Bio 348: Staphylococcus

Introduction

  • The upcoming lectures differ from those covered in textbooks, focusing on content taught at other institutions.
  • The information being presented is simplified, recognizing that not all details are necessary for the audience's context.
  • Emphasis is placed on disease states relevant for non-nursing majors.

Aerobic Gram Positive Cocci

Overview

  • The discussion will concentrate on aerobic gram positive cocci, frequently isolated from patient samples.
    • Key organisms include:
      • Coagulase negative Staphylococci (CNS)
      • Staphylococcus epidermidis
      • Staphylococcus aureus
      • Micrococcus species
  • Many of these organisms are part of the body's normal flora, found on skin and mucous membranes but can be opportunistic pathogens.
  • The upcoming lectures will assist students with their unknown organisms related to their lab work.

Genera of Focus

Staphylococcus and Micrococcus

  • Both genera belong to the family Micrococcaceae.
  • Characteristics of these organisms:
    • They are gram positive cocci arranged in clusters (grape-like).
    • All are catalase positive, meaning they produce bubbles in the presence of hydrogen peroxide due to catalase enzyme activity.
    • Facultative anaerobes: can grow in both aerobic and anaerobic conditions.
    • Gram positive cocci can appear in pairs or tetrads (four cells together).

Laboratory Techniques

  • Gram Staining: Identifies gram positive cocci.
  • Catalase Test: Following gram staining, the catalase test is vital.
    • Positive test results (bubbles) indicate the presence of Staphylococci.
    • Negative test results suggest possible Streptococci or Enterococci.
  • Coagulase Test: Clarifies between Staphylococcus species, although not done in lab.
  • Mannitol Salt Agar (MSA): Used for differentiating Staphylococcus aureus from other staphylococci:
    • Contains high levels of salt to inhibit other bacteria.
    • Staphylococcus aureus ferments mannitol, turning the medium yellow.
    • Other staphylococci remain red on the MSA due to non-fermentation of mannitol.

Staphylococcus aureus

  • Commonly encountered in hospitals.
    • Colonization: Often found in the nostrils of patients; MRSA screening required upon admission.
    • Morphology: Exhibits golden yellow colonies due to the gold (Au) in its name.
  • Hemolysis Patterns on Blood Agar:
    • Alpha Hemolysis: Greenish discoloration due to partial lysis of red blood cells.
    • Beta Hemolysis: Clear zones indicating complete lysis.
    • Gamma Hemolysis: No lysis indicated.
    • Staphylococcus aureus is marked by beta hemolytic activity.
  • Biochemical Identification:
    • Catalase positive and coagulase positive.
    • Growth and yellow color change in MSA confirm identity.
  • Virulence Factors:
    • Coagulase: Converts fibrinogen to fibrin, aiding in clot formation and identifying pathogens.
    • Protein A: Binds antibodies in an inappropriate manner, evading immune response.
    • Hemolysins: Break down red blood cells, enhancing pathogenicity.
    • Production of various toxins including alpha and beta toxins associated with cell lysis and gastroenteritis.
  • Clinical Significance and Infections:
    • Causes food poisoning, toxic shock syndrome, scalded skin syndrome, skin infections, and bacteremia.
    • Shirley response includes:
      • Folliculitis: Inflammation of hair follicles.
      • Furuncles: Boils or pus-filled infections.
      • Carbuncles: Aggregated furuncles.
      • Impetigo: Honey-crusted lesions, particularly in children.
      • Serious conditions include osteomyelitis, pneumonia, and meningitis.

Coagulase Negative Staphylococci (CNS)

  • Various species, often considered non-pathogenic unless found in sterile sites.
  • Staphylococcus epidermidis:
    • Commonly identified in labs as the most prominent CNS.
    • Non-hemolytic and often part of skin flora; exhibits gamma hemolytic pattern on blood agar.
    • When isolated from prosthetic devices or sterile sites, higher concern for pathogenicity requires further treatment evaluation.
  • Staphylococcus saprophyticus:
    • Identified as a UTI pathogen, primarily affects women.
    • Urease positive, showing a pink coloration in the urease test.
    • These features make it clinically significant, particularly in diagnosing urinary tract infections.

Micrococcus

  • Typically as non-pathogenic skin flora and can be differentiated in lab contexts.
  • This organism is an obligate aerobe and non-hemolytic, appearing in clusters similar to staphylococci.
  • Micrococcus luteus and Micrococcus roseus demonstrate yellow and pink pigments, respectively (insoluble pigments).
  • Identification through differential tests concerning catalase and oxidase activity, often ignored unless linked to health significance in immunocompromised patients.

Conclusion

  • The study of aerobic gram positive cocci provides an essential foundation for understanding clinical microbiology and infectious diseases encountered in medical settings.