Infectious Diseases - 1

  • Created by: LBCW0502
  • Created on: 08-11-19 12:18
What is infection? (1)
'The great mimic'. One organism with a wide range of clinical pictures. Different organisms with same signs and symptoms. Can resemble non-infectious conditions and vice versa. Difficult to determine precise diagnosis (need to look at symptoms/DH)
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What is infection? (2)
Interaction between organism and host. Usually peaceful and microbe may co-exist as normal flora. Can cause problems if state of host changes. Microbe may exist in environment - cause infection if it gets past host defences
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What is infection? (3)
Can be lead to abnormalities in the patient, tissue invasion/damage. Distinguish between contamination, colonisation, infection
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What is infection? (4)
Infection might get past host defences due to reduced immune response e.g. diabetes, immunosuppression (risk of infection). E.g. respiratory infection - affects epithelium, passing through damaged epithelium (staphylococcal infection)
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What is contamination?
Transient presence of microbes (able to remove presence of organisms e.g. wash hands). Might be - pathogenic/non-pathogenic. Might be on skin or other body surfaces. Doesn't lead to injury/invasion of tissues
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What is colonisation?
Continuing presence of microbes (weeks/months/years). No injury/invasion of tissues. Useful purpose usually
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What is the difference between contamination and colonisation?
Time course
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How to microbes cause infection in simple terms?
Injury to or invasion and damage of tissues
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Microbes can be categorised into which three groups?
Normal flora (only inhabit surfaces of body - can be external or internal). Aggressive (primary) pathogens (microbes which cause disease in normal host). Opportunistic pathogens (microbes causing disease in hosts with impaired defences)
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Give an example of normal flora becoming aggressive pathogens
E.coli in gut (normal flora) moves to urinary tract (becomes aggressive pathogens) - causes UTI
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Describe features of normal flora
Microbes that co-exist with humans. live on body surfaces, includes mucous membranes (respiratory, genital, digestive, urinary systems)
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Which three aspects provide protection against invading microbes?
By weight of numbers, by production of proteins or antibiotics, by immune stimulation
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Give examples of normal flora found in different areas of the body (1)
Skin (S.epidermidis), eye (S.epidermidis), nose (S.epidermidis), mouth (Streptococci, Bacteriodes spp). Small bowel (Enterococci, E.coli, Klebsiella spp, Clostridium spp.). Colon (E.coli, Bacteroides spp, Clostridium spp)
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Give examples of normal flora found in different areas of the body (2)
Vagina (Clostridium spp, C. albicans)
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How is the response to infection monitored?
Basic parameters (fever, shock, inflammatory markers e.g. WBC, CRP etc). Specific physical signs (e.g. SOB, pneumonia)
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Describe features of fever (1)
Action of microbial cell wall components, cytokines and PGs on hypothalamus. Temperature of 37.4 degrees Celsius or higher - fever. Useful altering mechanism
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Describe features of fever (2)
Initially body attempts to conserve heat, vasoconstriction/headache/shivering/rigor - uncontrolled shivering. Continuing fever, body tries to lose heat, vasodilation/sweating (not harmful unless fluid loss/metabolic changes are excessive)
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Describe features of fever (3)
T above 40 can permanently affect organ function. T above 43 can kill. Don't always want to dampen fever (indicator of antibiotic effectiveness), try to avoid paracetamol use to bring temperature down (only use if patient cannot tolerate fever/pain)
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Describe features of shock (1)
Condition characterised by hypotension and decreased tissue perfusion (may be fatal consequence of sepsis). Commonest in bacterial infection (studied in Gram -ve infections). Uncommon in fungal infection
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Describe features of shock (2)
Due to complex cascade of inflammation, coagulation, fibrinolysis, hypotension. Hypotension and tachycardia (reduced BP, body tries to increase BP by increasing HR)
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Describe features of WCC (1)
Production stimulated from bone marrow as non-specific defence. Neutrophils (phagocytose extracellular bacteria, usually raised but may be low in severe infection). Macrophages/monocytes (most active against intracellular bacteria, protozoa, viruses)
