Abstract

Nitrofurantoin represents an attractive choice for empirical treatment of acute uncomplicated cystitis, and for long term prophylaxis against recurrent urinary tract infections. However, rather rare but severe adverse effects related to cumulative drug doses may occur. Bioactive compounds of plant origin combined with antibiotics can increase the sensitivity of microbial cells to such antibiotics. Garlic has antimicrobial effects against a wide range of microorganisms. The minimum inhibitory concentrations (MICs) of each of nitrofurantoin and garlic alone, and in combination were determined against 17 extended spectrum β-lactamase (ESBL) producing Escherichia coli and 24 Enterococcus spp. urinary isolates. When grown as planktonic cells, none of the E. coli isolates demonstrated resistance towards nitrofurantoin, whereas only one (4.2%) Enterococcus isolate was resistant. Garlic showed an inhibitory effect on planktonically grown ESBL producing E. coli and Enterococcus spp. with varying MICs. Each of nitrofurantoin and garlic tested alone showed an increase in the MICs for biofilm grown isolates compared to their planktonic counterparts. However, the combination of both agents led to significant decline of the MICs, whether for planktonic or biofilm forms, resulting in either synergy or addition. In conclusion, garlic enhanced the antibacterial activity of nitrofurantoin towards the tested urinary isolates.

Key words: Antimicrobial combination, biofilm, checkerboard assay, Enterococcus spp., extended spectrum β-lactamase (ESBL)-producing Escherichia coli, garlic extract, nitrofurantoin.