Questions and Answers
What does bile solubility help differentiate?
Pneumococcus from Streptococcus viridans
What does the 'C' in C reactive protein stand for?
In a case of respiratory distress with α-haemolytic colonies growth, which susceptibility agent is relevant?
What is the likely result of culturing a sputum specimen showing α-haemolytic colonies?
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In a splenectomized patient, which organism does not lead to increased infection risk?
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Which statement about Streptococcus pneumoniae is true?
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What is the most common causative organism for lobar pneumonia?
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Which organism is known for its polysaccharide capsule resistance to phagocytosis?
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In a patient with orbital cellulitis, if the culture shows greenish colonies and Optochin sensitivity, what is the most likely organism?
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What is the most common organism causing acute otitis media?
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Catalase negative beta hemolytic streptococci is:
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What is the characteristic which can tell if the strains are the same or different?
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Lancefield grouping of streptococci is done by using:
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True about streptococcus:
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Lancefield classification is based on:
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Which medium is used to culture the throat swab for a child with sore throat?
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False regarding Streptococcus pyogenes:
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Necrotizing fasciitis is caused by:
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All are true about Streptococcus pyogenes except:
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Which streptococcal antigen cross-reacts with synovial fluid?
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A child presents with an infective skin lesion. The test to confirm the organism is:
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Treatment for streptococcal necrotizing fasciitis includes:
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For an outbreak of Streptococcal Pharyngitis, the transport media of choice would be:
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Streptococcal toxic shock syndrome is due to what virulence factor?
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The commonest organism causing cellulitis is:
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All are true about Streptococcus except:
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Group A hemolytic pharyngitis is due to:
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A child presents with sepsis. The most probable organism is:
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Neonatal meningitis acquired during passage through the birth canal is due to:
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Which of the following organisms shows positive CAMP test?
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Which group of streptococcus can grow at 60°C?
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Not true about Enterococcus:
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False about gram positive cocci is:
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A patient admitted to an ICU, after 7 days of antibiotics develops a spike of fever and blood culture is positive. The most likely organism causing the infection is:
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Which of the following organisms, when isolated in the blood, requires the synergistic activity of penicillin plus an aminoglycoside for appropriate therapy?
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A 45-year-old patient has intra-abdominal sepsis, resistant to multiple antibiotics. Which organism could it be?
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A patient developed infective endocarditis after dental extraction. Most likely organism causing this is:
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A sputum culture shows gram positive cocci in chains and alpha hemolytic colonies. Which test will help confirm the diagnosis?
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True regarding Streptococcus pneumoniae except:
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Study Notes
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.
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Description
Test your knowledge on Streptococcus bacteria with this NEET pattern based quiz. Understand the characteristics, classifications, and clinical implications of various strains such as Str. pyogenes, Str. pneumoniae, and Enterococcus. Perfect for medical exam preparation and microbiology enthusiasts.
