Can mycobacterial katG genetic changes in isoniazid-resistant tuberculosis influence human disease features?

BACKGROUND: Isoniazid-resistant (INHr) Mycobacterium tuberculosis isolates often have katG mutations, and katG is a virulence factor in animal models. It is unclear if katG mutations or other mutations influence the characteristics of human disease. OBJECTIVE: To determine if the presence of INHr-conferring mutations were associated with distinct clinical features of tuberculosis (TB). METHODS: In a retrospective case-control study, INHr-conferring mutations were determined by DNA sequencing. We examined associations between clinical characteristics in patients with INHr M. tuberculosis (stratified by groups of relevant INHr-conferring mutations, including katG-S315T and inhA-C(-)15T mutations) and pan-susceptible (PS) isolates. RESULTS: Twenty-nine INHr TB cases and 50 PS controls were evaluated. Disease characteristics were not statistically different between INHr and PS cases. However, patients infected with non-katG mutants were associated with a higher rate of sputum culture conversion at 1 month after adjustment for relevant covariates (adjusted OR [aOR] 4.4, 95%CI 1.1-23.6, P = 0.04). Patients infected with katG mutants were associated with a higher rate of unilateral disease (aOR 4.7, 95%CI 1.0-34.3, P = 0.05). CONCLUSIONS: Most INHr TB cases with non-katG mutations have disease associated with faster response to treatment, and most cases with katG mutants have localized lung involvement.

Analysis of mutations in the pbp genes of penicillin-non-susceptible pneumococci from Turkey.

Sequence analysis of the pbp genes from 20 Streptococcus pneumoniae isolates from Turkey (eight with high-level penicillin-resistance, nine with low-level penicillin-resistance, and three that were penicillin-susceptible) was performed and phylogenetic trees were constructed. Most isolates clustered together within a single branch that was distinct from sequences deposited previously in GenBank, which suggests that these isolates have probably evolved following new recombination events. The most prominent active-site mutations, which have also been associated previously with resistance, were T371A in PBP1a, E481G followed by T451A in PBP2b, and T338A in PBP2x. All isolates also possessed a (570)SVES/TK(574) block in the PBP2b sequence, instead of the QLQPT sequence of R6, which is fairly uncommon in GenBank sequences. This is the first study to analyse alterations in the pbp sequences of pneumococci isolated in Turkey.

Molecular genetic analysis of nucleotide polymorphisms associated with ethambutol resistance in human isolates of Mycobacterium tuberculosis.

Ethambutol (EMB) is a central component of drug regimens used worldwide for the treatment of tuberculosis. To gain insight into the molecular genetic basis of EMB resistance, approximately 2 Mb of five chromosomal regions with 12 genes in 75 epidemiologically unassociated EMB-resistant and 33 EMB-susceptible Mycobacterium tuberculosis strains isolated from human patients were sequenced. Seventy-six percent of EMB-resistant organisms had an amino acid replacement or other molecular change not found in EMB-susceptible strains. Thirty-eight (51%) EMB-resistant isolates had a resistance-associated mutation in only 1 of the 12 genes sequenced. Nineteen EMB-resistant isolates had resistance-associated nucleotide changes that conferred amino acid replacements or upstream potential regulatory region mutations in two or more genes. Most isolates (68%) with resistance-associated mutations in a single gene had nucleotide changes in embB, a gene encoding an arabinosyltransferase involved in cell wall biosynthesis. The majority of these mutations resulted in amino acid replacements at position 306 or 406 of EmbB. Resistance-associated mutations were also identified in several genes recently shown to be upregulated in response to exposure of M. tuberculosis to EMB in vitro, including genes in the iniA operon. Approximately one-fourth of the organisms studied lacked mutations inferred to participate in EMB resistance, a result indicating that one or more genes that mediate resistance to this drug remain to be discovered. Taken together, the results indicate that there are multiple molecular pathways to the EMB resistance phenotype.

Identification of esg, a genetic locus involved in cell-cell signaling during Myxococcus xanthus development.

JD258, a Tn5 insertion mutant of Myxococcus xanthus, was shown to have major defects in three development-associated properties: expression of the developmentally regulated tps gene, spore formation, and production of multicellular fruiting bodies. The defects in tps gene expression and sporulation could be substantially corrected, at the phenotypic level, by mixing JD258 with wild-type cells (extracellular complementation). By this criterion, JD258 appeared to be a new member of a group of conditional developmental mutants that were previously characterized and placed in four extracellular complementation groups (A to D) based on the ability of mutants in one group to stimulate development in mutants belonging to a different group (D. C. Hagen, A. P. Bretscher, and D. Kaiser, Dev. Biol. 64:284-296, 1978). Mutants from groups A, B, C, and D all displayed extracellular complementation activity when mixed with JD258. These results, and other aspects of the phenotype of JD258, indicate that this mutant defines a fifth extracellular complementation group, group E. The M. xanthus esg locus identified by the Tn5 insertion in JD258 was cloned in Escherichia coli and used for further genetic analysis of the locus. These studies indicated that the esg locus resides within a 2.5-kb region of the M. xanthus chromosome and that the locus contains at least two genetic complementation groups. Our results are consistent with a model in which the esg locus controls the production of a previously unrecognized extracellular signal that must be transmitted between cells for the completion of M. xanthus development.