EVIDENCE AGAINST THE INVOLVEMENT OF MYCOBACTERIUM ULCERANS IN MOST CASES OF NECROTIC ARACHNIDISM

Cutaneous lesions caused by M. ulcerans were shown to bear only a supe rficial resemblance to those produced by certain spider species. M. ul cerans was not found in either the venoms or the midguts of several Au stralian spiders, and deliberate contamination by inoculation of the f angs and digestive system of the wolf spider, Lycosa godeffroyi, did n ot result in permanent colonization. M. ulcerans was successfully intr oduced into the skin of mice through a small trauma site similar to th at caused by a spider bite. However, because M. ulcerans was shown to survive on exposed surfaces for only a short period, a successful inoc ulation is likely only if the skin is contaminated with this organism after, or at the same time as, the skin suffers damage. The claim by o ther workers that M. ulcerans produces cutaneous ulcers by release of an exotoxin could not be confirmed. The authors conclude that M. ulcer ans is not involved in most cases of necrotic arachnidism and hence th ere is no justification for prescribing anti-mycobacterial antibiotics to resolve alleged spider bite lesions unless the presence of M. ulce rans has been demonstrated by appropriate laboratory tests.