Gram positive
Staphylococcus sp, coagulase negative (not S. aureus)

Deputy Editor-in-Chief: Debra Zynger, M.D.
Joshua A. Lieberman, M.D, Ph.D.

Topic Completed: 1 April 2018

Minor changes: 9 July 2020

Revised: 30 January 2019

Copyright: (c) 2018-2020, PathologyOutlines.com, Inc.

PubMed Search: Staphylococcus sp[TIAB] coagulase negative

Joshua A. Lieberman, M.D, Ph.D.
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Cite this page: Lieberman, J.A. Staph coagulase negative. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/microbiologystaphylococcus.html. Accessed August 6th, 2020.
Definition / general
  • Gram stain: positive
  • Morphology: cocci in clusters
  • Facultative anaerobe
  • Part of normal flora of the skin and mucus membranes
Essential features
  • Unlike S. aureus, coagulase test is negative
  • Greek for staphyle ("bunch of grapes") and kokkos ("berry") (Emerg Infect Dis 2013;19:1553)
  • Coagulase negative staphylococci (CoNS)
  • Many recognized species
  • Important species include Staphylococcus epidermidis, S. saprophyticus, S. lugdunensis and S. haemolyticus
  • Common contaminants; to distinguish from true infection rely on clinical judgment, patient features (e.g. hematologic malignancy / immunosuppression) and number / site (central venous catheter vs. venipuncture) of positive cultures (Eur J Clin Microbiol Infect Dis 2012;31:2639, Clin Infect Dis 2004;39:333)
  • Biofilm formation and adherence to indwelling devices, catheters
  • Culture conditions
    • Blood agar plates (nonselective)
    • Enrichment broth (tryptic soy broth) in parallel increases culture yield / organism recovery
    • Chromogenic agars
    • Temperature: 34 - 37 °C, with most species producing growth within 24 hours; a few CoNS, such as S. lentus, may require up to 36 hours for colonies to appear
  • Gram positive
  • Catalase positive
  • Coagulase negative
  • Readily identified by matrix associated laser desorption ionization - time of flight mass spectrometry (MALDI-TOF MS)
    • MALDI-TOF MS is an increasingly essential tool in the clinical microbiology laboratory for rapid detection of microorganisms
  • Small colony variants (SCV) (Clin Microbiol Rev 2016;29:401)
    • Especially S. epidermidis, S. capitis and S. warneri
    • SCVs more often in foreign body associated infections, chronic or relapsing infections
    • Represent metabolic changes, adaptation to intracellular growth
  • Ferment fructose
  • S. saprophyticus resistant to novobiocin
  • Beta lactamase resistance and methicillin resistance are widespread
    • Vancomycin for methicillin resistant
    • Nafcillin for methicillin susceptible
    • Presence of mecA and altered PBP2a (penicillin binding protein)
  • High rates of resistance to fluoroquinolones, clindamycin, aminoglycoside and macrolides in hospital associated strains; linezolid resistance rare (Antimicrob Agents Chemother 2014;58:1404)
Clinical images

Contributed by Joshua A. Lieberman, M.D., Ph.D.

Chocolate agar

Gross description
  • Colonies typically small, beige to white
  • Variable hemolysis, depending upon species
Microscopic (histologic) description
  • Gram positive cocci in clusters, similar to other staphylococci
Microscopic (histologic) images

Contributed by Joshua A. Lieberman, M.D., Ph.D.

Gram stain

Molecular / cytogenetics description
  • Commercial polymerase chain reaction (PCR) based methods, including mecA detection (J Clin Microbiol 2013;51:2072)
  • Broad range 16S PCR followed by sequencing and bioinformatic identification
Differential diagnosis
  • Primarily other staphylococci
  • Aerococcus
  • Micrococcus
    Board review style question #1
    Most concerning mechanism of antibiotic resistance in the organism shown in the Gram stain below is:
    1. Altered penicillin binding protein
    2. Extended spectrum beta lactamase production
    3. Mutation in DNA gyrase
    4. Point mutation in the ribosomal 23S rRNA gene
    5. Porin mutation
    Board review answer #1
    A. Altered penicillin binding protein. The image shows Gram positive cocci in clusters. PBP2a, an altered (low affinity) penicillin binding protein, is the product of the mecA gene, and mediates oxacillin / methicillin resistance in staphylococci. Answer B is incorrect because although many Staphyloccoci strains are resistant to a variety of beta-lactam antibiotics, the extended spectrum beta lactamases (ESBLs) are a specific class of enzymes that destroy a wide range of beta-lactam antibiotics, and these are found in Gram-negative pathogens, particularly Enterobacteriaceae. Answer C is incorrect because mutations in DNA gyrase confer resistance to quinolone / fluoroquinolone antibiotics. Answer D is incorrect because point mutations in the 23S rRNA gene confer macrolide resistance, especially in Helicobacter pylori, by altering drug binding sites. Answer E is incorrect because porins are outer membrane proteins only found in Gram negative organisms. Porin mutations can block or reduce drug influx and drug effect; examples include Acinetobacter baumanii and imipenem and Pseudomonas aeruginosa and tobramycin.
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