Pathogenic Nocardia isolated from clinical specimens including those of AIDS patients in Thailand

Abstract

Forty strains of nocardioform microorganisms were isolated as clinical specimens including several from AIDS patients in Thailand. Among them, 37 strains were found to belong to the genus Nocardia. Our identification studies revealed that most of the strains (25 strains) belong to the N. asteroides group, i.e., N. asteroides sensu stricto and N. farcinica. Three strains were identified as N. otitidiscaviarum and two strains N. brasiliensis. In addition, 7 strains of rare pathogenic N. transvalensis were also isolated.

PIP: Nocardia is an aerobic gram-positive and partly acid-fast bacterium that belongs to the pathogenic actinomycetes. Nocardia can cause both systemic and cutaneous diseases. Cutaneous nocardiosis is thought to be induced by various predisposing factors, the most common of which include corticosteroid therapy, immunosuppressive therapy, and hematological malignancy. In recent years cases of infection have been increasing coupled with the increased use of immunosuppressive agents and the number of AIDS patients. Characterization studies of pathogenic Nocardia isolated clinically in Thailand from 1990 to 1994 were reported. 40 strains of nocardioform microorganisms (Nocardia like actinomycetes with meso-DAP, arabinose, galactose, and mycolic acid) were isolated as clinical specimens including several from AIDS patients. All 40 strains were isolated from clinical specimens at seven hospitals in Bangkok using Sabouraud dextrose agar medium or Ogawa medium. The analysis of mycolic acid profiles on thin-layer chromatography (TLC) plate showed that one strain had the same Rf values as that of Mycobacterium sp. and the remaining 39 strains had similar Rf values to those of Nocardia, Rhodococcus, and Gordona spp. Studies on their menaquinone composition showed that among 39 isolates, 37 strains had MK-8H4 (cycl.) as predominant menaquinone. 2 strains had MK-8(H2) as a predominant menaquinone and both were identified as Rhodococcus spp. 25 strains were found to belong to the N. asteroides group and were further divided into respective species, i.e., 12 strains of N. asteroides in a strict sense and 13 strains of N. farcinica on the basis of Na-citrate utilization, susceptibility to antimicrobial and antitumor agent (tobramycin and 5-fluorouracil), and ability to grow at 45 degrees Celsius. Three strains of N. otitidiscaviarum and two strains of N. brasiliensis were also identified and the remaining seven strains were eventually identified as N. transvalensis. Results of the drug susceptibility pattern test of Nocardia isolates correlated well with those obtained by the traditional identification system. Among 37 cases, there were 10 HIV seropositive and 2 seronegative patients, and the remaining cases were unknown. Further epidemiological studies may be needed to determine a possible association between AIDS and nocardiosis.