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Describe features of WCC (2)
Eosinophils (involved in parasitic infections)
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Describe features of CRP (1)
Acute phase protein (binds to bacteria, activates complement pathway, causes opsonisation and phagocytosis). Sensitive test for infection/inflammation - may be raised post-operatively, after trauma, in chronic inflammatory conditions or malignancy
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Describe features of CRP (2)
Usual range of 0-5. Levels >50 usually significant , >100 highly significant. Raised in bacterial infection. Can be low in viral infection
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How is infection diagnosed? (1)
Patient history (prior/current medical history). Symptoms (hot/cold/shivering, rigors, nausea/vomiting, lethargy, rash, photophobia, diarrhoea, headache, abdominal pain, infective source)
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How is infection diagnosed? (2)
Rigors/extreme shivering (e.g. when infected with malaria) - cannot be controlled easily. Chicken pox and measles have distinctive rashes. Patients with meningitis may have photophobia (sign of issue with CNS/brain function)
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How is infection diagnosed? (3)
Diagnosis (examination/questioning/severity of disease). History (of infection, PMH). Epidemiology/surveillance (travel/geography/occupation/hobbies/pets/sexual history)
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How is infection diagnosed? (4)
Physical examination (gives indication as to diagnosis and so possible causative organisms)
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How is infection diagnosed? (5)
Meningitis (headache, neck stiffness, photophobia). RTI (cough, purulent sputum, fever). UTI (dysuria, urgency, frequency, pain). Cellulitis (redness, swelling, pain)
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What are the investigations for infection? (1)
Biochemistry/haematology. FBC, clotting tests (PT, APTT, D-dimer, fibrinogen). Arterial blood gas, serum electrolytes, glucose, LFTs. ECG. Microbiology. Blood cultures, urine, swab infective sites/obtain pus sample, skin scrapings, sputum, faeces
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What are the investigations for infection? (2)
Bronchoalveolar lavage /bronchial brush. Tap effusion/ascites, lumbar puncture
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What are the other investigations as appropriate for infection?
X-ray (chest/abdomen). CT scan. MRI. Ultrasound. Echocardiogram. Surgical exploration
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Give examples of Gram positive bacteria (cocci)
Streptococci (pyogenes/viridans/pneumoniae). Staphyloccoci (aureus, epidermidis). Enterococci (faecalis/faecium)
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Give examples of Gram negative bacteria (cocci)
Neisseria (gonorrhoea, meningitides). Moraxella catarrhalis
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Give examples of Gram positive bacteria (rods)
Clostridia (difficile/perfringens, botulinum, tetani). Listeria (monocytogenes)
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Give examples of Gram negative bacteria (rods) -1
Salmonella (typhi/paratyphi). Pseudomonas (aeruginosa). E.coli. Klebsiella pneumoniae. Proteus vulgaris. Shigella sonnei. Helicobacter/Campylobacter/Enterobacter/Citrobacter/Acinetobacter
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Give examples of Gram negative bacteria (rods) -2
Haemophilus influenzae. Legionella pneumophila. Bacteroides fragilis
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Describe features of Streptococcus (1)
Facultative anaerobes, chains/pairs of cocci. S.pneumoniae cause range of infections from conjunctivitis to acute pneumonia and bacteria meningitis. S.pyogens cause pharyngitis, scarlet fever, wound sepsis, produce toxins, haemolysins/tissue necrosis
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Describe features of Streptococcus (2)
S.aures - nasal commensal, opportunistic pathogens produce toxins, pyogenic wound infection, bacteraemia, food poisoning, toxic shock syndrome, osteomyelitis, and pneumonia, MRSA. S.epidermis - skin commensal (wound infection)
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Describe features of Viridans Streptococci
Facultative anaerobes, cell chains. Common URT commensal streptococci. Opportunistic pathogens of immunocompromised. S. mutans causes dental caries. Cause endocarditis (in bloodstream, adhere to heart valves
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Describe features of Enterococci
Facultative anaerobes, diplococci. E. faecalis and E. faecium - common gut commensals. Opportunistic pathogens in immunocompromised. Produce cytolytic toxins. Vancomycin-resistant Enterococci - cause of nosocomial infections
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Describe features of bacilli (1)
Endospore forming rod-shaped aerobes and facultative anaerobes. B.anthracis - soil organism, causes opportunistic infection of wounds or lungs by spores, necrotic cytotoxins cause pathology (fatal if inhaled).
