Streptococcus Quiz - NEET Pattern

Streptococcus Overview

• Catalase negative beta hemolytic streptococci include Streptococcus pyogenes, while S. pneumoniae and S. viridans are alpha hemolytic, and Enterococcus is non-hemolytic.
• Lancefield grouping classifies beta hemolytic streptococci based on C carbohydrate antigen.

Clinical Characteristics

• A case involving a skin ulcer in a boy and sore throat in children revealed beta hemolytic streptococci; C carbohydrate antigen can determine if they are the same strain.
• Streptococcus pyogenes is noted for causing necrotizing fasciitis and is sensitive to bacitracin, whereas S. agalactiae is resistant.

Classification and Tests

• Lancefield classification uses C carbohydrate antigen for categorization from A to V; M protein is further used in Group A classification (Griffith typing).
• Isolation of Streptococcus pyogenes for sore throat requires blood agar; it's commonly implicated in throat infections.
• A CAMP test is positive for Group B streptococci, differentiating them from Group A.

Pathogenesis

• Streptococcus pyogenes can cause severe conditions like neonatal meningitis and endocarditis; Group B is particularly responsible for neonatal infections.
• Streptococcal Toxic Shock Syndrome is attributed to pyrogenic exotoxin.
• Enterococcus, specifically E. faecalis and E. faecium, displays resistance to many antibiotics, necessitating combined therapy with aminoglycosides.

Diagnosis

• A child with culture positive for gram positive cocci in chains suggests a β hemolytic streptococcus; sensitivity to bacitracin can help distinguish between Group A (sensitive) and Group B (resistant).
• An outbreak of Streptococcal Pharyngitis in a village requires culture transport media, with Pike's media being ideal.

Common Pathogens

• Streptococcus pyogenes is the most common cause of cellulitis; Staphylococcus aureus is also a frequent pathogen.
• Gram positive cocci isolated during infections may show characteristics like bacitracin sensitivity, distinguishing pathogens like S. pyogenes.
• S. pneumoniae is a leading cause of pneumonia and is identifiable by its bile solubility.

Treatment Protocols

• Treatment for necrotizing fasciitis includes surgical debridement and antibiotics like Penicillin and Clindamycin.
• Vancomycin resistant Enterococci (VRE) cases complicate treatment; combination therapy with penicillin and aminoglycosides is essential.

Important Tests and Sensitivities

• Use Optochin sensitivity test to differentiate between S. pneumoniae and S. viridans.
• C-reactive protein (CRP) is produced in response to inflammation and reacts with C carbohydrate antigen of pneumonia-causing bacteria.
• Sensitivity tests such as those for bacitracin and bile solubility help confirm diagnoses.

Summary of Key Points

• M protein enhances virulence by inhibiting phagocytosis; capsules can also contribute to virulence.
• Streptococcal infections can lead to varied clinical manifestations, and precise identification is crucial for effective treatment and management.
• Continuous monitoring for antibiotic resistance patterns in streptococci is necessary for ensuring appropriate therapeutic strategies.### Optochin Sensitivity
• Optochin sensitivity is used to differentiate Streptococcus pneumoniae from Streptococcus viridans.
• Pneumococcus is sensitive to a 5µg optochin disc, whereas Strept viridans is resistant.
• Isolation of alpha-hemolytic colonies suggests pneumococcal pneumonia, particularly in patients presenting with fever and respiratory distress.

Sputum Culture Results (70-Year-Old Male)

• The cultured sputum from a 70-year-old male on 5% sheep blood agar produced alpha-hemolytic colonies.
• Expected identification:
  • Gram positive cocci in pairs
  • Catalase negative
  • Bile soluble
• Indicative of Streptococcus pneumoniae.

Infection Risks Post-Splenectomy

• In splenectomized patients, risk of infection increases for capsulated organisms.
• All listed organisms except Staphylococcus aureus are capsulated:
  • Pneumococcus
  • Klebsiella
  • Haemophilus influenzae
• The spleen helps remove capsulated organisms through opsonization.

Pneumococcal Vaccine Information

• The pneumococcal vaccine is made from capsular polysaccharides.
• It is not routinely administered but is provided to high-risk groups.
• Pneumococcus exhibits:
  • Catalase negative
  • Oxidase negative
  • Bile soluble
  • Optochin sensitive

Lobar Pneumonia Causative Organisms

• Streptococcus pneumoniae is the most common cause of lobar pneumonia.
• In adults, the most common serotypes associated are types 1-8.
• In children, common serotypes include 6, 14, 19, and 23.
• Serotype 3 is noted as the most virulent.

Capsular Resistance to Phagocytosis

• Polysaccharide capsules provide resistance to phagocytosis against several organisms, including:
  • Neisseria meningitidis
  • Klebsiella pneumoniae
  • Streptococcus pneumoniae

Orbital Cellulitis Culture Results

• In cases of orbital cellulitis, greenish colonies and optochin sensitivity on culture suggest Streptococcus pneumoniae.

Acute Otitis Media Causative Organisms

• The most common organism causing acute otitis media is Streptococcus pneumoniae.
• Other notable organisms include Haemophilus influenzae and Moraxella catarrhalis, frequently isolated from middle ear fluid in children.