Mycobacterial Response to Organic Solvents and Possible Implications on Cross-Resistance With Antimicrobial Agents

Abstract

Mycobacterium vaccae, a bacterium found in soil, has been receiving attention as adjuvant to antituberculosis treatment, vaccines and immunotherapies and even as antidepressant. This bacterium is also able to degrade several pollutants, including aromatic compounds. The increasing presence of organic solvents in the environment may lead to M. vaccae adapted populations. A possible relationship between solvent tolerance and decreased susceptibility to other types of chemicals, including antibiotics, may pose a problem during opportunistic infections. The present study thus aimed at assessing if solvent adapted cells presented higher tolerance to antibiotics and efflux pump inhibitors (EPIs). M. vaccae cells were able to thrive and grow in the presence of up 20% (v/v) glycerol, 5% (v/v) ethanol, 1% (v/v) methyl tert-butyl ether (MTBE) and 0.1% (v/v) toluene. During adaptation to increasing concentration of ethanol and MTBE, the cells changed their fatty acid profile, zeta potential and morphology. Adapted cells acquired an improved tolerance toward the EPIs thioridazine and omeprazole, but became more susceptible to the antibiotics levofloxacin and teicoplanin when compared with non-adapted cells.

Mycobacterium vaccae Adaptation to Disinfectants and Hand Sanitisers, and Evaluation of Cross-Tolerance with Antimicrobials

“…To evaluate the effect of disinfectants commonly used in health care facilities on M. vaccae cells, the disinfectants were initially added at sub-lethal concentrations to cultures in mid-exponential phase. This classical approach, to study the effect of toxic compounds, allows de novo synthesis of fatty acids, if necessary, for the response of the cells at the membrane composition level [ 19 , 31 ]. After the addition of the disinfectant, the cells were monitored for 8 h. For comparison, the fatty acid (FA) composition of the exposed M. vaccae cells is presented after 6 h, which is higher than one duplication time in the presence of all tested disinfectants ( Figure 1 , Supplementary Table S1 ).…”

“…Nevertheless, a model containing a lipid bilayer as outer membrane and an inner membrane, rich in diacyl phosphatidylinositol dimannosides, which also contribute to the generalized drug resistance of mycobacteria, has been proposed [ 48 ]. We have also shown that changes in the lipid composition of the cell envelop of M. vaccae contribute to the adaptation of this bacterium to organic solvents [ 19 ].…”

“…However, little is known from increased tolerance resulting from phenotypic adaptations of the cells exposed to disinfectants and antiseptics. Modifications to, e.g., the FA composition of the cellular membrane of bacterial cells, may hamper the entrance of other compounds, such as antibiotics and disinfectants, in the cell and prevent their action, or cells may convert the compound into non-toxic forms [ 2 , 19 ]. Such temporary, phenotypic modification may help the cells to tolerate the action of antibiotics and efflux pump inhibitors.…”

“…In a previous study, we showed that M. vaccae cells adapted to ethanol and methyl tert -butyl ether increased the tolerance towards thioridazine and omeprazole but became more susceptible to levofloxacin and teicoplanin [ 19 ]. In the present study, cells adapted to disinfectants increased their tolerance towards levofloxacin: two-fold in the case of alcohol gel adapted cells and eight-fold in the case of cells adapted to the hand disinfectant Aniosrub, when compared to non-adapted cells ( Table 1 ).…”

“…cells to organic solvents relevant for bioprocesses [ 16 , 17 , 18 ]. Additionally, we also studied M. vaccae adaptation to organic solvents and showed that the adapted cells increased tolerance toward the efflux pump inhibitors (EPIs) thioridazine and omeprazole, but were more susceptible to the antibiotics levofloxacin and teicoplanin when compared to non-adapted cells [ 19 ]. Major responses involved alterations at the lipid composition of the cellular membranes which were accompanied by changes in the zeta potential of the surface of the cells.…”