Streptococcus Classification and Characteristics

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Questions and Answers

What is the arrangement of pneumococci in a Gram stain?

Long chains
Short chains
Single cells
Pairs (diplococcic) (correct)

What is the type of hemolysis exhibited by pneumococci on blood agar?

Beta hemolytic
Gamma hemolytic
Alpha hemolytic (correct)
No hemolysis

What is a common predisposing factor for pneumococcal pneumonia?

Hypertension
Age > 65
Diabetes mellitus
Immuno-suppression (correct)

What is the characteristic arrangement of Gram positive cocci?

In chains or pairs (D) Signup and view all the answers

What is the typical source of pneumococcal infections?

Nasopharynx carrier (C) Signup and view all the answers

Which of the following is a virulence factor of Streptococcus pyogenes?

M protein (A) Signup and view all the answers

What is the characteristic feature of pneumococcal colonies on blood agar?

Alpha hemolysis (A) Signup and view all the answers

What is the characteristic of Streptococcus pyogenes on Blood agar?

Small, beta-hemolytic colonies (C) Signup and view all the answers

What is the purpose of the optochin test in the identification of pneumococci?

To confirm pneumococcal identification (B) Signup and view all the answers

What is the function of Streptokinase?

To convert plasminogen to plasmin (D) Signup and view all the answers

Why are enterococci not classified with streptococci?

They grow at 45°C and are salt tolerant (B) Signup and view all the answers

Which of the following is NOT a type of Streptococcus?

S. aureus (B) Signup and view all the answers

What is the typical manifestation of pneumococcal meningitis?

Inflammation of the meninges (D) Signup and view all the answers

What is the function of Hyaluronic acid capsule?

To protect the bacteria from phagocytosis (D) Signup and view all the answers

Which classification system is used to classify Streptococci based on the presence of polysaccharide and teichoic acid antigens?

Lancefield classification (C) Signup and view all the answers

What is the characteristic of Streptococcus pyogenes in terms of hemolysis?

Beta-hemolytic (C) Signup and view all the answers

What is the characteristic of Streptolysin O?

Oxygen labile and causes beta-hemolysis on blood agar (A) Signup and view all the answers

What is the characteristic of Streptolysin S?

Oxygen stable and does not cause complete lysis of red blood cells on blood agar (C) Signup and view all the answers

What is the disease caused by Streptococcus pyogenes that is characterized by fever, rash, and scarlet fever?

Scarlet fever (C) Signup and view all the answers

What is the type of infection caused by Streptococcus pyogenes in the fetus after delivery or abortion?

Puerperal sepsis (B) Signup and view all the answers

What is the symptom of Scarlet fever?

All of the above (D) Signup and view all the answers

What is the disease caused by Streptococcus pyogenes that is characterized by an organ failure?

Toxic shock syndrome (C) Signup and view all the answers

What is the laboratory diagnosis of Streptococcus pyogenes?

All of the above (D) Signup and view all the answers

What is the disease caused by Streptococcus pyogenes that is characterized by migrating polyarthritis?

Acute rheumatic fever (A) Signup and view all the answers

What is the primary source of specimens for identification of S. agalactiae?

Uterine swab (C) Signup and view all the answers

What is the characteristic arrangement of S. agalactiae under a microscope?

Chain (C) Signup and view all the answers

What is the primary disease caused by S. viridans?

Dental caries (D) Signup and view all the answers

What is the purpose of the Bacitracin test in identifying S. agalactiae?

To identify the bacteria's sensitivity to Bacitracin (A) Signup and view all the answers

What is the recommended treatment for pregnant women with S. agalactiae infection?

Intravenous ampicillin (D) Signup and view all the answers

What is the characteristic of the colonies formed by S. agalactiae on blood agar?

Beta hemolytic (C) Signup and view all the answers

What is the type of hemolysis caused by S. viridans?

