1. Microbiology

2. Microbiology
Phase 2a Revision Session Adam Temple and Dami Arewa 10/3/2017
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3. What we’ll cover The basics: staining + differentiating bacteria
Infections of each system
Tips + quiz
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4. Bacilli (rods)
Cocci
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5. Identification of Bacteria : 1. Gram Staining
Gram Positive
Purple
Gram Staining
Gram negative
Pink
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6. Gram Positive Bacteria
Streptococci
+ve
Gram Positive
Catalase Test
-ve
Important Gram Positive bacteria: Staphylococcus and Streptococcus
Staphylocooci
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7. Alpha haemolytic strep
Gram Positive chains of Cocci
Beta Haemolytic strep
Lancfield Group
Haemolysis test
Streptococci
Alpha haemolytic strep
Common beta haemolytic strep- Group B streptococcus- cause of meningitis in infants
Remember alpha is green- an apple is green
Optochin test
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8. S.aureus Gram Positive Clusters Coagulase test Staphylococcus +ve
S.aureus- golden colonies
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9. Gram staining Gram +ve or gram –ve? Gram +ve  Purple Gram –ve  Pink
Why does gram +ve stain purple and not pink?
Contains a thick layer of peptidoglycan in cell wall
Name the two big groups of gram +ve bacteria. What test can you do to distinguish them?
Staphylococci and streptococci
Catalase test (staph = catalase +ve) – you can also look under the microscope to see which are in chains (strep) or clusters (staph)
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10. Streptococci Gram +ve and catalse –ve Chains (strep = strip)
How do you distinguish them?
Haemolysis test: grow them on blood agar
Haemolysis:
Alpha haemolytic (partial/green)
Beta haemolytic (full/clear)
Gamma haemolytic (non)
Does anyone know any important alpha or beta haemolytic streptococci?
Alpha haemolytic: strep pneumoniae. How do you distinguish strep pneumoniae from other alpha haemolytic strep? The optochin susceptibility test. What happens if it is resistant? Then it is viridans strep
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11. Streptococci
Lancefield grouping? What organism is in group A that is resistant to optochin?
Beta haemolytic streptococci differentiation
Group A: strep. pyogenes
Does anyone know any important alpha or beta haemolytic streptococci?
Alpha haemolytic: strep pneumoniae. How do you distinguish strep pneumoniae from other alpha haemolytic strep? The optochin susceptibility test. What happens if it is resistant? Then it is viridans strep
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12. Staphylococci Gram +ve and catalase +ve Clusters
How do you distinguish them?
Coagulase test
Results:
Coagulase +ve = staphylococcus aureus (GOLD on blood agar)
Coagulase –ve = staph. Epidermidis
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13. Gram –ve Bacilli Can you give any examples?
E. coli
Pseudomonas spp.
Shigella
Salmonella
Campylobacter
What steps do you take to distinguish gram –ve bacilli?
1. MacConkey agar/XLD/CLED: Lactose and non-lactose fermenters
What are the big lactose fermenters? Klebsiella and E. coli
Non-lactose fermenters: shigella, salmonella, pseudomonas
2. distinguishing non-lactose fermenters: OXIDASE TEST  Psuedomonas oxidase +ve
Another big group you need to know about
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14. Non- Lactose fermenter Oxidase Test
e.g. E.coli
MacConkey/CLED/XLD
+ve
Pseudomonas sp
Non- Lactose fermenter
Oxidase Test
-ve
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15. Exam style Q
Under the microscope after gram staining it is reported that the organism from the sample you sent in is a gram negative cocci. What organism are you worried about?
Neisseria Meningitidis
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16. A 57 year old women is referred to hospital with a 6 week history of night sweats and malaise. She is noted to have a new cardiac murmur and some marks on her nails. She has a frequent history of dental problems and last visited the dentist 2 months ago.
What is going on here?
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17. Infective endocarditis
What?
Infection of endocardial lines structures (most commonly heart valves)
What’s the most common causative organism?
Streptococcus viridans
Other causes?
Streptococcus bovis, staphylococcus aureus, coxiella burnetti, H. influenzae…
Clinical features? (know at least 5 for exam)
New murmur
Fever
Osler’s nodes, Roth spots, splinter haemorrhages, Janeway lesions (which one isn’t in the hands?)
Septic Emboli (stroke, PE)
New onset murmur + fever  think IE until proven otherwise
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