Antimicrobial effect of dimethyl sulfoxide and N, N-Dimethylformamide on Mycobacterium abscessus: Implications for antimicrobial susceptibility testing

Background: The emergence of antimicrobial resistance globally has initiated the discovery of novel antibiotics and other antimicrobial substances. Many of these novel compounds may be found in phytochemicals, where these novel compounds are extremely difficult to redissolve for antimicrobial susceptibility testing, following extraction. The aim of this study was to examine the potential antimicrobial effects of the common solvents, dimethyl sulfoxide (DMSO) and N, N-dimethylformamide (DMF), which are commonly employed as solvents of novel antimicrobial substances, with the nontuberculous Mycobacterium and Mycobacterium abscessus. Methods: M. abscessus clinical isolates (n = 17 isolates) were examined for the antimicrobial effects of DMSO and DMF. McFarland 0.5 standards of each isolate were prepared individually on Columbia Blood agar onto which DMSO and DMF were added (10 μl) in the range neat (undiluted) – 10,000-fold (10−4) dilution and incubated. Zones of inhibition were recorded in mm. Results: DMSO and DMF had an inhibitory effect on M. abscessus (n = 17 clinical isolates). This inhibitory effect was avoided by diluting DMSO 10-fold and DMF 10,000-fold. Conclusion: Such data are important when employing these common solvents with molecules which are difficult to dissolve into solution, including conventional antibiotics, as well as novel antimicrobial agents, particularly in antimicrobial susceptibility studies. Investigators should therefore be aware of this inhibition and avoid working with these solvents at high concentration to avoid bacterial growth inhibition. The use of appropriate experimental controls is highly recommended in such circumstances to avoid the reporting of false-positive antimicrobial effects.