Diag Micro Strep MH 2024 MLS Diploma L2 (1) - Tagged:

Introduction to Diagnostic Microbiology

• / Author: Maria Dannessa Delost

• Focus on laboratory sciences related to microbiology.

Chapter 2: Streptococcus, Enterococcus and Related Organisms

Streptococcus

• Normal Flora: Present on skin, nose, mouth, mucous membranes, and gastrointestinal tract of humans and animals.

• Environmental Presence: Found in dairy products.

• Characteristics:

  • Catalase negative.

  • Gram-positive cocci, appearing in pairs or chains.

• Isolation: On blood agar or selective blood agar media.

Hemolysis Types

• Complete Hemolysis: Beta Hemolysis

• Partial Hemolysis: Alpha Hemolysis

• No Hemolysis: Gamma Hemolysis

Lancefield's Classification

• Streptococci classified based on specific cell wall carbohydrate antigens.

Latex Agglutination Test

• Used for identifying streptococci.

Streptococcus pyogenes (Group A Streptococcus)

• Primary Infections:

  • Bacterial pharyngitis.

  • Skin infections.

  • Invasive diseases.

• Identification:

  • Colonial morphology: pinpoint, translucent, or clear, with wide zone of beta hemolysis.

  • Bacitracin test: Susceptible to 0.02-0.04 units of bacitracin.

GAS Infections

• Includes bacterial pharyngitis, tonsillitis, scarlet fever, and skin infections like impetigo.

Invasive GAS Infections

• Conditions: Streptococcal toxic-shock-like syndrome (TSLS) and necrotizing fasciitis.

Streptococcus agalactiae (Group B Streptococcus)

• Cultural Characteristics:

  • Medium size, flat, opaque colonies on sheep blood agar.

  • Narrow zone of beta hemolytic or nonhemolytic.

• Importance: Can cause infections in newborns during birth.

Identification of Group B Streptococcus

• CAMP Factor: Shows synergistic hemolysis.

• Hippurate Hydrolysis: Positive test.

Streptococcus pneumoniae

• Appearance: Gram-positive cocci in pairs.

• Isolation: Requires 5-10% CO2 on sheep blood agar.

Identification Tests for S. pneumoniae

• Bile Solubility Test:

  • Positive appears as clearing in the presence of bile.

• Optochin Test:

  • Identification by measuring zone of inhibition after applying optochin disc.

Infections Caused by S. pneumoniae

• Common cause of community-acquired pneumonia, sinusitis, otitis media, and meningitis.

Enterococcus

• Natural Habitat: Found in environment; normal flora of the gastrointestinal and genitourinary tract.

• Species:

  • E. faecalis (80-90% infections)

  • E. faecium (5-10% infections)

Enterococcus Infections

• Associated with opportunistic infections, such as urinary tract infections and endocarditis.

Identification of Enterococcus

• Cultural Characteristics: Grayish colonies, a hemolytic or nonhemolytic.

• Growth in 6.5% NaCl broth and PYRase positive.

Bile Esculin Test

• Used for presumptive identification of Group D antigen.

• Assesses growth in 4% bile and esculin hydrolysis.