DrySpot™Staphytect Plus™Latex Agglutination Test

DrySpot Staphytect Plus latex agglutination test uses blue latex particles, which are coated with porcine fibrinogen and rabbit IgG, then pre-dried onto reaction cards for the detection of clumping factor, Protein A, and capsular polysaccharides of S. aureus.

• Long shelf-life: two years from the date of manufacture
• Flexible storage: can be stored in a fridge or at room temperature (2-25°C)
• No dispensing errors: reagents are pre-dried onto reaction cards
• Easy-to-read blue latex
• Rapid results: within 20 seconds
• Excellent sensitivity: detects three properties of S. aureus for wider strain identification

Traditionally, differentiation between coagulase-positive and coagulase-negative staphylococci has been performed either with the tube coagulase test that detects extracellular staphylocoagulase or the slide coagulase test that detects the clumping factor (bound coagulase) present on the bacterial cell surface. It has been reported that approximately 97% of human strains of S. aureus possess both bound coagulase and extracelluar staphylocoagulase. Protein A is found on the cell surface of about 95% of human strains of S. aureus and has the ability to bind the Fc portion of immunoglobulin G (IgG)¹.

Certain methicillin-resistant strains of S. aureus (MRSA) may express undetectable levels of clumping factor and Protein A^2,3,4. It has been shown, however, that these strains possess capsular polysaccharide⁵. The capsule can mask both Protein A and the clumping factor, thereby, preventing agglutination.

DrySpot Staphytect Plus uses latex particles coated with porcine fibrinogen and rabbit IgG, including specific polyclonal antibodies raised against capsular polysaccharides of S. aureus^6,7. When the dried reagents are mixed with a suspension of S. aureus colonies, rapid agglutination occurs through the reaction between (i) fibrinogen and clumping factor, (ii) the Fc portion of IgG and Protein A, (iii) specific IgG and capsular polysaccharide.

Agglutination may also occur with other species which possess clumping factor or Protein A, such as Staphylococcus hyicus and Staphylococcus intermedius. If neither clumping factor, Protein A, or specific capsular polysaccharides are present, agglutination will not occur, and the result will be regarded as negative. The most frequent coagulase and Protein A negative isolates of staphylococci are Staphylococcus epidermidis.

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