Significance: It is not known whether natural immunity to TB exists or whether antibodies play an important role in immunity against infection by Mycobacterium tuberculosis (Mtb), the causative agent of TB. Here, we identify that a significant minority of healthcare workers who are exposed to high doses of Mtb make protective antibodies against infection as measured in both mouse infection and in vitro models. Some of these individuals had no prior evidence of latent TB infection, suggesting that they may represent a subset of “restrictors” who can control infection by Mtb. These results have important implications in the rational development of both protective and therapeutic vaccines against TB.

Extensively drug-resistant tuberculosis (XDR-TB) is a deadly form of TB that can be incurable due to its extreme drug resistance. In this study, we aimed to explore the in vitro susceptibility to bedaquiline (BDQ), delamanid (DMD), linezolid (LZD), clofazimine (CLO), moxifloxacin (MFX), and gatifloxacin (GAT) of 90 XDR-TB strains isolated from patients in China. We also describe the genetic characteristics of XDR-TB isolates with acquired drug resistance. Resistance to MFX, GAT, LZD, CLO, DMD, and BDQ was found in 82 (91.1%), 76 (84.4%), 5 (5.6%), 5 (5.6%), 4 (4.4%), and 3 (3.3%) isolates among the XDR-TB strains, respectively. The most frequent mutations conferring fluoroquinolone resistance occurred in codon 94 of the gyrA gene (57.8%), and the strains with these mutations (69.2%) were associated with high-level MFX resistance compared to strains with mutations in codon 90 (25.0%) ( P < 0.01). All 5 CLO-resistant isolates exhibited ≥4-fold upward shifts in the BDQ MIC, which were attributed to mutations of codons 53 (60.0%) and 157 (20.0%) in the Rv0678 gene. Additionally, mutation in codon 318 of the fbiC gene was identified as the sole mutation related to DMD resistance. In conclusion, our data demonstrate that the XDR-TB strains exhibit a strikingly high proportion of resistance to the current anti-TB drugs, whereas BDQ, DMD, LZD, and CLO exhibit excellent in vitro activity against XDR-TB in the National Clinical Center on TB of China. The extensive cross-resistance between OFX and later-generation fluoroquinolones indicates that MFX and GAT may have difficulty in producing the desired effect for XDR-TB patients.

Oxazolidinones are efficacious in treating mycobacterial infections, including tuberculosis (TB) caused by drug-resistant Mycobacterium tuberculosis . In this study, we compared the in vitro activities and MIC distributions of delpazolid, a novel oxazolidinone, and linezolid against multidrug-resistant TB (MDR-TB) and extensively drug-resistant TB (XDR-TB) in China. Additionally, genetic mutations in 23S rRNA, rplC , and rplD genes were analyzed to reveal potential mechanisms underlying the observed oxazolidinone resistance. A total of 240 M. tuberculosis isolates were included in this study, including 120 MDR-TB isolates and 120 XDR-TB isolates. Overall, linezolid and delpazolid MIC ₉₀ values for M. tuberculosis isolates were 0.25 mg/liter and 0.5 mg/liter, respectively. Based on visual inspection, we tentatively set epidemiological cutoff (ECOFF) values for MIC determinations for linezolid and delpazolid at 1.0 mg/liter and 2.0 mg/liter, respectively. Although no significant difference in resistance rates was observed between linezolid and delpazolid among XDR-TB isolates ( P > 0.05), statistical analysis revealed a significantly greater proportion of linezolid-resistant isolates than delpazolid-resistant isolates within the MDR-TB group ( P = 0.036). Seven (53.85%) of 13 linezolid-resistant isolates were found to harbor mutations within the three target genes. Additionally, 1 isolate exhibited an amino acid substitution (Arg126His) within the protein encoded by rplD that contributed to high-level resistance to linezolid (MIC of >16 mg/liter), compared to a delpazolid MIC of 0.25. In conclusion, in vitro susceptibility testing revealed that delpazolid antibacterial activity was comparable to that of linezolid. A novel mutation within rplD that endowed M. tuberculosis with linezolid, but not delpazolid, resistance was identified.

Tuberculosis (TB) recurrence can result from either relapse of an original infection or exogenous reinfection with a new strain of Mycobacterium tuberculosis (MTB). The aim of this study was to assess the roles of relapse and reinfection among recurrent TB cases characterized by a high prevalence rate of drug-resistant TB within a hospital setting. After 58 paired recurrent TB cases were genotyped to distinguish relapse from reinfection, 37 (63.8%) were demonstrated to be relapse cases, while the remaining 21 were classified as reinfection cases. Statistical analysis revealed that male gender was a risk factor for TB reinfection, odds ratios and 95% confidence interval (OR [95% CI]: 4.188[1.012–17.392], P = 0.049). Of MTB isolates obtained from the 37 relapse cases, 11 exhibited conversion from susceptible to resistance to at least one antibiotic, with the most frequent emergence of drug resistance observed to be levofloxacin. For reinfection cases, reemergence of rifampicin-resistant isolates harboring double gene mutations, of codon 531 of rpoB and codon 306 of embB, were observed. In conclusion, our data demonstrate that relapse is a major mechanism leading to TB recurrence in Beijing Chest Hospital, a national hospital specialized in TB treatment. Moreover, male patients are at higher risk for reinfection. The extremely high rate of multidrug-resistant tuberculosis (MDR-TB) among reinfection cases reflects more successful transmission of MDR-TB strains versus non-resistant strains overall.

Mycobacterium tuberculosis can acquire resistance to rifampin (RIF) through mutations in the rpoB gene. This is usually accompanied by a fitness cost, which, however, can be mitigated by secondary mutations in the rpoA or rpoC gene. This study aimed to identify rpoA and rpoC mutations in clinical M. tuberculosis isolates in northern China in order to clarify their role in the transmission of drug-resistant tuberculosis (TB). The study collection included 332 RIF-resistant and 178 RIF-susceptible isolates. The majority of isolates belonged to the Beijing genotype (95.3%, 486/510 isolates), and no mutation was found in rpoA or rpoC of the non-Beijing genotype strains. Among the Beijing genotype strains, 27.8% (89/320) of RIF-resistant isolates harbored nonsynonymous mutations in the rpoA ( n = 6) or rpoC ( n = 83) gene. The proportion of rpoC mutations was significantly higher in new cases ( P = 0.023) and in strains with the rpoB S531L mutation ( P < 0.001). In addition, multidrug-resistant (MDR) strains with rpoC mutations were significantly associated with 24-locus mycobacterial interspersed repetitive-unit–variable-number tandem-repeat clustering ( P = 0.016). In summary, we believe that these findings indirectly suggest an epistatic interaction of particular mutations related to RIF resistance and strain fitness and, consequently, the role of such mutations in the spread of MDR M. tuberculosis strains.