Viability, biofilm formation, and MazEF expression in drug-sensitive and drug-resistant Mycobacterium tuberculosis strains circulating in Xinjiang, China

Background Tuberculosis (TB) caused by Mycobacterium tuberculosis (MTB) is one of the most common chronic infectious amphixenotic diseases worldwide. Prevention and control of TB are greatly difficult, due to the increase in drug-resistant TB, particularly multidrug-resistant TB. We speculated that there were some differences between drug-sensitive and drug-resistant MTB strains and that mazEF3,6,9 toxin-antitoxin systems (TASs) were involved in MTB viability. This study aimed to investigate differences in viability, biofilm formation, and MazEF expression between drug-sensitive and drug-resistant MTB strains circulating in Xinjiang, China, and whether mazEF3,6,9 TASs contribute to MTB viability under stress conditions. Materials and methods Growth profiles and biofilm-formation abilities of drug-sensitive, drug-resistant MTB strains and the control strain H37Rv were monitored. Using molecular biology experiments, the mRNA expression of the mazF3, 6, and 9 toxin genes, the mazE3, 6, and 9 antitoxin genes, and expression of the MazF9 protein were detected in the different MTB strains, H37RvΔmazEF3,6,9 mutants from the H37Rv parent strain were generated, and mutant viability was tested. Results Ex vivo culture analyses demonstrated that drug-resistant MTB strains exhibit higher survival rates than drug-sensitive strains and the control strain H37Rv. However, there was no statistical difference in biofilm-formation ability in the drug-sensitive, drug-resistant, and H37Rv strains. mazE3,6 mRNA-expression levels were relatively reduced in the drug-sensitive and drug-resistant strains compared to H37Rv. Conversely, mazE3,9 expression was increased in drug-sensitive strains compared to drug-resistant strains. Furthermore, compared with the H37Rv strain, mazF3,6 expression was increased in drug-resistant strains, mazF9 expression was increased in drug-sensitive strains, and mazF9 exhibited reduced expression in drug-resistant strains compared with drug-sensitive strains. Protein expression of mazF9 was increased in drug-sensitive and drug-resistant strains compared to H37Rv, while drug-resistant strains exhibited reduced mazF9 expression compared to drug-sensitive strains. Compared to H37Rv, H37RvΔmazEF3,6,9-deletion mutants grew more slowly under both stress conditions, and their ability to survive in host macrophages was also weaker. Furthermore, the host macrophage-apoptosis rate was higher after infection with any of the H37RvΔmazEF3,6,9 mutants than with the H37Rv strain. Conclusion The increased viability of MTB drug-resistant strains compared with drug-sensitive strains is likely to be related to differential MazEF mRNA and protein expression. mazEF3,6,9 TASs contribute to MTB viability under stress conditions.