The mycobacterial embCAB operon encodes arabinosyl transferases, putative targets of the antimycobacterial agent ethambutol (EMB). Mutations in embB lead to resistance to EMB in Mycobacterium tuberculosis. The basis for natural, intrinsic resistance to EMB in nontuberculous mycobacteria (NTM) is not known; neither is the practical implication of resistance to EMB in the absence of embB mutations in M. tuberculosis well understood. The conserved embB resistance-determining region (ERDR) of a collection of 13 strains of NTM and 12 EMB-resistant strains of M. tuberculosis was investigated. Genotypes were correlated with drug susceptibility phenotypes. High-level natural resistance to EMB (MIC, . or =64 microg/ml) was associated with a variant amino acid motif in the ERDR of M. abscessus, M. chelonae, and M. leprae. Transfer of the M. abscessus emb allele to M. smegmatis resulted in a 500-fold increase in the MICs. In M. tuberculosis, embB mutations were associated with MICs of > or =20 microg/ml while resistance not associated with an ERDR mutation generally resulted in MICs of < or =10 microg/ml. These data further support the notion that the emb region determines intrinsic and acquired resistance to EMB and might help in the reassessment of the current recommendations for the screening and treatment of infections with EMB-resistant M. tuberculosis and NTM.

We prospectively studied 485 episodes of bacteremia in neutropenic patients with cancer. Viridans streptococci caused a total of 88 episodes (18%). T

Sixty-four of 85 (75.3%) smear-negative respiratory ( n = 78) and nonrespiratory ( n = 7) samples with positive cultures of Mycobacterium tuberculosis complex (MTC) were detected by the GeneXpert system using the Xpert MTB/RIF assay (GX). In addition, GX found rpoB mutations in all six of the rifampin-resistant strains detected. The test was negative in 20 culture-negative and 20 nontuberculous culture-positive samples (100% specificity). GX offers high potential for the diagnosis of tuberculosis due to its capacity for direct detection of MTC, its rapidity, and its simplicity.

The 198-amino-acid in-frame insertion in the gyrA gene of Mycobacterium xenopi is the smallest known naturally occurring active protein splicing element (intein). Comparison with other mycobacterial gyrA inteins suggests that the M. xenopi intein underwent a complex series of events including (i) removal of 222 amino acids that encompass most of the central intein domain, and (ii) addition of a linker of unrelated residues. This naturally occurring genetic rearrangement is a representative characteristic of the taxon. The deletion process removes the conserved motifs involved in homing endonuclease activity. The linker insertion represents a structural requirement, as its mutation resulted in failure to splice. The M. xenopi GyrA intein thus provides a paradigm for a minimal protein splicing element.

DESPITE advances in antibiotic therapy, pneumonia remains a major cause of morbidity and mortality.^1-3 In recent years, a change in the patient population with pneumonia, which includes an increasing number of patients immunosuppressed by human immunodeficiency virus infection, transplantation, immunosuppressive drugs, and cancer, has been noted.⁴ However, investigators have excluded such patients from most prospective studies, and the American Thoracic Society has provided guidelines that exclude immunosuppressed patients.^5,6 Therefore, there is a need for studies dealing with pneumonia in the different groups of immunosuppressed patients.