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Describe features of bacilli (2)
B.cereus (common soil/water organism, may contaminate food). Number of species produce antibiotics (e.g. polymyxin and bacitracin). Listeria - non-endospore forming rod shaped facultative anaerobes
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Describe features of bacilli (3)
L monocytogenes may contaminate meat/milk/grow in fridge, may invade phagocytes, cause fatal meningitis in immunocompromised patients or spontaneous abortion in pregnant women
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Describe features of Clostridia (1)
Endospore-forming rod- shaped obligate anaerobes. C. perfringens – intestinal organism, causes opportunistic infection of deep wound, produce cytotoxins (gas gangrene)
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Describe features of Clostridia (2)
C. botulinum - soil/water organism, may contaminate food, produces phage-coded neurotoxins which block ACh release at NMJ (botulism). C. tetani - soil organism, causes infection in deep wounds, produce toxins which block inhibitory motor neurone
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Describe features of Clostridia (3)
C. difficile - intestinal organism, may become predominant after broad-spectrum antibiotic therapy. Toxins induce haemorrhagic necrosis in intestine → explosive diarrhoea → pseudomembranous colitis (perforation of colon & massive infection)
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Describe features of actinobacteria (1)
Corynebacterium: non-endospore forming rod-shaped facultative anaerobes. C. diphtheriae - produces toxin coded by lysogenic β-phage. Toxin halts eukaryotic protein synthesis, causes cell necrosis, may cause death if released systemically (diphtheria)
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Describe features of actinobacteria (2)
Mycobacterium: Obligate aerobes, “acid fast” rods. M. tuberculosis – invade macrophages & form invasive necrotic tubercles.
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Describe features of actinobacteria (3)
Actinomycetes: Filamentous polynucleate tubes called hyphae. Actinomyces sp. – normal flora of mucosa, may cause aggressive opportunistic infection.
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Describe features of actinobacteria (4)
Streptomyces sp. – non-pathogenic, produce many antibiotics (tetracycline, chloramphenicol, erythromycin, nystatin, neomycin etc.)
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Describe features of Gram negative cocci/rods (1)
β-proteobacteria: includes Neisseria. N. gonorrhoeae – cause of STI gonorrhoea, cells cause invasive infection of connective tissue → scarring → sterility. May affect other area through contact inc. eyes of newborns.
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Describe features of Gram negative cocci/rods (2)
N. meningitides – may be carried asymptomatically, causes childhood meningitis. γ-proteobacteria: includes Legionella & Pseudomonas.
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Describe features of Gram negative cocci/rods (3)
L. pneumophila - aerobic IC parasites of protozoa in water. Infect humans via droplets from showers, aircon etc. Cause pneumonia. P. aeruginosa – in soil & water. Opportunistic pathogen in humans, toxins/virulence factors (cell necrosis)
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Describe features of Gram negative cocci/rods (4)
Forms biofilms in polysaccharide matrix persistent infection in CF lung.
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Describe features of Gram negative rods (1)
Enterobacteriaceae. Escherichia coli – normal flora but can cause gastroenteritis urinary tract infections (inc. bladder & kidney) and bacteraemia. Salmonella sp. – all species are pathogenic → enteritis. Shigella sp. – dysentery.
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Describe features of Gram negative rods (2)
Yersinia pestis – infects lymphatic system bubonic & pneumonic plague. Klebsiella pneumoniae – pneumonia, bacteraemia & UTIs. Proteus sp. – bacteraemia & UTIs. Citrobacter sp. Enterobacter sp. - Nosocomial infections. Serratia sp.
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Describe features of Gram negative rods (3)
Horizontal gene transfer is very common amongst these organisms
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Describe features of Gram negative rods (4)
Vibrionaceae: Vibrio cholerae – cholera (CTXφ phage-coded toxin). Parvobacteria: Haemophilus influenzae – childhood meningitis, chronic bronchitis. Bacteroides sp. – commensals in mouth, colon (digest complex polysaccharides) & female genital tract
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Describe features of Gram negative rods (5)
Potentiate infections caused by enteric bacteria e.g. E. coli. Acinetobacter, aerobic coccobacilli. Acinetobacter baumannii – common cause of pneumonia in ICU (ventilator-associated) and catheter-related bacteraemia.
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Describe features of other Gram negative bacteria (1)
ε-proteobacteria. Helicobacter pylori – invasive colonisation of gastric mucosa (or important commensal). Campylobacter jejuni – contaminant of food, milk and water, causes gastroenteritis.
