Bacteria can tolerate high levels of antibiotics in salt

In the natural environment, bacteria can experience salt stress, for instance, due to spontaneous water evaporation from bio-aerosols. We monitored the proliferation of the bacteria, Mycobacterium smegmatis, over multiple generations in a microfluidic chip. Surprisingly, in elevated salt concentrations, the bacteria could tolerate high concentrations of antibiotics, indicating salt-induced drug resistance. 

See our publication: DOI: 10.1039/D5LC00713E (Paper) Lab Chip, 2025, Advance Article

Salt stress also led to slower growth, shorter cell length, and reduced division asymmetry. Dye-based efflux assays showed minimal early activation of known efflux genes, but upregulation of ribosomal biosynthesis and stress adaptation. 

In general, these findings demonstrate how abiotic stress promotes phenotypic drug tolerance and reshapes antibiotic susceptibility prior to developing genetic resistance, thus providing valuable insights into managing the global threat of antibiotic resistance.

The video shows Mycobacterium smegmatis treated with streptomycin + different concentrations of salt (NaCl). Although growth is slow, bacteria can survive in high salt.