staph

• Staphylococcus


  Spherical cells arranged in irregular clusters
• Micrococcus


  Gram-positive cocci, similar to Staphylococcus
• Sir Alexander Ogston established the causative role of the coccus in abscesses and other suppurative lesions


  1880
• von Recklinghausen first observed Staphylococcus in human pyogenic lesions


  1871
• Staphylococcus


  Name given by Ogston due to the typical occurrence of the cocci "in grape-like clusters" in pus and in cultures
• Common isolates of gram-positive cocci in clinical microbiology laboratory

  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus
  • Staphylococcus lugdunensis
  • Staphylococcus haemolyticus
• Classification of Staphylococcus species

  • Coagulase-positive staphylococci
  • Coagulase-negative staphylococci (CONS)
• Coagulase-positive staphylococci


  Includes Staphylococcus aureus
• Coagulase-negative staphylococci (CONS)


  Includes Staphylococcus epidermidis and Staphylococcus saprophyticus
• Staphylococci are a normal component of man's indigenous microflora and are carried asymptomatically in a number of body sites
• About 10-30% of healthy persons carry staphylococci in the nose, about 10% in the perineum, and about 5-10% in the vagina (which rises greatly during menses)
• Staphylococci


  • Spherical cells arranged in irregular clusters
  • Appear singly, in pairs, gram-positive
  • Exhibit spherical cells (0.5 to 1.5 µm)
  • Lack spores and flagella, may have capsules, and are catalase-positive
• Staphylococci


  • Nonmotile, non-spore-forming, and aerobic or facultatively anaerobic
  • Colonies are medium-sized (4 to 8 mm), cream-colored, white or rarely light gold, and "buttery-looking"
  • Rare strains are fastidious, requiring carbon dioxide, hemin, or menadione for growth
  • Some species are β-hemolytic
• Staphylococci resemble some members of the family Micrococcaceae, such as the genus Micrococcus
• Other gram-positive cocci occasionally recovered from human clinical specimens include Rothia mucilaginosa, Aerococcus, and Alloiococcus otitis
• Coagulase-producing (coagulase-positive) staphylococci


  • S. aureus
  • S. intermedius
  • S. pseudintermedius
  • S. hyicus
  • S. delphini
  • S. lutrae
  • S. agnetis
  • Some strains of S. schleiferi
• S. lugdunensis and S. schleiferi are sometimes mistaken for coagulase-positive staphylococci because of the presence of clumping factor
• Majority of clinical staphylococcal isolates identified by the tube coagulase test will be S. aureus
• Coagulase-negative staphylococci (CONS or non-Staphylococcus aureus) species


  • Novobiocin susceptible group: S. Epidermidis, S. Capitis, S. Haemolyticus, S. Hominis subsp. Hominis, S. Lugdunensis, S. Saccharolyticus, S. Warneri, and other species
  • Novobiocin resistant group: S. Cohnii, S. Kloosii, S. Saprophyticus, and S. Xylosus
• Purulent exudates, joint fluids, aspirated secretions, and other body fluids should be cultured regardless of the results of the microscopic examination, as the genus or species cannot be appropriately identified
• Aspirate is the best sample, a single swab would be less satisfactory for both culture and smear results
• Microscopic examination of Staphylococci

  • Spherical cocci, approximately 1 µm in diameter, arranged in grape-like clusters
  • May also be found singly, in pairs and in short chains of three or four cells
  • Non spore forming, non motile and usually non capsulated
  • Stain readily with aniline dyes and are uniformly gram-positive
• Staphylococci grow easily on routine laboratory culture media
• Selective media for heavily contaminated specimens

  • Mannitol Salt Agar (MSA)
  • Columbia Colistin–nalidixic Acid Agar (CNA)
  • Phenylethyl Alcohol (PEA) agar
• Mannitol Salt Agar (MSA)


  High NaCl concentration (7.5%) makes this medium selective for Staphylococcus, incorporation of mannitol and phenol red distinguishes S. aureus from most CoNS
• CHROMagar Staph aureus


  Selective and differential medium for isolation and identification of S. aureus
• CHROMagar MRSA


  Can further classify S. aureus into MRSA or methicillin susceptible Staphylococcus aureus (MSSA) strains
• Appearance on CHROMagar


  • Staphylococcus aureus → pink to mauve
  • Other bacteria → Colourless, blue or inhibited
• Appearance on Sheep Blood Agar (SBA) or Blood Agar Plate (BAP)

  • Produce round, smooth, white, creamy colonies after 18 to 24 hours of incubation
  • Can produce hemolytic zones around the colonies
  • Rarely exhibit pigment production (yellow) with extended incubation
• Staphylococci


  • Aerobes and facultative anaerobes
  • Optimum pH is 7.5
  • Can grow readily on ordinary media
• Small colony variants (SCVs) of Staphylococci

  • Grow as nonpigmented, nonhemolytic pinpoint-size colonies mixed with colonies exhibiting the normal phenotype
• Staphylococcus epidermidis colonies


  • Usually small- to medium-sized, nonhemolytic, gray-to-white
• Staphylococcus saprophyticus colonies


  • Slightly larger, about 50% produce a yellow pigment
• Staphylococcus haemolyticus colonies


  • Medium-sized, with moderate or weak hemolysis and variable pigment production
• Staphylococcus lugdunensis colonies

  • Often hemolytic and medium sized, although small colony variants can occur
• Oxidation-fermentation (O/F) reactions do not sufficiently discern certain weak acid producers, such as Micrococcus kristinae, and staphylococci that fail to grow or produce acid anaerobically
• Microdase Disk

  Used to rapidly differentiate staphylococci from micrococci, most staphylococci test negative, micrococci test positive
• Molecular testing, plasmid typing, fatty acid analysis, and matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) have been used for species and strain identification
• Catalase test

  Demonstrates the presence of catalase, an enzyme that catalyses the release of oxygen from hydrogen peroxide (H2O2), to distinguish Staphylococci spp. and Micrococci spp.
• Coagulase test

  Clumping factor (cell-bound coagulase) causes agglutination in human, rabbit, or pig plasma, directly converts fibrinogen to fibrin, which precipitates onto the cell surface, causing agglutination