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Describe features of other Gram negative bacteria (2)
Spirochetes. Treponema pallidium – causes the STI syphilis. Chronic, develops over 30 years to invade all body tissue, results in skin lesions, blindness, paralysis, dementia, HF. Congenital syphilis in children (placental tranmission)
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Describe features of other Gram negative bacteria (3)
Borrelia burgdorferi – Transmitted by tick bite. Cause chronic infection resulting in encephalitis, neuropathy and arthritis.
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Describe features of pleomorphic bacteria (1)
Mycoplasma - lack to true cell wall, rigid form, membranes cholesterol. 0.15-0.3 microns. E.g. Mycoplasma pneumoniae, pneumonia (second most common cause) & urethritis
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Describe features of pleomorphic bacteria (2)
Chlamydia - Lack peptidoglycan obligate intracellular parasites with different forms in life cycle. 0.2-0.7 microns. Chlamydia spp. A major cause of oculo-genital disease.
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Describe features of identification - direct methods (1)
Microscopy, morphology, size/shape, grouping, Gram staining. Cultured from biological samples e.g. blood, sputum, urine, stool, biopsy, swabs, colony morphology, colour, changes to specialist media (haemolysis in blood agar)
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Describe features of identification - direct methods (2)
Biochemical tests, testing for metabolic products or possession of specific enzymes (e.g. catalase)
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Describe features of a complex culture media
May contain; yeast extract or blood or meat or serum or peptone or milk etc. Are not chemically defined and nutrient quantities will differ from batch to batch.
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Describe features of a defined culture media
Contents are fully chemically characterised, the quantities of each component being known. May contain many components, for culture of bacteria which require a number of growth factors.
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Describe features of a general purpose culture media
Nutrient broth or agar. Routinely used for culture of a wide range of bacteria, contains meat extract, peptone, NaCl
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Describe features of an enriched culture media
Contain ingredients which promote growth or specific bacteria. Blood agar is used to identify Streptococci. Pathogenic S. pyogenes secrete haemolysins which lyse blood cells in the agar, producing a clear zone around the colonies (β- haemolysis).
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Describe features of an selective culture media
Contain components which allow growth of some bacteria, but inhibit others
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What does MacConkey's agar contain?
Bile salts which inhibit growth of Gram +ves and promote growth of Gram –ve enteric bacteria. Lactose fermenting E.coli turn indicator pink.
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What does cetrimide agar contain?
Cationic detergent (QAC) cetrimide which selects for Pseudomonas aeruginosa and promotes the production of the blue-green pigment pyocyanin.
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What are indicator media?
Contain indicators to allow identification by biochemical characteristics. Mannitol salt agar, promotes the growth of Staphylococci as it contains 7.5% NaCl. Mannitol fermentation (S. aureus) is shown by change in colour of phenol red to yellow
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Describe features of identification - indirect methods (1)
Antibody techniques - Infected biological fluids mixed with monoclonal antibodies bound to latex particles. Aggregation of latex particles indicates presence of a specific antigen or organism
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Describe features of identification - indirect methods (2)
E.g. Staphylase test for the presence of surface coagulase on S. aureus.
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Describe features of identification - indirect methods (3)
Analytical profile index - Identification is based on the result of biochemical tests for specific enzymes of metabolic pathways. Test results are scored to produce an index number used to identify the organism.
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Describe features of identification - indirect methods (4)
MALDI-TOF - ID organisms using MS fingerprinting
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Interaction between organism and host. Usually peaceful and microbe may co-exist as normal flora. Can cause problems if state of host changes. Microbe may exist in environment - cause infection if it gets past host defences

Card 3

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What is infection? (3)

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Card 4

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What is infection? (4)

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Card 5

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