Coagulase test

Used to differentiate Staphylococcus aureus from less pathogenic coagulase-negative staphylococci
Tests for the ability of the organism to convert fibrinogen into fibrin (that is, to form a clot)
Slide coagulase
- Checks for agglutination after a drop of plasma is combined with a suspension of the bacteria on a slide
- Positive if clumping is apparent within 10 seconds or less, and no clumping is observed in saline or water
- A few species of coagulase-negative staphylococci may be positive due to membrane-bound clumping factor
  - Staphylococcus lugdenensis, Staphylococcus schleiferi subsp. schleiferi, Staphylococcus sciuri subsp. carnaticus, Staphylococcus sciuri subsp. rodentium, and Staphylococcus intermedius
- Staphylococcus aureus is negative in 15% of tests, especially MRSA, so negative results need to be confirmed with tube coagulase
Tube coagulase
- Mix a heavy inoculum of bacteria into a tube filled with rabbit plasma
- Positive if clot is formed within 4 hours when incubated at 37ºC
- A few species of Coagulase-negative staphylococci may be positive: Staphylococcus intermedius, Staphylococcus saccharolyticus, and Staphylococcus schleiferi

References

^ Takashi Sasaki, Sae Tsubakishita, Yoshikazu Tanaka, Arihito Sakusabe, Masayuki Ohtsuka, Shintaro Hirotaki, Tetsuji Kawakami, Tsuneo Fukata, Keiichi Hiramatsu. Multiplex-PCR Method for Species Identification of Coagulase-Positive Staphylococci. Journal of Clinical Microbiology. 2010;48(3):765-769. doi:10.1128/jcm.01232-09.