We examined the molecular mechanisms of resistance to kanamycin and viomycin in Mycobacterium smegmatis. All of the M. smegmatis strains with high-level kanamycin resistance had a nucleotide substitution from A to G at position 1389 of the 16S rRNA gene (rrs). This position is equivalent to position 1408 of Escherichia coli, and mutation at this position is known to cause aminoglycoside resistance. Mutations from G to A or G to T at position 1473 of the M. smegmatis rrs gene were found in viomycin-resistant mutants which had been designated vicB mutants in our earlier studies. Using the M. smegmatis conjugation system, we confirmed that these mutations indeed contributed to kanamycin and viomycin resistance, and kanamycin susceptibility was dominant over resistance in a heterogenomic strain. Additional experiments showed that three of four Mycobacterium tuberculosis strains with high-level kanamycin resistance had a mutation from A to G at position 1400, which was equivalent to position 1389 of M. smegmatis.

No abstract

Using 39 clinical isolates of Mycobacterium strains with a broad range of susceptibility to rifampicin, we examined the relationship between the degree of resistance to rifampicin and mutational sites of the rpoB gene. All rifampicin-resistant strains had missense mutations. Twenty strains (95%) had a mutation in the cluster I region, which has also been reported in Escherichia coli [Jin and Gross (1988) J. Mol. Biol. 202, 45-58], and the remaining one strain had a mutation at codon 381 [Ala-->Val] in the N-terminal region, which has not been reported in E. coli. Among 18 rifampicin-susceptible strains, two had a mutation in the cluster I region and the other three strains had a mutation in the cluster III region. The mutations at codons 513 (5%), 526 (33%) or 531 (43%) in the cluster I region led to high level resistance to rifampicin (50 micrograms ml-1 < or = MIC). The mutations at the other sites, in the cluster III region (codons 679 or 687) and even in the cluster I region (codon 514, 521, or 533), showed low level (MIC = 12.5 micrograms ml-1) or no (MIC < 0.39 microgram ml-1) resistance to rifampicin. These results suggest that mutations in the rpoB gene are, mostly, but not necessarily, associated with rifampicin resistance of M. tuberculosis, and the sites of mutations on the rpoB gene will affect the level of resistance to rifampicin.

It has been shown that Legionella pneumophila proliferates intracellularly in more than ten species of protozoa, but the fate of the bacteria in Tetrahymena thermophila has not been reported. We investigated the multiplication of L. pneumophila Philadelphia-1 strain in micronucleated T. thermophila, and the effects of temperature and numbers of the bacteria ingested by the protozoa after in vitro feeding were studied. T. thermophila preyed actively upon the bacteria. After being ingested, the fate of the bacteria was affected by both temperature and the number of bacteria ingested. When the number of ingested bacteria was 30 per protozoon, the bacteria proliferated intracellularly at 35 degrees C. The bacteria, however, could not proliferate at 28 degrees C or 32 degrees C though they survived in the protozoa. When the ingested bacteria was 10 per protozoon, the bacteria were killed in the protozoa at all of the temperatures tested. Electron microscopic examination revealed that the protozoa ingesting the bacteria remarkably swelled and that protozoan food vacuoles which contained L. pneumophila were studded with ribosomes.

To characterize the clinical features of patients with idiopathic pulmonary fibrosis (IPF) having organizing pneumonia (OP), we retrospectively reviewed the clinical charts, chest X-rays, CT scans, and transbronchial lung biopsy (TBLB) specimens of patients with IPF. Patients with IPF and OP had a subacute onset of symptoms (within 2 months) (87.5%), leukocytosis ( > 10,000/ mm³) (62.5%), and a strong C-reactive protein (CRP) reaction ( > 3+) (75%). Some of these features were distinctly different from those of IPF patients without OP (subacute onset of symptoms 0%, leukocytosis 0%, strong CRP reaction 16.7%). In the patients with IPF with OP, A-aDO₂ and semiquantitative scores of chest X-ray abnormalities improved significantly after prednisolone treatment. Those abnormalities improved only slightly in the patients with IPF without OP. Diffusing capacity remained decreased and abnormal interstitial infiltration persisted, even after prednisolone treatment in the patients with IPF with or without OP. Clinical features of IPF patients with OP differed from those of patients with IPF without OP. IPF patients with OP showed good clinical response to corticosteroid therapy. These findings warrant further study of the presence of OP in TBLB specimens in predicting corticosteroid responsiveness and prognosis of patients with IPF.