Wessel Alex J, Johnson Drew T T, Waters Christopher M
Department of Microbiology, Genetics, and Immunology, Michigan State University, East Lansing, Michigan, USA.
J Bacteriol. 2025 Apr 17;207(4):e0000425. doi: 10.1128/jb.00004-25. Epub 2025 Mar 26.
Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is a selective and differential media for the enrichment of pathogenic . We observed that an exonuclease VII () mutant of failed to grow on TCBS agar, suggesting that DNA repair mutant strains may be hampered for growth in this selective media. Examination of the selective components of TCBS revealed that bile acids were primarily responsible for the toxicity of the mutant. Suppressor mutations in DNA gyrase restored growth of the mutants on TCBS, suggesting that TCBS inhibits DNA gyrase similar to the antibiotic ciprofloxacin. To better understand what factors are important for to grow on TCBS, we generated a randomly barcoded TnSeq (RB-TnSeq) library in and have used it to uncover a range of DNA repair mutants that also fail to grow on TCBS agar. The results of this study suggest that TCBS agar causes DNA damage to similarly to the mechanism of action of fluoroquinolones, and overcoming this DNA damage is critical for growth on this selective medium.IMPORTANCETCBS is often used to diagnose cholera infection. We found that many mutant strains are attenuated for growth on TCBS agar, meaning they could remain undetected using this culture-dependent method. Hypermutator strains with defects in DNA repair pathways might be especially inhibited by TCBS. In addition, grown successively on TCBS agar develops resistance to ciprofloxacin.
硫代硫酸盐-柠檬酸盐-胆盐-蔗糖（TCBS）琼脂是一种用于富集病原菌的选择性和鉴别性培养基。我们观察到一种核酸外切酶VII（）突变体在TCBS琼脂上无法生长，这表明DNA修复突变株在这种选择性培养基中生长可能受到阻碍。对TCBS的选择性成分进行检测发现，胆汁酸是导致突变体毒性的主要原因。DNA促旋酶中的抑制突变恢复了突变体在TCBS上的生长，这表明TCBS与抗生素环丙沙星类似，会抑制DNA促旋酶。为了更好地了解在TCBS上生长的重要因素，我们构建了一个随机条形码转座子测序（RB-TnSeq）文库，并利用它发现了一系列在TCBS琼脂上也无法生长的DNA修复突变体。这项研究的结果表明，TCBS琼脂对造成的DNA损伤与氟喹诺酮类药物的作用机制类似，克服这种DNA损伤对于在这种选择性培养基上生长至关重要。重要性TCBS常用于诊断霍乱感染。我们发现许多突变株在TCBS琼脂上生长减弱，这意味着使用这种依赖培养的方法可能无法检测到它们。DNA修复途径存在缺陷的超突变株可能尤其会受到TCBS的抑制。此外，在TCBS琼脂上连续传代培养的会对环丙沙星产生耐药性。
