Microbiology
Microbiology Phase 2a Revision Session Adam Temple and Dami Arewa 10/3/2017 The Peer Teaching Society is not liable for false or misleading information…
What we’ll cover The basics: staining + differentiating bacteria Infections of each system Tips + quiz The Peer Teaching Society is not liable for false or misleading information…
Bacilli (rods) Cocci The Peer Teaching Society is not liable for false or misleading information…
Identification of Bacteria : 1. Gram Staining Gram Positive Purple Gram Staining Gram negative Pink The Peer Teaching Society is not liable for false or misleading information…
Gram Positive Bacteria Streptococci +ve Gram Positive Catalase Test -ve Important Gram Positive bacteria: Staphylococcus and Streptococcus Staphylocooci The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
S.aureus Gram Positive Clusters Coagulase test Staphylococcus +ve S.aureus- golden colonies The Peer Teaching Society is not liable for false or misleading information…
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) The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
Non- Lactose fermenter Oxidase Test e.g. E.coli MacConkey/CLED/XLD +ve Pseudomonas sp Non- Lactose fermenter Oxidase Test -ve The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…
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? The Peer Teaching Society is not liable for false or misleading information…
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 The Peer Teaching Society is not liable for false or misleading information…