Studies on Unique Staphylococcal Strains Exhibiting High Virulence for Mice by Intraperitoneal Inoculation

In the previous paper the authors reported that of 395 strains of staphylococcus freshly isolated from the various clinical specimens, eight strains were coagulase-negative but deoxyribonuclease-positive; particularly, the E 46 and E 97 strains were very stable in DNase production without any decrease by successive transfers and exhibited a high virulence for mice by intraperitoneal inoculation.In an attempt to clarify the mechanisms of action of these two strains in experimental infections, the authors investigated their morphological and biological properties in detail in comparison with the two strains of each typical species of Staphylococcus aureus and S. epidermidis, which were also simultaneously isolated. The following results were obtained.The E 46 and E 97 strains were almost identical with each other in every attribute with a slight difference of grade in biological activities. The distinctive characters of the both strains were as follows:Circular, smooth, glistening colonies on heart-infusion agar. Diffuse colonies in serum soft agar. Capsule-like structure observed. Ribitol and anhydroribitol demonstrated. Coagulase-negative in both tube and slide tests. DNase-positive. Lysozyme-positive. Egg-yolk test positive. Fibrinolysin-positive. Phenolphthalein phosphatase produced. Trace of or no α-lysin produced. Acid from mannitol. In addition the strains E 46 and E 97 proved sensitive to a variety of antibiotic but resistant to sulfa (sulfisoxazole).From all the results obtained, these strains may be regarded as a very unique staphylococcus that possesses the intermediate characters between those of S. aureus and S. epidermidis and also as a special type of S. aureus losing an ability of coagulase-production.The authors also discussed on the current classification method for staphylococcus in view of appearance of such unique strains which are coagulase-negative but DNase-positive and highly virulent for mice.