SUMMARY Molecular typing has revolutionized epidemiological studies of infectious diseases, including those of a mycobacterial etiology. With the advent of fingerprinting techniques, many traditional concepts regarding transmission, infectivity, or pathogenicity of mycobacterial bacilli have been revisited, and their conventional interpretations have been challenged. Since the mid-1990s, when the first typing methods were introduced, a plethora of other modalities have been proposed. So-called molecular epidemiology has become an essential subdiscipline of modern mycobacteriology. It serves as a resource for understanding the key issues in the epidemiology of tuberculosis and other mycobacterial diseases. Among these issues are disclosing sources of infection, quantifying recent transmission, identifying transmission links, discerning reinfection from relapse, tracking the geographic distribution and clonal expansion of specific strains, and exploring the genetic mechanisms underlying specific phenotypic traits, including virulence, organ tropism, transmissibility, or drug resistance. Since genotyping continues to unravel the biology of mycobacteria, it offers enormous promise in the fight against and prevention of the diseases caused by these pathogens. In this review, molecular typing methods for Mycobacterium tuberculosis and nontuberculous mycobacteria elaborated over the last 2 decades are summarized. The relevance of these methods to the epidemiological investigation, diagnosis, evolution, and control of mycobacterial diseases is discussed.

Background: Rifampin is a first line antituberculosis drug active against bacilli in logarithmic and stationary phase, which interferes with RNA synthesis by binding to bacterial RNA polymerase. Tubercle bacilli achieve resistance to rifampin by accumulation of mutations in a short-81 bp region of therpoBgene. Among many mutations identified in therpoB gene, few were verified by molecular genetic methods as responsible for resistance to rifampin (RMP).Results: In this study eight different mutations identified in an 81 bp section of a "hot spot" region of therpoB gene of RMP resistantMycobacterium tuberculosisclinical strains were evaluated in respect to drug resistance. It was found that: mutations in positions 526 (H/D), 516 (D/V) and 531 (S/L) result in high level resistance to rifampin; mutations in positions 516 (D/Y), 515 (M/I), 510 (Q/H) or a double mutation in codons 512 (S/I) and 516 (D/G) relate to low level of resistance. GenerpoB carrying mutations in codon 513 (Q/L) introduced into anM. tuberculosislaboratory strain did not cause resistance to rifampin, however the same gene introduced into two different clinical strains did, with the level of resistance depending on the host strain.Conclusion: Mutations in an 81 bp "hot spot" region of therpoBofM. tuberculosislead to different levels of resistance to rifampin. Some mutations in this "hot spot" region ofrpoBrequire a specific genetic background for the host strain to develop resistance to rifampin. Therefore, the identification of such mutations in a clinicalM. tuberculosisstrain is not enough to classify the given strain as resistant to rifampin.

Resistance ofMycobacterium tuberculosisto rifampin (RMP), mediated by mutations in therpoBgene coding for the beta-subunit of RNA polymerase, poses a serious threat to the efficacy of clinical management and, thus, control programs for tuberculosis (TB). The contribution of many individualrpoBmutations to the development and level of RMP resistance remains elusive.

Tuberculosis (TB) is a severe infectious disease with high mortality and morbidity. The emergence of drug-resistant TB has increased the challenge to eliminate this disease. Isoniazid (INH) remains the key and effective component in the therapeutic regimen recommended by World Health Organization (WHO). A series of isoniazid-carborane derivatives containing 1,2-dicarba-closo-dodecaborane, 1,7-dicarba-closo-dodecaborane, 1,12-dicarba-closo-dodecaborane, or 7,8-dicarba-nido-undecaborate anion were synthesized for the first time. The compounds were tested in vitro against the Mycobacterium tuberculosis (Mtb) H37Rv strain and its mutant (ΔkatG) defective in the synthesis of catalase-peroxidase (KatG). N′-((7,8-dicarba-nido-undecaboranyl)methylidene)isonicotinohydrazide (16) showed the highest activity against the wild-type Mtb strain. All hybrids could inhibit the growth of the ΔkatG mutant in lower concentrations than INH. N′-([(1,12-dicarba-closo-dodecaboran-1yl)ethyl)isonicotinohydrazide (25) exhibited more than 60-fold increase in activity against Mtb ΔkatG as compared to INH. This compound was also found to be noncytotoxic up to a concentration four times higher than the minimum inhibitory concentration 99% (MIC₉₉) value.

Nitrogen is an essential component of biological molecules and an indispensable microelement required for the growth of cells. Nitrogen metabolism of Mycobacterium smegmatis is regulated by a number of transcription factors, with the glnR gene product playing a major role. Under nitrogen-depletion conditions, GlnR controls the expression of many genes involved in nitrogen assimilation, including the msmeg_0432 gene encoding NnaR, the homologue of a nitrite/nitrate transport regulator from Streptomyces coelicolor. In the present study, the role of NnaR in the nitrogen metabolism of M. smegmatis was evaluated. The ∆glnR and ∆nnaR mutant strains were generated and cultured under nitrogen-depletion conditions. Total RNA profiling was used to investigate the potential role of NnaR in the GlnR regulon under nitrogen-depletion and in nitrogen-rich media. We found that disruption of MSMEG_0432 affected the expression of genes involved in nitrite/nitrate uptake, and its removal rendered mycobacteria unable to assimilate nitrogen from those sources, leading to cell death. RNA-Seq results were validated using quantitative real-time polymerase chain reaction (qRT-PCR) and electrophoretic mobility shift assays (EMSAs). The ability of mutants to grow on various nitrogen sources was evaluated using the BIOLOG Phenotype screening platform and confirmed on minimal Sauton’s medium containing various sources of nitrogen. The ∆glnR mutant was not able to convert nitrates to nitrites. Interestingly, NnaR required active GlnR to prevent nitrogen starvation, and both proteins cooperated in the regulation of gene expression associated with nitrate/nitrite assimilation. The ∆nnaR mutant was able to convert nitrates to nitrites, but it could not assimilate the products of this conversion. Importantly, NnaR was the key regulator of the expression of the truncated haemoglobin trHbN, which is required to improve the survival of bacteria under nitrosative stress.

Due to a variety of physicochemical properties of the sewage sludge the selection of proper methods for its stabilization is difficult. In this work, the effect of ozone treatment on physico-chemical and microbiological parameters of sludge was investigated. Ozonation was carried out using a counter-current bed reactor, which ensures optimal mass transfer and the contact time of ozone with excessive sediment. The ozonation process was carried out for 15, 30, 45 and 60 min at an ozone concentration of 90–110 ppm. As a result of the ozone treatment it was possible to reduce the number of colony forming units. Also the potential for dewatering of the sludge improved while the total solids of the sludge did not change. The values of COD and BOD₅ increased with time of the process.