Alpha hemolytic (D) Signup and view all the answers

What is the primary method of preventing neonatal infections caused by S. agalactiae?

Screening of pregnant women and treatment if necessary (D) Signup and view all the answers

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Study Notes

Gram Positive Cocci

Gram positive cocci include Streptococcus and Enterococcus
Arranged in chain or pairs
Facultative anaerobes
Grow in enriched media
Catalase negative (-)
No spore, no motile

Streptococcus

More than 50 species, the most important are:
- S. pyogenes
- S. agalactiae
- S. viridans
- S. pneumoniae
Classified based on hemolysis on Blood agar:
- Beta hemolysis (S. pyogenes, S. agalactiae)
- Alpha hemolysis (S. pneumonia)
- No hemolysis (S. bovis)
Classified based on Lancefield classification:
- Streptococcus Pyogenes (Group A) beta hemolytic

Streptococcus Pyogenes

Culture: Facultative anaerobes grow in Blood agar at 37°C for 24h in clear hemolytic small colonies
Virulence factors:
- Adherence (M protein)
- Hyaluronic acid capsule
- Streptokinase
- Streptolysin
- Pyrogenic exotoxins (A, B, C)
Diseases:
- Pyogenic local infection (pharyngitis, tonsillitis)
- Puerperal sepsis
- Acute endocarditis
- Scarlet fever
- Necrotizing fasciitis
- Streptococcal toxin shock syndrome
- Acute rhematic fever (RF)
- Acute glomerulonephritis

Lab Diagnosis of S. pyogenes

Specimen: according to the site of infection
Direct smear: Gram staining
Cultivation: on blood agar at 37°C for 24h
Identification: Beta hemolysis colonies on blood agar
Colonies identified by:
- Gram staining
- Catalase test: Neg (-)
- Bacitracin test: sensitive

S. agalactiae

Morphology & culture: Gram (+) cocci arranged in chain, capsulated, non-motile, non-spore forming
Culture: facultative anaerobes, grow in blood agar at 37°C for 24h
Diseases: neonatal pneumonia, neonatal septicemia, neonatal meningitis
Lab diagnosis:
- Cultivate a vaginal swab on blood agar at 37°C for 24h
- Identification: B hemolytic colonies
- Gram staining: G+ cocci arranged in chain
- Bacitracin test: Resistant
Treatment: intravenous ampicillin at least 4 hours prior to delivery

S. viridans

Morphology & culture: Gram (+) cocci arranged in chain, capsulated, non-motile, non-spore forming
Culture: facultative anaerobes, grow in blood agar at 37°C for 24h
Diseases: dental caries, subacute bacterial endocarditis
Lab diagnosis:
- Specimen from blood and do a blood culture
- Subculture on blood agar that gives a greenish alpha hemolytic colonies
- Gram staining
- Optochin test: Resistant

S. pneumoniae

Morphology & culture: Gram positive cocci arranged in Pairs (diplococcic), capsulated, non-motile, non-spore forming
Culture: facultative anaerobes grow on blood agar (alpha hemolytic)
Diseases: labor pneumonia, sinusitis, otitis media, meningitis
Lab diagnosis:
- Specimen from sputum for pneumonia, ear swab for otitis media, nasal swab for sinusitis, CSF for meningitis, blood for endocarditis
- Direct smear: Gram positive cocci in pairs (diplococcic)
- Cultivation: on blood agar at 37°C for 24h
- Identification: alpha hemolytic colonies on blood agar
- Gram staining
- Catalase test: Neg (-)
- Optochin test: sensitive
- Quelling reaction: swilling of capsule
- Bile solubility: clear in S. pneumonia (sensitive)

Enterococcus

General features of Enterococcus:
- Two medically important species: E. faecalis and E. faecium
- Gram positive cocci, arranged in short chain / pairs
- Facultative anaerobes
- Catalase negative (-)
- Grow at 45°C, salt tolerant (not in Streptococci)

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