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)

 

• Review the post for the FULL LABORATORY WORKUP OF GRAM POSITIVE COCCI for more details.

 

 

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 flora of 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

 

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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

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• 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.

 

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