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 

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