Streptococcus species

General Properties of ALL Streptococci

  • Gram staining properties:

    • Gram positive cocci in chains/pairs

      • DDx: Gram positive cocci in clusters= Staphylococcus species.

      • DDx: Gram positive cocci in tetrads = Micrococcus species.

 

  • Special Lab Tests:

    • Catalase negative (ALL)

      • DDx: Catalase positive = Staphylococcus species.

    • Microaerophilic (ferments glucose, prefers reduced oxygen concentrations)

    • Hemolytic Testing (Blood Agar)

      • Alpha Hemolysis

        • Partial hemolysis of RBCs giving a green color

        • Types:

          • S. pneumoniae

          • Viridans strep

      • Beta Hemolysis

        • Complete hemolysis of RBC causing clearing/yellow around the organism

        • Types:

          • Group A Strep (S. pyogenes )

          • Group B Strep (S. agalactiae)

      • Gamma (NO) Hemolysis

        • No hemolysis  of RBC so colonies remain red (unchanged) on agar plate

        • Types:

          • Enterococcus

          • Group D Strep (S. bovis/ S. gallolyticus)

 

 

 

Alpha Hemolysis

Streptococcus pneumoniae

  • Unique Identifying Features:

    • Alpha Hemolysis

    • Optochin (P disk) susceptible

      • P disk= strep Pneumo (don't confuse "P" on the antibiotic disk for Penicillin, although S. pneumo does have an acquired resistance to penisillin as well... tricky!)

    • Bile susceptible

    • Quellung reaction (detects capsule)

 

  • Virulence factor:

    • Polysaccharide capsule (detected via Quellung reaction)

    • Acquired resistance to Penicillin due to altered PBP (penicillin binding protein)

 

  • Clinical Syndromes:

    • Causes the most serious infections in infants (<2  yrs) and elderly populations

    • Pneumonia

      • Major cause of Community acquired pneumonia

      • Causes lobar consolidation

    • Meningitis

      • Most common cause in infants/toddlers/adults

    • Spontaneous bacterial peritonitis (in cirrhotic patients)

 

Viridans Streptococci

  • General info:

    • Normal florof upper respiratory & urogenital tracts

    • Variable susceptibilities

 

  • Subtypes:

    • S. mutans

    • S. salivarius

    • S. sanguis

    • S. mitis

    • S. anguinosus group (S. anginosus, S. consellatus, S. intermedius)

      • more virulent

    • Abiotrophia & Granulicatella 

      • see below... used to be called "Nutritionally deficient Strep"

 

  • Unique Identifying Features:

    • Alpha Hemolysis

    • Optochin (P disk) resistant

    • Bile resistant

 

  • Clinical Syndromes:

    • Causes 30-40% of cases of subacute bacterial endocarditis in those with pre-existing native valvular disease

 

Abiotrophia & Granulicatella (Used to be called "Nutritionally Deficient Streptococcus")

  • General Features:

    • Member of Viridans group

    • Normal flora of upper respiratory, urogenital & GI tracts.

    • Need to be aware because this is MORE RESISTANT TO ANTIBIOTICS THAN OTHER VIRIDANS STREP!

 

  • Unique Identifying Features:

    • Require cysteine or pyridoxal to grow (will not grow on blood agar)

      • To do this, you streak S. aureus on a plate with cysteine containing media. The nutrients from Staph aureus will allow the nutritionally deficient strep to grow around it. Thus will see growth surrounding the streak of S. aureus.

    • PYR TESTING POSITIVE

 

  • Clinical Features:

    • Endocarditis

 

 

Beta Hemolysis

 

Streptococcus pyogenes (Group A Strep)

  • Unique Identifying Features:

    • Beta Hemolysis

    • Bacitracin susceptible

    • PYR testing positive

      • DDx: Enterococcus is also PYR positive, but it is Bacitracin RESISTANT and can grow in BILE or 6.5% NaCl

 

  • Clinical Syndromes:

    • Pharyngitis

    • Meningitis

    • Skin/Soft tissue infections

      • Cellulitis

      • Impetigo

      • Eryspielas

      • Myositis

      • Necrotizing fasciitis

      • Pneumonia

    • Streptococcal toxic shock syndrome

      • Usually begins with soft tissue infection

      • Elaborate pyrogenic exotoxins

    • Sequelae/Complications of untreated Strep infection

      • Rheumatic fever

      • Glomerulonephritis

 

  • Virulence factors:

    • M protein

    • Capsule- hyaluronic acid

    • Streptolysin O (oxygen labile)

    • Streptolysin S (oxygen Stable)

    • Streptococcal pyrogenic exotoxins

 

Streptococcus agalactiae (Group B Strep)

  • General info:

    • Affect mostly babies or old people.

    • Neonatal/perinatal disease

      • Due to vertical transmission (in utero or during delivery)

      • Pregnant women should be screened at 35-37 weeks using enrichment methods (LIM, carrot broth) to determine GBS carriage so can prophylactically treat baby.

