Microbiology Lecture Notes

Overview of Bacterial Classification

Gram Positive Cocci

• General Characteristics:
  • Gram Positive (G+), Catalase (-)
  • Cocci shape

Hemolytic Classification of Streptococci

• Beta hemolytic: Commonly associated with:
  • Strep pyogenes (Group A): Gram +, catalase -
  • Strep agalactiae (Group B):
  • + Bile esculin
  • + PYR/6.5% NaCl
  • Not Group A, B, or D
• Alpha hemolytic: Includes:
  • Strep pneumoniae
  • S or + PYR/Bacitracin R or --
  • S Optochin disc R
  • Streptococcus viridans:
  • + Hippurate/CAMP -

Enterococcus

• Considerations:
  • Positive for Bile esculin
  • Positive for PYR/6.5% NaCl
  • Group D designation

Gram Positive Cocci - Staphylococci

• Staphylococcus aureus:
  • + Coagulase
• Micrococcus:
  • General characteristics:
  • Gram Positive (G+), Catalase (+)
• Coagulase Negative Staphylococcus:
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

Gram Positive Bacilli

• General characteristics:
  • Gram Positive (G+), Bacilli shape
• Notable Organisms:
  • Bacillus spp.:
  • + Spore forming
  • Bacillus anthracis
  • Nocardia:
  • + Catalase-
  • Erysipelothrix
  • Lactobacillus
  • Gardnerella
  • Listeria:
  • + Motility/Bile esculin -
  • Corynebacterium:

Overview of Gram Negative Bacilli

Enterobacteriaceae Family

• General characteristics:
  • Gram Negative (G-) Bacilli
  • All have:
  • Oxidase: -
  • Catalase: +
  • Nitrate reduction to Nitrite
  • Ferment glucose
  • Facultative anaerobes

MacConkey Agar Results:

• Lactose Fermenters (Mac LF):
  • Escherichia coli
  • Klebsiella
• Non-Lactose Fermenters (Mac NLF):
  • Citrobacter
  • E. coli
  • Enterobacter

Specific Biochemical Tests within Enterobacteriaceae

• Methyl Red Test:

  • Positive:
  • E. coli
  • Negative:
  • Citrobacter

• Citrate Utilization Test:

  • Positive:
  • E. aerogenes
  • Klebsiella
  • Enterobacter cloacae
  • Negative:
  • Citrobacter
  • E. coli

Significant Genera and Species:

• Shigella (S)
• Serratia
• Salmonella (S)
• Edwardsiella (E)
• Yersinia (Y)
• Proteus (P)
• Morganella (M)
• Providencia (P)

Summary of Specific Biochemical Features of Enterobacteriaceae

• Salient Properties:
  • + Motility for:
  • Proteus
  • Morganella (but with + H2S in Edwardsiella and Salmonella)
  • Phenylalanine Deaminase Test:
  • Positive in:
    • Morganella
    • Providencia
  • Negative:
    • Other genera
• Methyl Red Test:
  • Positive in Yersinia and Serratia

Noteworthy Species under Genera:

• Shigella sonnei:
  • + Mannitol, - ONPG
• Shigella flexneri:
  • ODC positive
• Yersinia pestis and Yersinia enterocolitica:
  • + Motility at 25°C for Yersinia pseudotuberculosis