Micro Lab practical 3

• Beta hemolysis

  Complete hemolysis, colorless with yellow hue around it
• Alpha hemolysis

  Partial hemolysis, greenish/yellowish color
• Gamma hemolysis

  No hemolysis/no change
• MSA

  • Yellow for mannitol fermenter
  • Positive for mannitol fermenter
  • Negative for non-fermenter
• Blood agar


  Media used to illustrate hemolysis
• Mannitol Salt Agar (MSA)

  • Selective media due to 7.5% NaCl
  • Differential media due to fermentation of mannitol
• Coagulase positive test


  • Advantage for the bacteria as it helps them evade, cause disease, and colonize
  • Positive test results in clumping of the bacteria
• Antigen-antibody testing


  immunologic method of identifying microorganisms
• Which disinfectant is effective for all bacteria? Hydrogen peroxide

  b.Which disinfectant works best for E.coli? bathroom cleaner

  c. Do you need a reference table when working with disinfectants to determine effectiveness? No, >more than 2mm is sensitive/effective <less than 2mm is resistant/ineffective

  
• Which side of the plate is showing sensitivity to novobiocin? right side

  b.Which microorganism did we learn in lab would be resistant to novobiocin? S. saprophyticus

  c.Which microorganism would be sensitive to novobiocin? Streptococcus epidermis

  
• What ingredient makes Columbia CNA media selective? colistin and nalidixic acid

  b. What ingredient makes Columbia CNA media differential? sheeps blood

  c. Which bacteria are likely in quadrants 2 and 3? Entrtobacter aerogenus, Escherichia coli, gram-negative bacteria

  d. Why are bacteria growing in quadrants 1 and 4? Enterococcus faecalis and Staphylococcus aureus, gram positive

  
• Based on the hemolytic activity and optochin disk, identify the

  genus and species most likely isolated on this plate.  Streptococcus pneumonia

  
• Based on the observations with hemolytic activity and bacitracin,

  identify the genus and species most likely isolated on this plate. S.pyogenes

  
• Identify the type of hemolysis (complete) shown at the arrow. Beta

  b. What type of media (agar) is used to illustrate hemolysis? 5% sheeps blood

  
• Identify this selective and differential media that allows for Differentiation between Staph. aureus and Staph. epidermidis. Selective- 7.5 NaCl differential- Fermentation of mannitol

  b. Name which sector you would find S. aureus. sector 1

  c.Name the ingredient that makes this plate “selective”. 7.5 NaCl

  d.Why is sector “1” turning yellow? fermentation of mannitol

  
• Identify this bacteria as being susceptible or resistant to the

  Optochin on the agar surface.  resistant

  
• An enteric culture gave the following results: gram positive cocci,

  Gamma/alpha hemolytic, bacitracin negative, optochin negative,

  Bile esculin slant tube entirely black, 6.5% NaCl broth turbid. a.Based on the results above, name the genus and species of the most likely bacteria. Enterococcus faecalis aks streptococcus faecalis

  b. Name the beta-hemolytic, gram-positive bacteria that is found in the Group B streptococcus organisms.  Streptococcus agalactiae
• A throat culture gave the following results: gram positive cocci in

  chains, beta hemolytic, catalase negative, and bacitracin susceptible.

  a.Name the most likely genus and species based on the results

  Above. Streptococcus pyogenes

  b.Name which group this bacteria would be found. Group a streptococcus
• What bacteria did we learn about that would have a coagulase positive test? Staphylococcus aureus

  
• Why is there clumping in seen in the SA sample but not in the SE sample?  antigens