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

Background: Tuberculosis (TB) caused by (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 3,6,9 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 3,6,9 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 3, 6, and 9 toxin genes, the 3, 6, and 9 antitoxin genes, and expression of the MazF9 protein were detected in the different MTB strains, H37RvΔ3,6,9 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. 3,6 mRNA-expression levels were relatively reduced in the drug-sensitive and drug-resistant strains compared to H37Rv. Conversely, 3,9 expression was increased in drug-sensitive strains compared to drug-resistant strains. Furthermore, compared with the H37Rv strain, 3,6 expression was increased in drug-resistant strains, 9 expression was increased in drug-sensitive strains, and 9 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, H37RvΔ3,6,9-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 H37RvΔF3,6,9 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. 3,6,9 TASs contribute to MTB viability under stress conditions.