Staphylococcus_Streptococcus_Neisseria

• What are the two main genera of Gram-positive cocci?

  Staphylococci and Streptococci

  
• What are the general properties of Staphylococcus?

  • Widely distributed in nature
  • Part of normal human and animal flora
  • Gram-positive cocci clustered in groups
  • Facultative anaerobes
  • Not fastidious, grow easily
  • Grow in presence of 7.5% sodium chloride
• How many medically important species are in the Staphylococcus group?

  Three medically important species
• What is the most common species of Staphylococcus responsible for infections in humans?

  Staphylococcus aureus
• What type of infections does S. epidermidis typically cause?

  Opportunistic infections in immunocompromised patients
• What type of infections can S. saprophyticus cause?

  May cause urinary tract infections
• What are the structural components of Staphylococcus aureus?

  • Species-specific teichoic acid
  • Species-specific protein A
  • Unique peptidoglycan
• What is the role of the capsule in Staphylococcus virulence?

  Inhibits chemotaxis and phagocytosis
• What does peptidoglycan provide for Staphylococcus?

  Osmotic stability and stimulates pyrogen production
• What is the function of Protein A in Staphylococcus?

  Inhibits antibody-mediated clearance
• What are the types of toxins produced by Staphylococcus aureus?

  • Cytotoxins (α, β, δ, γ, leukocidin)
  • Exfoliative toxins (ETA, ETB)
  • Enterotoxins (A-E, G-I)
  • Toxic shock syndrome toxin-1
• What is the effect of enterotoxins produced by S. aureus?

  Stimulate T cell proliferation and cytokine release
• What is the role of coagulase in Staphylococcus aureus?

  Converts fibrinogen to fibrin, clumping staphylococci
• What are the common epidemiological features of S. aureus?

  • Normal flora on human skin
  • Colonizes skin and mucous membranes of 30% of humans
  • Survives on dry surfaces for long periods
  • Spread through direct contact or contaminated fomites
• What are the risk factors for S. aureus infections?

  Presence of foreign body and previous surgery
• What diseases are caused by Staphylococcus aureus?

  • Scalded skin syndrome
  • Food poisoning
  • Toxic shock syndrome
  • Superficial infections
  • Deep infections (bacteremia, pneumonia, osteomyelitis)
• What characterizes scalded skin syndrome?

  Disseminated desquamation of epithelium
• What is the typical onset of food poisoning caused by S. aureus?

  Rapid onset of vomiting and diarrhea
• What is the primary cause of toxic shock syndrome?

  Strains producing TSST-1
• What are the characteristics of superficial infections caused by S. aureus?

  • Intense suppuration
  • Local tissue necrosis
  • Formation of pus-filled abscess
• What is the primary cause of bacteremia and endocarditis?

  Spread of bacteria into the blood
• What is the typical presentation of pneumonia caused by S. aureus?

  Consolidation and abscess formation in lungs
• What is osteomyelitis?

  Destruction of bones, particularly in children
• What are the laboratory diagnosis methods for S. aureus infections?

  1. Microscopic examination
  2. Culture and isolation
  3. Biochemical identification
• What does the coagulase test indicate?

  Presence of S. aureus in culture
• What are the treatment options for S. aureus infections?

  • Antibacterial treatment with oxacillin or vancomycin
  • Drainage of abscess
  • Symptomatic treatment for food poisoning
• What are the general properties of coagulase-negative staphylococci?

  • Catalase-positive
  • Coagulase-negative
  • Gram-positive cocci in clusters
  • Facultative anaerobes

  
• What diseases are associated with coagulase-negative staphylococci?

  • Catheter-related bacteremia
  • Subacute endocarditis
  • Surgical wound infections
• What are the general properties of Streptococcus?

  • Gram-positive cocci forming linear chains
  • Catalase negative
  • Mostly facultative anaerobes
  • Fastidious organisms, grow best in blood agar
• How are streptococci classified based on hemolysis pattern?

  1. Alpha-hemolytic (incomplete hemolysis)
  2. Beta-hemolytic (complete hemolysis)
• What is the appearance of alpha-hemolytic streptococci on blood agar?

  Green appearance on blood agar

  
• What is the appearance of beta-hemolytic streptococci on blood agar?

  Clear zone in the blood agar

  
• What are the notable exceptions in alpha-hemolytic streptococci?

  • Most lack a polysaccharide capsule
  • S. pneumoniae is a notable exception
• What are the characteristics of beta-hemolytic streptococci?

  • Exhibit complete hemolysis
  • Not all are pathogenic
• What is the classification basis for streptococci?

  Based on hemolysis pattern
• What do vascular catheters help prevent?

  Infections
• What genus includes a large number of species that are mostly normal flora?

  Genus Streptococcus
• What type of pathogens are some species of Streptococcus?

  Frank pathogens
• Where are most Streptococcus species found in the human body?

  Oropharynx and gastrointestinal tract
• What is the Gram stain result for Streptococcus species?

  Gram positive cocci