General Properties of ALL Staphylococci

• Gram staining properties:

  • Gram positive cocci in clusters  

    • DDx: Gram positive cocci in chains = Streptococcus species.

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

 

• Special Lab Tests:

  • Catalase positive (ALL)

    • DDx: Catalase negative = Streptococcus species.

  • Facultative Aerobe (ferments glucose, prefers oxygen)

  • Coagulase testing

    • Positive

      • S. aureus

      • **S. lugdunensis (is POS in SLIDE coag testing, but NEG in TUBE coag testing)

    • Negative

      • All other staphylococcus (commonly referred to as Coag-negative staph)

 

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

 

Staphylococcus aureus 

• Unique Identifying Feature:

  • Coagulase positive (all other staph are negative)

  • Turns the pink media yellow on agar plate

 

• Virulence factors:

  • Protein A

  • Capsular polysaccharides

  • Coagulase enzyme

  • Toxins (TSST-1, enterotoxins)

  • Hemolysins

    • NOTE: S. haemolyticus also has hemolytic properties, but is COAG NEGATIVE

 

• Clinical Presentation & Diseases:

  • Toxic shock syndrome (TSST-1 toxin)

  • Scalded skin syndrome (SSS)- due to Exfoliatin

  • Soft tissue infections- due to Panton Valentine Leukocidin (PVL)

  • Food poisoning- Enterotoxins

  • Bacteremia & Endocarditis

 

• Methicillin Resistant Staph Aureus (MRSA) 

  • Virulence factors: Altered penicillin binding protein (PBP) produced by the  mecAgene .

 

Staphylococcus epidermidis 

• General Features:

  • Most frequently isolated (often a contaminant)

 

• Virulence factors:

  • Produces extracellular slime layer (biofilm)

 

• Clinical Presentation & Diseases:

  • Endocarditis, particularly prosthetic valves

 

Staphylococcus saprophyticus 

• Unique Identifying Feature:

  • Differentiation from other staph organisms= Novobiocin resistant

    • Most other Staph are susceptible to Novobiocin

 

• Clinical Presentation & Diseases:

  • Acute UTI in young, sexually active women

    • 2nd most common cause of cystitis

 

Staphylococcus  haemolyticus

• Virulence factors:

  • Has hemolytic properties

    • Do NOT confuse with S. aureus which is COAGULASE POSITIVE

  • Is intrinsically resistant to Vancomycin

    • Do NOT confuse with Vancomycin resistant Enterococcus (VRE) which is gram pos cocci in CHAINS (Strep species).

 

• Clinical Presentation & Diseases:

  • Line related sepsis

 

Staphylococcus  lugdunensis

• General Features:

  • Is Coagulase positive on the SLIDE, but Coagulase negative in the TUBE Testing

  • PYR reaction differentiates it from S. aureus

 

 

DIFFERENTIAL DIAGNOSIS

Staphylococcus species

• General Features:

  • Gram positive cocci in chains/pairs  

• Lab Tests:

  • ​Catalase NEGATIVE

 

Micrococcus species

• General Features:

  • Gram positive cocci in tetrads

  • Normal flora of skin and mucous membranes

    • Rarely causes infection, so don't confuse with Staph!! 

• Lab Tests:

  • Microdase test + (modified oxidase reaction)

  • Forms yellow colonies (similar to Staph aureus)

  • Does NOT ferment glucose (staph does)

 

Rothia mucilaginosa (formerly Stomatococcus mucilaginosus)

• General Features:

  • Large Gram positive cocci in pairs or clusters

  • Normal flora of skin and oral cavity

  • Pathogen in patients with underlying malignancy/ bone marrow transplant

    • Central lines

    • Endocarditis

    • Bacteremia 

• Lab Tests:

  • Colonies are sticky or mucoid, white and adherent to the agar

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