Studies on Micrococcus Fasteus, a New Micrococcal Species, Isolated from Human Skin Lesions

Many cases of staphylococcal infection resistant to antibiotic therapy have been successfully treated by the use of toxoid prepared from resistant Staphylococcus aureus strains in our laboratory. In recent one year, we have encountered occasional cases with skin lesions which do not respond to such toxoid therapy in spite of the fact that morphologically staphylococci-like microorganisms can be isolated from the corresponding lesions almost in pure state.We have collected 9 strains from patients with chronic, skin lesions which did not respond to both antibiotics and staphylococcal toxoid, and examined their detailed biological and serological properties in order to know the reason why they being resistant to such therapies.These cocci are spherical cells similar to staphylococci, but they are usually arranged in dipro or tetra forms and never be grouped in irregular clusters as often seen in Staphylococcus aureus or epidermidis. In addition, they are not uniform in size and tend to be somewhat larger than staphylococci. For these reasons they are not so difficult to identify from staphylococci by simple microscopic examination of directstained smears from the lesions or their cultures.Their biological properties are quite similar to those of staphylococci except for being incapable of producing nitrite from nitrate. They are variable in the coagulase test and almost all strains are resistant to the antibiotics, particularly to penicillin. Their colonies on agar media are also similar in appearance to those of staphylococci and cannot be identified by simple inspection.A soluble, thermolabile exotoxin is produced by them which causes tissue necrosis or death in experimental animals and heamolyzes rabbit erythrocytes. This exotoxin is antigenic like staphylococcal exotoxin and gives rise to a specific antitoxin which neutralyzes it, and can be altered to toxoid form by treatment with formalin according to the method used for preparation of staphylococcal toxoid.We have prepared M. fasteus toxoid adopting the representative strains and applied it to clinical cases for therapeutic purpose of chronic skin lesions uncontrollable by antibiotics or staphylococcal toxoid which proved capable of inducing complete disappearance of M. fasteus in a short period, which was followed by the rapid healing of the skin lesions.