Combination effect of isothiocyanates and antibiotics against bacterial uropathogens

Background Isothiocyanates (ITC) are natural sulfur compounds derived from a variety of plants, e.g. nasturtium and horseradish, which possess impressive antimicrobial activity. We investigated the effects of a natural mixture of ITC in combination with different antibiotics against common bacterial uropathogens.

Materials/methods Tests were performed using the agar/disc diffusion method. A mixture of three ITC was used containing benzyl-, allyl- and phenylethyl-ITC in combination with seven different antibiotics (AB), i.e. ampicillin, ampicillin/sulbactam, ciprofloxacin, cotrimoxazole, gentamicin, nitrofurantoin, and fosfomycin. Test organisms were ten clinical isolates of A. baumannii (n = 2), E. coli (n = 6), E. cloacae (n = 1), K. pneumoniae (n = 1), in addition to E. coli ATCC 25922 (control).

Results After exposure to the antimicrobial combination (ITC+AB), there was individual response: Interestingly, the combinations ITC + fosfomycin and ITC + imipenem showed an impressive increase in the antimicrobial susceptibilities among all clinical isolates tested. Seven clinical isolates showed a significant increase in the susceptibility for ITC + gentamicin. ITC + ciprofloxacin produced increased susceptibilities in 2 of 10 clinical isolates. In particular, ITC + nitrofurantoin improved antimicrobial susceptibilities in E. coli. There was little or no effect for ITC + aminopenicillin or ITC + cotrimoxazole.

Conclusions ITC possess intrinsic antimicrobial activity; in combination with antibiotics, however, they may lead to an extension of the antibiotic spectrum, even against antibiotic resistant strains. Therefore, combinations of ITC + AB may represent an innovative approach for effectively treating bacterial infections, e.g. of the urinary tract.

Publication History

Article published online:
07 October 2020