In vitro activity of garlic oil and four diallyl sulphides against antibiotic-resistant Pseudomonas aeruginosa and Klebsiella pneumoniae.

The in vitro antibacterial activities of garlic oil and four diallyl sulphides naturally occurring in this oil were studied against Pseudomonas aeruginosa and Klebsiella pneumoniae (total 237 clinical isolates). Garlic oil at 4 x MIC could reduce original inoculum to <or=2 log(10) in both P. aeruginosa and K. pneumoniae within 8 h. The MIC values of four diallyl sulphides against these two pathogens followed the order diallyl monosulphide > diallyl disulphide > diallyl trisulphide (DAT) > diallyl tetrasulphide (DATS) (P < 0.05). Most interactions of ceftazidime, gentamicin, imipenem and meropenem with DAT or DATS, determined according to the fractional inhibitory concentration index, showed synergic or additive effects. These results suggest that garlic oil, DAT and DATS may have potential for the prevention or treatment of nosocomial, antibiotic-resistant bacterial infections.