Summer

• Gram-positive cocci


  • Peptococcus
  • Peptostreptococcus
  • Sarcina
  • Micrococcus
  • Staphylococcus
  • Streptococcus
• Gram-negative cocci


  • Neisseria
  • Moraxella
  • Acinetobacter
  • Kingella
• Neisseria


  • Kidney, coffee bean shaped
  • Encapsulated
  • Obligate aerobes
  • Capnophilic (requires 3-10% CO2)
  • Catalase & oxidase (+)
  • Fastidious
  • Pathogenic species grow only @ 37°C
  • Non-motile
  • Non-sporeformer
  • Non-hemolytic
  • Non-pigmented
• Neisseria gonorrhoeae


  Gonococci, agent of gonorrhea
• Neisseria meningitidis


  Meningococcus, causative organism of Meningococcal (epidemic) Meningitis
• Moraxella catarrhalis


  Formerly Branhamella catarrhalis, Neisseria catarrhalis<|>Aerobic, oxidase-positive diplococcus<|>Morphologically and biochemically resembles Neisseria<|>Will not grow on modified Thayer Martin and does not ferment any sugar<|>Differentiated on DNA-based composition
• Identification of Gram-positive cocci

  1. Catalase test

  2. Coagulase test
• Catalase test


  Staphylococci and Micrococci are capable of producing the enzyme catalase, which can be tested by mixing the bacteria with hydrogen peroxide and observing for oxygen bubbling
• Coagulase test


  Used to differentiate Staphylococcus aureus (positive) from Coagulase Negative Staphylococcus (CoNS)<|>Coagulase is an enzyme produced by S. aureus that converts soluble fibrinogen in plasma to insoluble fibrin
• Slide test


  This strain must be tested in the tube test
• Quality Control


  To keep expenses at a minimum, it is possible to do one positive and one negative control for the class as a whole, instead of having each student or group perform them
• Clumping in the slide test

  Might not be easily observed by holding the slide on top of the workbench. It will be more visible when observed over a dark surface
• If the student has allowed enough time for the drop of plasma to dry on the slide

  Then there may be a false-positive response. Encourage the students to be aware of this possibility before they start
• If the strain shows clumping only when emulsified in the plasma and there is no autoagglutination

  This is a positive slide test. This strain is not further tested in the tube test
• If the strain shows no clumping in either saline or plasma

  It has tested negative on the slide coagulase test and should be further tested using the tube coagulase test
• Positive control species


  Should show clumping only when emulsified in the plasma
• Negative control species


  Should not show clumping in either water (saline) or plasma
• A negative slide coagulase test


  Is not valid and should be followed with a tube test for confirmation
• Rabbit plasma


  May be obtained by centrifuging blood to which 0.1% EDTA has been added as anticoagulant. Alternatively, it may be obtained lypophilized from a commercial supplier and reconstituted by the addition of water
• Citrated human plasma


  May be obtained from a blood bank, but the blood must have been screened and found free from viral (Hepatitis B, HIV) antigens and antibodies. It must be handled with the precautions appropriate for all human body fluids
• Storing plasma


  Store the plasma in small portions at -20°C and keep a stock of in-used plasma at 4°C bringing it to room temperature before use
• Positive and negative control organisms

  • Positive control organism: Staphylococcus aureus
  • Negative control organism: Staphylococcus epidermidis
• Coagulase Test
• GM (+) COCCI
• Staphylococcus spp.
• S. aureus
• S. epidermidis
• S. saprophyticus
• Streptococcus spp.
• S. pneumoniae
• Viridans gp
• S. Pyogenes (GAS)
• S. Agalactiae (GBS)
• 6.5% NaCl
• E. faecalis
• E. faecium
• S. bovis
• Isolation of Gram-positive Cocci
• Novobiocin


  An antibiotic interfering with the unpacking and repacking of DNA during DNA replication and the bacterial cell cycle. It binds to DNA gyrase, and blocks adenosine triphosphatase (ATPase) activity
• Novobiocin test


  Differentiates CoNS