This study discussed the drug resustant TB on gene level based on WGS. The results showed that 96.1% of PZA-R isolates were MDR-TB isolates, and the rate of PZA-R was 43.8% among MDR isolates. The trends of PZA-R fluctuated in accordance with the trends of MDR, INH-R, RIF-R during 2007–2019. Further analyse suggested that PZA-R gene mutation may promote MDR, this phenomenon mainly associated with the function of PZA-R on INH-R, particularly with three associated mutations.
Among the strains collected, we found 85.7% were classified under L2, and 13.8% under L4. The Mycobacterium tuberculosis complex (MTBC) ancestor, initially identified as a pathogen, evolved into multiple lineages specialized for humans and different mammals. MTB and Mycobacterium africanum are the primary causative agents of human TB. Human-adapted MTBCs display a notable geographic structure, with certain lineages found worldwide while others show distinct geographic limitations. Globally, L2 and L4 are the most prevalent, with L2 being predominant in East Asia. L1 and L3 are primarily found in the region surrounding the Indian Ocean. Conversely, L5 and L6 are highly localized to West Africa. Additionally, L7 is predominantly present in Ethiopia[35, 36]. Africa is the continent hosting seven human-adapted MTBC lineages.
PZA, a commonly used basic drug in the treatment of MDR-TB, has been shown to reduce the treatment period of MDR-TB[37]. PZA-R hinders the prevention and treatment of MDR-TB. We found 43.8% of MDR-TB strains were resistant to PZA. The prevalence of PZA-R has been documented in various regions identified by the World Health Organization (WHO) in a 2015 study. Among cases of MDR-TB, the prevalence of PZA-R was 60.5%. Studies from Uzbekistan, Myanmar, Georgia, Sweden, Hunan Province, and Chongqing have reported that the rate of PZA-R among MDR-TB cases ranges from 57.9–73.6%[7, 38–42]. The situation with PZA-R is not promising, so we should pay more attention to PZA-R.
This study found that the number of PZA-R cases varied with the MDR, INH-R and RIF-R strains. MDR, INH-R and RIF-R strains prone to had higher risk of PZA-R. Antibiotics eliminate the susceptible population and allow resistant bacteria to dominate[43]. Dormant bacteria can remain latent in the body without being easily eliminated, increasing the likelihood of developing drug-resistant strains[44, 45]. PZA plays a crucial role in destroying dormant MTB and shortening the treatment period for MDR-TB that is sensitive to PZA [44]. When PZA-R is present, the treatment cycles for MDR-TB become longer, and patient compliance decreases, thereby accelerating the development of MDR-TB. Therefore, it is recommended to use PZA in the treatment of MDR-TB infection after confirming its sensitivity.
Mutations in the pncA gene are various, encompassing amino acid substitutions, nucleotide insertions or deletions from missense and nonsense mutations in both structural and regulatory regions [46, 47]. A study conducted in vitro saturation mutagenesis of pncA, screening for drug resistance in a comprehensive library of pncA polymorphisms, identified over 300 resistant substances that could potentially replace PZA. Additionally, PZA-R involves 171 PZase amino acids[12]. Single nucleotide polymorphisms (SNPs) are found throughout the pncA gene and its flanking regions, without specific hotspot regions. Mutations tend to concentrate in three specific regions 3–17, 61–85, and 132–142, which contain the catalytic site of the PZase[48]. Our research revealed 254 PZA-R mutations in the pncA region, indicating a wide distribution of mutations. Major mutation types were pncAc.011A > G, pncA_p.Thr76Pro, and pncA_p.Val139Leu. Therefore, understanding PZA-R in tuberculosis strains and the gene mutation spectrum in the pncA region is crucial for the prevention and management of MDR-TB.
We discovered that strains with MDR had significantly higher chances of developing three specific mutations compared to those without it. However, we did not observe any significant impact of RIF-R on gene mutations. Strains with INH-R showed a tendency towards having four types of mutations. We can conclude that the promotion of MDR by PZA primarily relies on its effect on INH-R. So, it is important to consider PZA-R and pncA gene mutation spectrum of TB for the prevention and control of MDR-TB, particularly with the three mutations and explore the mechanism. To improve prevention and management of MDR-TB, it is necessary to address barriers to implementing early diagnosis and prompt initiation of effective treatment for drug-resistant tuberculosis. Additionally, controlling risk factors and promptly treating mutated strains are crucial[49, 50].
We acknowledge several limitations of this study. The samples used in this study were only from China, which may reduce the generalizability of the findings. Expanding the sampling scope to include more diverse locations would enhance the credibility of the study. While the main findings of the research indicate that PZA-R mutations, particularly in the pncA gene region, may contribute to MDR, this effect is primarily linked to the role of PZA-R in INH-R. we could give no biochemical or transgenic substantiation of the mechanism. Thus, it is crucial to validate our discoveries with additional experimental proof in the foreseeable future. However, our study initially outlined the molecular properties of PZA-R and the correlation between PZA-R and MDR in China, offering valuable insights for the treatment of MDR-TB patients in this area plagued by high rates of MDR-TB. By considering the microbiological characteristics of the infecting bacteria and the clinical characteristics of the patient, personalized treatment can be optimized to reduce the incidence of MDR-TB. Shortening the duration of exposure to untreated MDR-TB can help in lowering the risk of MDR cases. Additionally, efforts to minimize the emergence of MDR and enhance the prevention and management of MDR-TB can lead to improved outcomes.