F. Rubab, M.F. Chaudhary, N.M. Butt
Keywords: zinc oxide nanoparticles, antibacterial effect, DZI, drinking water
Summary:In the area of water purification, nanotechnology offers the possibility of an efficient removal of pollutants and germs (Dhermendra K. Tiwari et al., 2008). Zinc oxide nanoparticles are known to be one of the multifunctional inorganic nanoparticles with effective antibacterial activity (Sangeetha et al., 2012). Application of ZnO nanoparticles is also beneficial because of their low toxicity to human and antibacterial properties besides that zinc is essentially required by humans as part of their mineral nutrition. This study aims to determine the antibacterial efficacy of zinc oxide nanoparticles against various Gram negative bacteria isolated from local sources of drinking water. We have been able to isolate and identify Escherichia coli, Serratia marcescens, Enterobacter cloacae, Aeromonas hydrophila, Cronobacter sakazakii, Pseudomonas aeruginosa and klebsiella pneumoniae. Various microbiological tests were performed using various concentrations and working volumes of zinc oxide nanoparticles with average size of 35 nm and a few results have already been reported (TechConnect Briefs 2015, Vol. 1: pp 344-348) showing the antibacterial efficacy of ZnO NPs against E. coli, S. marcescens, E. cloacae, A. hydrophila and C. sakazakii. Current results showed the antibacterial activity of different concentrations (0, 100, 200, 300 & 500 mg/ml) of zinc oxide nanoparticles against P. aeruginosa and k. pneumoniae. Highest zone of inhibition i.e. 29 mm was observed at 500 mg/ml against p. aeruginosa while k. pneumoniae showed a 20 mm zone of inhibition at 500 mg/ml as shown in Fig.1. When different volumes (0, 10, 20, 30, 40, 50, 60 µl) of ZnO NPs (Concentration 500 mg/ml) were tested the highest zone of inhibition i.e. 24 mm was observed at 60 µl against P. aeruginosa while k. pneumoniae showed 20 mm zone of inhibition as shown in Fig. 2. Antibiotic susceptibility of different antibiotics was also tested against same bacteria and compared with ZnO NPs. Both P. aeruginosa and k. pneumoniae showed highest susceptibility against Ciprofloxacin (CIP) showing 34 & 33 mm zone of inhibition while lowest susceptibility was observed against Erythromycin (ERYC) as shown in Fig 3. Synergistic effect of ZnO nanoparticles with antibiotics was also studied against Escherichia coli, Serratia marcescens, Enterobacter cloacae, Aeromonas hydrophila and Cronobacter sakazakii. Antibiotic efficacy of Erythromycin (ERYC) and Trimethoprim Sulfamethaxozole (SXT) was enhanced by the addition of ZnO NPs (5 µl) of 500 mg/ml. Erythromycin showed only DZI of 7 mm against E. cloacae but the same antibiotic along with ZnO NPs showed zone of inhibition of 12 mm against E. cloacae as shown in Fig. 4, a marked increase due synergistic effect.