Lab 12

• Gram-positive pathogenic cocci


  Genera such as Staphylococcus and Streptococcus that cause abscesses, impetigo, furuncles, carbuncles, osteomyelitis, and fatal septicemia
• Pyogenic or pus-forming cocci


  Collective term for Staphylococcus and Streptococcus
• Staphylococcus species


  • Arrange in clusters
  • Originally isolated from wounds but found to be part of normal microbiota of skin, and nasal membranes
• Pathogenic invasive Staphylococci (e.g. Staphylococcus aureus)


  • Tend to be hemolytic, coagulase-positive, with pigmented colonies (yellow) and able to ferment mannitol
  • Pathogenicity is dependent on ability to make extracellular toxins, enzymes and also on the state of host's health
• Nonpathogenic, noninvasive staphylococci (S. epidermidis)


  • Coagulase-negative, form nonpigmented white colonies and are unable to ferment mannitol
  • Members of normal microbiota of human skin and respiratory and gastrointestinal tracts
• Streptococcus species


  • Arrange in chains, are catalase-negative, and exhibit various patterns of hemolysis on a blood agar plate
  • Many found in throat, mouth, nose and intestine
• Pathogenic Streptococcus species


  • Associated with diseases such as strep throat, scarlet fever, impetigo, bacterial pneumonia, puerperal fever, and necrotizing fasciitis
• Streptolysins


  Enzymes produced by some Streptococcus species that completely lyse the blood cells in a blood agar (beta hemolysis)
• Alpha hemolysis


  Partial lysis of blood cells producing a greenish hue on a blood agar plate
• Gamma hemolysis


  No lysis of blood cells, no hemolysis
• Streptococcus groups


  • A through R
  • Groups A through D, many show beta hemolysis
  • Group D enterococci also referred to as the fecal group of streptococci
• Neisseria


  Gram-negative diplococci that can be differentiated from other cocci by a positive oxidase reaction
• Major Neisseria pathogens


  • N. meningitidis and N. gonorrhoeae
• Mannitol Salt Agar (MSA)


  • Selective and differential medium that selects for halotolerant bacteria such as members of the genus Staphylococcus
  • Contains mannitol and phenol red, acidic byproducts from mannitol fermentation turn phenol red yellow
• Trypticase Soy Agar (TSA)


  Allows growth of most bacteria, serves as a control for MSA
• Oxidase test


  Detects the presence of cytochrome oxidase, a valuable tool in differentiating among bacteria
• Catalase test


  Detects the presence of catalase enzyme that splits hydrogen peroxide into water and oxygen, used to differentiate Staphylococcus from Streptococcus
• Salt broth test


  Tests for salt tolerance, used to differentiate Group D Streptococci
• Bile Esculin test


  Tests for esculin hydrolysis, used to differentiate Group D Streptococci
• Coagulase test


  Detects the presence of coagulase produced by pathogenic Staphylococcus aureus
• Novobiocin sensitivity test


  Differentiates between non-invasive Staphylococcus species, S. epidermidis is sensitive while S. saprophyticus is resistant
• Significant percent of all the bacterial infections are caused by cocci from few genera: Staphylococcus, Streptococcus, Neisseria
• Not all species are equally virulent, many are part of normal microbiota
• Streptococcus species are catalase-negative
• Staphylococcus species are facultative anaerobes, catalase-positive, halotolerant, and acid tolerant
• Staphylococcus aureus is coagulase-positive, hemolytic, and mannitol-fermenting, while non-pathogenic Staphylococcus species are coagulase-negative, non-hemolytic, and generally non-mannitol fermenters
• Neisseria species are Gram-negative diplococci, oxidase-positive, and catalase-positive