      • Disease presents early in neonatal period (<7 days) or late (7-28 days)

 

  • Unique Identifying Features:

    • Beta Hemolysis

    • CAMP test positive

    • Hippurate positive

 

  • Clinical Syndromes:

    • Affect mostly babies or old people.

    • Neonatal/perinatal disease

      • Meningitis

    • Elderly diseases

      • Bacteremia

      • Meningitis

      • UTI

      • Soft tissue infections

 

​​

 

 

Gamma (NO) Hemolysis

 

Enterococcus

  • General Features: ​​

    • Normal flora of GI/biliary tracts, vagina & male urethra.

    • 2nd most common cause of nosocomial infections in US.

 

  • Types:

    • E. faecalis (80-90%

    • E. faecium (10-15%)

 

  • Unique Identifying Features:

    • Gamma (NO) Hemolysis

    • Bile Esculin positive

    • 6.5% NaCl testing POSITIVE

      • DDx: S. bovis/gallolyticus is NEGATIVE

    • PYR TESTING POSITIVE

      • DDx: Group A strep (S. pyogenes) is also PYR positive, but it is BACITRACIN sensitive and does NOT grow in Bile or NaCl.

      • DDx: S. bovis/gallolyticus is NEGATIVE

​​​

  • Clinical Syndromes: ​​

    • UTI
    • Bacteremia

    • Endocarditis

    • Abdominal/Pelvic infections

    • Soft tissue infections

 

  • Virulence factors/Resistance Issues: ​​

    • Aminoglycoside resistance

    • High MICs for Penicillins

    • Vancomycin resistance (VRE)

 

Streptococcus bovis/ Streptococcus gallolyticus

  • Unique Identifying Features:

    • Gamma (NO) Hemolysis

    • Bile Esculin positive

    • 6.5% NaCl testing NEGATIVE

      • DDx: Enterococcus is POSITIVE

    • PYR TESTING NEGATIVE

      • DDx: Enterococcus is POSITIVE

    • Penicillin susceptible

 

  • Clinical Features:

    • Bacteremia and endocarditis ​​

    • ASSOCIATED WITH COLON CANCER!!

 

 

 

 DDx: Other Gram Pos cocci similar to Strep...

 

Abiotrophia & Granulicatella (Used to be called "Nutritionally Deficient Streptococcus")

  • General Features:

    • Member of Viridans group

    • Normal flora of upper respiratory, urogenital & GI tracts.

    • Need to be aware because this is MORE RESISTANT TO ANTIBIOTICS THAN OTHER VIRIDANS STREP!

 

  • Unique Identifying Features:

    • Require cysteine or pyridoxal to grow (will not grow on blood agar)

      • To do this, you streak S. aureus on a plate with cysteine containing media. The nutrients from Staph aureus will allow the nutritionally deficient strep to grow around it. Thus will see growth surrounding the streak of S. aureus.

    • PYR TESTING POSITIVE

 

  • Clinical Features:

    • Endocarditis

 

Aerococcus

  • General Features:

    • Often confused with Enterococcus & Viridans Strep

    • Gram-stain= Gram positive cocci in tetrads or clusters

 

  • Unique Identifying Features:

    • Alpha Hemolysis

 

  • Clinical Features:

    • Causes opportunistic infections (endocarditis, meningitis, arthritis, UTI)

 

Leuconostoc

  • General Features:

    • Gram-stain= Gram positive cocci in chains

    • VANCOMYCIN RESISTANT

 

  • Unique Identifying Features:

    • Alpha Hemolysis

 

  • Clinical Features:

    • Causes infections in immunocompromised hosts- bacteremia, catheter infections, meningitis

 

Pediococcus

  • General Features:

    • Gram-stain= Gram positive cocci in clusters/ tetrads

    • VANCOMYCIN RESISTANT

 

  • Clinical Features:

    • Causes infections in immunocompromised hosts

 

Gemella

  • General Features:

    • Normal flora of upper respiratory & GI tracts.

    • Infrequently isolated from clinical specimens

    • Sometimes mistaken for Viridans Strep.

 

​​

Streptococcus pyogenes (Group A Strep)

Streptococcus agalactiae (Group B Strep)

Streptococcus bovis (Group D Strep)

Streptococcus pneumoniae

Viridans Strep

Enterococcus

MICRO & IMMUNO 

INDEX

PREVIOUS TOPIC

NEXT TOPIC

  • Facebook - Black Circle
  • Twitter - Black Circle
  • Pinterest - Black Circle

DISCLAIMER: THIS WEBSITE DOES NOT PROVIDE MEDICAL ADVICE

These posts contain high yield information collected from various educational resources including textbooks, journal articles, educational websites and more. They are intended for educational use only and should NOT be taken as medical advice. I strongly believe the spreading of knowledge and depth of learned information should be encouraged in today's society rather than coveted. Membership is required to view these posts  and should be used solely for educational purposes only.