Indian Journal of Experimental Biology Vol.49, July 2011, pp. 547-551 Distinct synergistic action of piperacillin and methylglyoxal against Pseudomonas aeruginosa Sayanti Mukherjee a , Shaswati Chaki a , Sukhen Das b , Saswati Sen c , Samir Kr. Dutta c & Sujata G. Dastidar a* a Department of Microbiology, Herbicure Healthcare Bio-Herbal Research Foundation, 7&8 Metro Garden City, D.H. Road, Pailan, Kolkata 700 104, India b Department of Physics, Jadavpur University, Kolkata 700 032, India c Division of Drug Development/Diagnostics and Biotechnology, Indian Institute of Chemical Biology, (IICB) CSIR, Kolkata 700 032, India Received 12 October 2010, revised 28 March 2011 The dicarbonyl compound methylglyoxal is a natural constituent of Manuka honey produced from Manuka flowers in New Zealand. It is known to possess both anticancer and antibacterial activity. Such observations prompted to investigate the ability of methylglyoxal as a potent drug against multidrug resistant Pseudomonas aeruginosa. A total of 12 test P. aeruginosa strains isolated from various hospitals were tested for their resistances against many antibiotics, most of which are applied in the treatment of P. aeruginosa infections. Results revealed that the strains were resistant to many drugs at high levels, only piperacillin, carbenicillin, amikacin and ciprofloxacin showed resistances at comparatively lower levels. Following multiple experimentations it was observed that methylglyoxal was also antimicrobic against all the strains at comparable levels. Distinct and statistically significant synergism was observed between methylglyoxal and piperacillin by disc diffusion tests when compared with their individual effects. The fractional inhibitory concentration index of this combination evaluated by checkerboard analysis, was 0.5, which confirmed synergism between the pair. Synergism was also noted when methylglyoxal was combined with carbenicillin and amikacin. Keywords: Antimicrobial action, Methylglyoxal, Piperacillin, Pseudomonas aeruginosa, Synergism The growing problem of multi-drug resistant (MDR) 1 opportunistic human pathogen Pseudomonas aeruginosa have been studied and discussed extensively. The quest is on to combat this deadly pathogen which at any given chance of immune disorder in a host can be fatal. There have been a lot of investigations on the discovery and application of newer antibiotics alone and in combination, but the multiple virulence factors present in P. aeruginosa 2,3 continuously try and develop ways and means to overcome their application. Continuous high rate of mutation coupled with other factors have resulted in occurrence of MDR strains. Therefore, search for different compounds, other than antibiotics which can be effective against MDR P. aeruginosa may open up a new pathway in its history of pathogenesis and treatment. Methylglyoxal (Mg) which is an aldehyde form of P. aeruginosa glycolysis end product of pyruvic acid can be obtained as a natural component of Manuka Honey 4 . It is a special type of honey obtained from Manuka flowers which generally grow in New Zealand and are found to be highly antimicrobic in nature. Though antibacterial activity of methylglyoxal has been reported 5 , more extensive research is needed. Piperacillin (Pp) which is one of the recent drugs of choice against potential Gram negative pathogens is an antibiotic that can be administered alone in pseudomonal infections 6 . But with the extensive progress of MDR strains, the activity and efficacy of piperacillin is decreasing rapidly 7 . Hence the present study has been designed to estimate the potency of methylglyoxal alone and in combination with piperacillin against recent human isolates along with a standard strain of P. aeruginosa for evaluation of a possible synergistic combination. Materials and Methods Bacteria—A total of 12 strains of pathogenic P. aeruginosa were taken for this study. Of these ATCC 27853 was received from American Type —————— * Correspondent author Telephone: 919836029744 Fax: 9133-22874042 E-mail: jumicrobiol@yahoo.co.in