The lipase test was examined for usefulness as an aid in the identification of pathogenic staphylococci, with special reference to the sort of substrates used. It was compared with the egg-yolk test with regard to interrelationships among coagulase, deoxyribonuclease DNase and other biological attributes.
The test strains employed consisted of 577 coagulase-positive and 150 coagulase-negative staphylococcal strains freshly isolated from human and swine clinical materials. The basic media used were Gillespie's agar, Starr's agar, heart infusion agar and, as control, egg-yolk agar. Several oils and Tween 20 and 80 were employed as substrates. The results obtained are as follows.
All the test strains of human origin showed the closest correlation between the coagulase and DNase activity production like those in the preceding investigation. The results of the egg-yolk test were inferior to those of the DNase test with regard to coagulase production when both tests were performed with media containing various oils. The correlation between the coagulase and lipase activities was very high as to the coagulase-positive strains, but considerably low in identity as to the coagulase-negative ones. The heart infusion agar containing Tween 80, however, gave a relatively good result in this point. Especially, the oil or Tween media supplemented with the egg-yolk protein fraction, which had beed devised by the authors, behaved in almost the same fashion as the egg-yolk medium.
Therefore, it may be conculuded that the medium containing Tween 80 and egg-yolk protein is the most appropriate for testing the lipase activity of staphylococci, considering the enzyme specificity.
It should be noted that the strains of swine origin, both coagulase-negative and coagulase-positive, showed a better interrelationship among the lipase, egg-yolk, and coagulase tests than those of human origin.