lymph node enlargement?
Lymphadenopathy - may be due to lymphadenitis (painful and responding to foreign antigen) or metastatic cancer (usually painless and firm)
What is the function of tonsils?
Trap and remove bacteria and other foreign materials
How is tonsillitis caused?
Congestion of bacteria.
What is the spleen?
The largest lymphatic organ containing sinuses filled with blood. 2 tissue types - red and white pulp.
What is red pulp?
Receives arterial blood which passes into venous sinuses. Lined by macrophages - removes old red cells and recycles iron
What is white pulp?
T and B cell compartments with macrophages and other immune cells.
What is the function of white pulp?
Recognise pathogens, remove pathogens and activate T cells and B cells
How does age affect the thymus?
Largest at infancy and during puberty, small in an adult and replaced by fat and connective tissue in the elderly.
What is the function of the thymus?
Site of T lymphocyte production
Secretes protein hormones called thymosins
What are the main types of fungi?
Yeast
Mould
What are the 2 most common types of pathogenic parasites in humans?
Protozoa Helminth (worm)
How does age affect immunity?
Different antibodies at different ages - inter-uterine from mother etc
How does gender affect immunity?
Hormones
Anatomy - UTI
How do social factors affect immunity?
What you are exposed to.
How does time affect disease?
Calendar time - weather, temperature etc
Relative time - time since being somewhere (?)
How does where a patient has been affect their chances of disease?
Some diseases are more common in different countries/places and people who have visited are less likely to have immunity than those that live there. Therefore, where they currently live and have recently visited can affect their health
Name some mechanisms of infection
Contiguous spread Inoculation Haematogenous Ingestion Inhalation Vector Vertical transmission
What 3 things is a diagnosis based on?
History
Examination
Investigation
What specific treatments might be given for an infection?
Antimicrobials
Surgery - drainage, debridement, dead space removal
What supportive treatment might be given for an infection?
Symptom relief
Physiological restoration
What is a purpuric rash?
The appearance of red or purple discolouration on the skin that does not blanch on applying pressure. Looks like bleeding under the skin. 3-10 mm diameter of spots
What are the clinical features of sepsis?
Systemic inflammatory response syndrome A response to a non-specific insult Two or more of: - Temperature 38 - Heart rate >90 - Resp. rate >20/min WBC 12x10^9/L
What is bacteraemia?
Presence of bacteria in the blood
What is septicaemia?
Clinical term meaning generalised sepsis
What is sepsis?
The systemic response to infection - SIRS + documented/presumed infection
Define severe sepsis.
SIRS + organ dysfunction/hypoperfusion (hypotension, decreased urine output)
Define septic shock.
Severe sepsis + persistently low blood pressure despite administration of intravenous fluids
What is the common bacterial pathogen to cause meningococcal meningitis in a teenager and how is it spread?
Neisseria meningitidis.
Spread by direct contact with respiratory secretions. Most people are harmlessly colonised but in the unlucky few, rapidly progressive.
How is low blood pressure caused in a septic patient despite the high pulse rate?
Endotoxins that the bacteria release cause vasodilation, decreasing total peripheral resistance. Mean arterial blood pressure = Total peripheral resistance + Cardiac output
What is the role of a pilus on a bacterial cell?
Enhances attachment to other cells
What does the polysaccharide capsule on a bacterial cell do?
Promotes adherence
Prevents phagocytosis
In the inflammatory cascade, what are the local effects of cytokines?
Stimulate inflammatory response to promote wound repair and recruit RE system
In the inflammatory cascade, what are the systemic effects of cytokines?
Stimulating growth factor, macrophages and platelets. Goal is homeostasis. Lead to activation of humoral cascade and RE system
How can the release of cytokines cause organ ischaemia, dysfunction and failure?
Cytokines initiate the production of thrombin and also inhibit fibrinolysis
Coagulation cascade leads to microvascular thrombosis…
Microvascular injury is the major cause of shock and multiorgan failure
What urgent investigations would you order on someone with sepsis?
Full blood count, urea and electrolytes EDTA bottle for PCR Blood sugar Liver function test C-reactive protein Clotting studies Blood gases
What are the sepsis 6 and when must they be delivered?
Within 1 hr:
Deliver high flow oxygen
Take blood cultures and other cultures and consider source
Administer empirical IV antibiotics
Measure serum lactate
Start IV fluid resuscitation
Commence accurate urine output measurement