Mycobacterium chelonae y Mycobacterium abscessus: patógenos emergentes

Abstract

A mycobacterium isolated in 1903 from the lungs of a sick marine turtle was the first report of Mycobacterium chelonae. It is a different species from Mycobacterium fortutuitum, isolated from frogs in 1905, and from Mycobacterium abscessus which was initially considered a subspecies of M. chelonae. Within the group of rapidly growing mycobacteria, which are characterized by their growth in culture in less than 7 days, these three species are the only human pathogens of the species. They are causative agents of localized or disseminated subcutaneous nodules and abscesses, of postoperative lesions, osteomielitis, queratitis and several other lesions. Skin and soft tissue lesions are most frequently observed, produced by the traumatic inoculation of these mycobacteria. Histopathology of nodules and abscesses reveals a mixed inflammatory, supurative and granulomatous process. In one quatier of these cases, clumps of acid fast bacilli can be demonstrated, usually localized within a vacuole at the centre of an abscess. Several outbreaks of subcutaneous abscesses produced by atypical mycobacteria, secondary to the application of contaminated injections, have been reponed in Colombia. In 1981, 50 people -mostly, children- were affected after vaccination against yellow fever in Bucaramanga; in 1989, 13 people were affected after subcutaneous allergen injections in Medellin. A third one involved 297 people, in 1993, along the Atlantic coast after the application of xilocayne subcutaneously for bioenergetic therapy. Other postraumatic cases have also been reported. The disseminated disease caused by mycobacteria of rapid growth occurs in immunosuppressed patients. Polymorphonuclears predominate in skin biopsies, no epithelioid granuloma is obsetved and abundant bacilli can be demonstrated in histological sections. The causative mycobacteria can be isolated from biopsies of lesions, since the precise diagnosis requires the accurate identification of the microrganism by culture. The practice of antibiograms is recommended dueto the varying differences in antimicrobial sensitivities among these mycobacteria. M. abscessus is sensitive to clarithromycin, amikacyn and cefoxitim; M. fortuitum to amikacyn, cefoxitim and ciprofloxacyn, and M. chelonae to cefoxitim and amikacyn. Monotherapy is not recommended under any circumstances. Differential diagnosis of cutaneous disease due to atypical mycobacteria must be made with all those clinical entities manifested by nodules, abscesses, ulcers or draining sinuses, such as tuberculosis, sporotrichosis, nocardiosis and botriomicosis. Atypical mycobacteria are among the agents which can produce skin nodules and abscesses of lymphangitic spread. In pulmonary disease, the main differential diagnosis is tuberculosis. When there are abscesses at the centre of granulomas, aiypical mycobacteria etiology must be suspected. These microorganisms are widely distributed in nature. The main source of transmission of these atypical mycobacteria to humans is via water. Strict supervision for their application to man, use of disposable syringes and needles, adequate disinfection of reusable material and equipment with proven mycobactericidals, ¡.e., 2% alkaline glutaraldehyde, and minimal biosecurity standards prevent diseases caused by atypical mycobacteria.