Enzyme immunoassay on whole Nocardia asteroides cells for human nocardiosis

Immunodiagnosis of nocardiosis

A specific immunodominant 54-kDa antigen was purified from a culture filtrate of Nocardia asteroides by immunoaffinity chromatography. The chromatography column was prepared with immunoglobulin G obtained from sera from patients with lepromatous leprosy. Unbound solutes consisted of specific, partially purified N. asteroides antigens, primarily a 54-kDa band, accompanied by two others of 31 and 62 kDa. The Western blot (immunoblot) technique was applied to detecting the immunologic response to nocardiae in the serum of nocardiosis patients. Each of the serum samples from immunosuppressed or immunocompetent patients infected with N. asteroides reacted with the 54-kDa band, and two reacted with the 31- and 62-kDa bands. There was no reaction to either the 54- or the 31-kDa antigen with all serum samples obtained from patients with tuberculosis, except for one, with all serum samples obtained from patients with leprosy, or with all sera obtained from healthy controls. The partially purified 54-kDa antigen, specific for N. asteroides, was used as the immunogen to generate monoclonal antibodies (mAbs) and two mAbs were selected. As determined by Western blot, both mAbs reacted with the 54-kDa band. Using indirect immunofluorescence or enzyme immunoassay with whole N. asteroides micro-organisms, the mAbs did not react with N. asteroides cells. No cross-reactivity with mycobacterial antigens, either culture-filtrate antigens or tuberculin, was exhibited with any of the two mAbs. These mAbs are candidates to be used for the development of a sensitive and specific diagnostic test for nocardiosis.

Serum antibodies to pathogenic actinomycetes in the normal human population

Sera of persons without known actinomycotic infection (n = 153) were tested for antibodies reacting with antigenic preparations of different Actinomyces spp. and Nocardia spp. By using an enzyme immunoassay, 16% of all of the sera analyzed reacted significantly with antigens of A. viscosus and 2% those of with A. naeslundii. The antigens detected by these antibodies were of low molecular mass (14-32 kDa) and showed a uniform reaction pattern in the immunoblot analysis. Multiple bands coccurred with a difference of approximately 2 kDa in size suggesting the presence of repetitive units. Analogous antibodies were not observed with A. israelii serovar 1 and serovar 2 antigens, which were only insignificantly bound by the sera. The antibodies demonstrated were most probably acquired during episodes of periodontal disease or gingivitis in which A. viscosus is etiologically involved. Antibodies against nocardial antigens were not demonstrated in significant proportions by enzyme immunoassay and immunoblot analysis.

Characterization of Nocardia, Rhodococcus and Gordona species by in vitro susceptibility testing

Representative strains of Gordona, Nocardia and Rhodococcus were tested against 26 antimicrobial agents using the disc diffusion method. A distinct susceptibility profile was noted for most species. Nocardia asteroides, N. brasiliensis, N. otitidiscaviarum, N. transvalensis and N. vaccinii were rarely susceptible to the antibiotics tested; N. brevicatena and N. farcinica varied in their susceptibility depending on the strain tested. Only the antibiotic amikacin was active against all nocardiae. In contrast, the Gordona and Rhodococcus strains showed considerable susceptibility, in particular to the beta-lactam antibiotics. Amoxicillin + clavulanic acid and gentamicin were active against all of the gordonae and rhodococci. The differences in susceptibility patterns may prove useful in characterizing the genera Gordona, Nocardia and Rhodococcus and in separating species within these taxa.