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.
Highlights
Solvents are essential in several industries where they are used to dissolve solutes and as reaction media for low water soluble substrates and/or products
The aim of this study was the following: (i) to determine the tolerance of M. vaccae to ethanol, glycerol, methyl tert-butyl ether (MTBE) and toluene and to assess the modifications occurring at the level of the fatty acid composition of the phospholipids of the cellular membrane during cell adaptation to the listed solvents; (ii) to adapt M. vaccae cells to the presence of organic solvents and assess if solvent-adapted cells present higher tolerance toward anti-mycobacterial drugs when compared with non-adapted cells
M. vaccae may be found in the environment, and human contact with this species may be facilitated during outdoor activities and through agricultural products, and by water distribution systems (Falkinham, 2009)
Summary
Solvents are essential in several industries where they are used to dissolve solutes and as reaction media for low water soluble substrates and/or products. Bacteria exposed to toxic organic solvents developed an array of mechanisms to thrive, including extrusion of solvents through efflux pumps (Isken and de Bont, 1996; Ramos et al, 1998; de Carvalho et al, 2014), enzymatic modification of the toxic compound (Tay et al, 1998; de Carvalho and da Fonseca, 2005; Tyagi et al, 2011), morphological changes (de Carvalho et al, 2004a), vesicle formation (Ramos et al, 2002; Baumgarten et al, 2012), accumulation of storage lipids (Cortes and de Carvalho, 2015), adjustments in the fatty acid composition of cells (Heipieper and de Bont, 1994; de Carvalho et al, 2005a; Nielsen et al, 2005; Unell et al, 2007; de Carvalho, 2012), modification of phospholipid headgroups (Ramos et al, 2002), phospholipid content and biosynthesis rate (Pinkart and White, 1997). These mechanisms have been extensively reviewed for Gram-negative bacteria but studies regarding tolerance mechanisms in Grampositive bacteria have been gaining interest
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