Lack of association of novel mutation Asp397Gly in aftB gene with ethambutol resistance in clinical isolates of Mycobacterium tuberculosis.

To discover additional genotypic indicators for ethambutol (EMB) resistant M. tuberculosis, we studied polymorphisms in arabinofuranosyl transferase encoding genes aftA (Rv3792), aftB (Rv3805) and aftC (Rv2673) in 38 EMB resistant and 34 EMB susceptible isolates from India and a repository established by the World Health Organization (WHO) Special Programme for Research and Training in Tropical Disease (TDR) by DNA sequencing. The results were correlated with the minimum inhibitory concentration (MIC) of EMB and mutations in embB (Rv3795). The most common non-synonymous polymorphism identified in aftB was Asp397Gly in 12/38 (31.6%) EMB resistant and 3/34 (8.8%) EMB susceptible isolates. Interestingly, 10/12 (83.3%) EMB resistant isolates with aftB Asp397Gly mutation also carried embB306, embB402 or embB497 mutations. Association of Asp397Gly polymorphism with EMB resistance was statistically significant (p 0.0216). However, overexpression of the mutant aftB in M. tuberculosis H37Rv did not exhibit any change in the MIC. Whole genome sequencing of a panel of Indian isolates and SNP cluster grouping (SCG) of TDR strains revealed an association between aftB mutation Asp397Gly and Beijing genotype or SCG2, a cluster group representing the Beijing genotype. To conclude, though aftBAsp397Gly mutation is not associated with EMB resistance, this mutation may be a phylogenetic marker for the Beijing clade.

Polymorphisms in Rv3806c (ubiA) and the upstream region of embA in relation to ethambutol resistance in clinical isolates of Mycobacterium tuberculosis from North India.

Mutations at embB306 are the most prevalent polymorphisms associated with ethambutol (EMB) resistance, responsible for 40-60% of EMB resistant clinical cases of tuberculosis (TB). The present study analyzed additional mutations associated with EMB resistance in the embB, embC, embA and Rv3806c (ubiA) genes in 29 EMB resistant and 29 EMB susceptible clinical isolates of M. tuberculosis selected from 360 patients with TB. The entire ubiA gene, mutational hotspot regions of embB, embC, and upstream region of embA were screened for polymorphisms by DNA sequencing and the results correlated with minimum inhibitory concentrations (MIC) of EMB. The most common polymorphism identified in ubiA was at codon 149 (GAA to GAC), occurring in 5/29 (17.2%) resistant isolates and 7/29 (24%) susceptible isolates. Mutations in embB were most common at codon 306 (ATG to ATC/GTG), occurring only in EMB resistant isolates (20/29; 69%). Mutations in the upstream region of embA at -8, -11, -12 and -60 codons also occurred in EMB resistant strains (8/29; 27.5%) of which 6/8 (75%) were observed in isolates with EMB MIC ≥16 µg/ml. Though no polymorphisms associated with EMB resistance were identified in ubiA, polymorphisms upstream to embA may contribute to high level EMB resistance.

A snapshot of the predominant single nucleotide polymorphism cluster groups of Mycobacterium tuberculosis clinical isolates in Delhi, India.

Several attempts have been made to associate phylogenetic differences among Mycobacterium tuberculosis strains to variations in the clinical outcome of the disease and to drug resistance. We genotyped 139 clinical isolates of M. tuberculosis obtained from patients of pulmonary tuberculosis in North Delhi region. The isolates were analyzed using nine Single nucleotide polymorphism (SNP) markers, spoligotyping and MIRU-VNTRs; and the results were correlated with their drug susceptibility profile. Results of SNP cluster group (SCG) analysis (available for 138 isolates) showed that the most predominant cluster was SCG 3a, observed in 58.7% (81/138) of the isolates with 44.4% (36/81) of these being drug susceptible, while 16% (13/81) were multidrug resistant (MDR). Of the ancestral cluster SCG 1 observed in 19.5% (27/138) of the isolates, 14.8% (4/27) were MDR while 44.4% (12/27) were drug susceptible. SCG 2 formed 5.79% (8/138) of the isolates and 50% (4/8) of these were multidrug resistant (MDR). Spoligotyping subdivided the strains into 45 shared types (n = 125) and 14 orphan strains. The orphan strains were mostly associated with SCG 3a or SCG 1, reflecting the principal SCGs found in the Indian population. SCG 1 and SCG 2 genotypes were concordant with the East African Indian (EAI) and Beijing families respectively. Central Asian (CAS) clade and its sublineages were predominantly associated with SCG 3a. No consistent association was seen between the SCGs and Harlem, T or X clades. The 15 loci MIRU-VNTR typing revealed 123/136 isolates to be unclustered, while 13 isolates were present in 6 clusters of 2-3 isolates each. However, correlating the cluster analysis with patient details did not suggest any evidence of recent transmission. In conclusion, though our study revealed the preponderance of SCG 1 and 3a in the M. tuberculosis population circulating in the region, the diversity of strains highlights the changes occurring within lineages and reemphasizes the importance of cluster investigations in extended studies.

Bisphosphonate therapy for skeletal malignancies and metastases: impact on jaw bones and prosthodontic concerns.

Healthy jawbones ensure better tooth anchorage and the ability to masticate and maintain metabolism. This is achieved by a delicate balance between bone formation and resorption in response to functional demands. An imbalance in the expression of receptor activator of nuclear factor kappa-B (RANK) ligand (RANKL) and osteoprotegerin (OPG) or osteoclastogenesis inhibitory factor (OCIF) is believed to be the underlying mechanism of osteolysis in metastases, multiple myelomas, and cancer therapy-induced bone loss in patients. Considered mainly as bone-specific agents to treat postmenopausal osteoporosis, bisphosphonates, in combination with certain chemotherapeutic agents have proved to be effective in prevention of tumor formation and metastatic osteolysis in bone tissue. Osteonecrosis of the jaws associated with them has, however, been of grave concern to the prosthodontist, as it predisposes patients to a bone-deficient basal seat for dental prostheses. This manuscript reviews available information over the past 13 years on possible mechanisms of bone loss, bisphosphonate-induced osteonecrosis of jaw bones, and prosthodontic concerns.