ORIGINAL PAPER Green synthesis of Al 2 O 3 nanoparticles and their bactericidal potential against clinical isolates of multi-drug resistant Pseudomonas aeruginosa Mohammad A. Ansari • Haris M. Khan • Mohammad A. Alzohairy • Mohammad Jalal • Syed G. Ali • Ruchita Pal • Javed Musarrat Received: 10 June 2014 / Accepted: 6 October 2014 / Published online: 11 October 2014 Ó Springer Science+Business Media Dordrecht 2014 Abstract The high prevalence of extended-spectrum b-lactamases (76.3 %) and metallo-b-lactamases (7.3 %) amongst the bacteria Pseudomonas aeruginosa is a critical problem that has set forth an enormous therapeutic challenge. The suggested role of nanoparticles as next generation anti- biotics, and inadequate information on antibacterial activity of aluminium oxide nanoparticles has led us to investigate the green synthesis of aluminium oxide nanoparticles (Al 2 O 3 NPs) using leaf extracts of lemongrass and its antibacterial activity against extended-spectrum b-lactamases and metallo- b-lactamases clinical isolates of P. aeruginosa. The synthe- sized Al 2 O 3 -NPs were characterized by scanning electron microcopy, high resolution-transmission electron micros- copy, atomic force microscopy, X-ray diffraction, Zeta potential, and differential light scattering techniques. The X-ray diffraction data revealed the average size of the spher- ical Al 2 O 3 -NPs as 34.5 nm. The hydrodynamic size in Milli Q water and Zeta potential were determined to be 254 nm and ?52.2 mV, respectively. The minimal inhibitory concentra- tion of Al 2 O 3 -NPs was found to be in the range of 1,600–3,200 lg/ml. Treatment at concentrations[2,000 lg/ml, resulted in complete growth inhibition of extended-spectrum b-lacta- mases and metallo-b-lactamases isolates. Scanning electron microcopy analysis revealed the clusters of nanoparticles attached to the bacterial cell surface, causing structural deformities in treated cells. High resolution-transmission electron microscopy analysis confirmed that nanoparticles crossed the cell membrane to become intracellular. The interaction of nanoparticles with the cell membrane eventu- ally triggered the loss of membrane integrity, most likely due to intracellular oxidative stress. The data explicitly suggested that the synthesized Al 2 O 3 -NPs can be exploited as an effec- tive bactericidal agent against extended-spectrum b-lacta- mases, non-extended-spectrum b-lactamases and metallo-b- lactamases strains of P. aeruginosa, regardless of their drug resistance patterns and mechanisms. The results elucidated the clinical significance of Al 2 O 3 -NPs in developing an effective antibacterial therapeutic regimen against the multi-drug resistant bacterial infections. The use of leaf extract of lem- ongrass for the synthesis of Al 2 O 3 -NPs appears to be cost effective, nontoxic, eco-friendly and its strong antibacterial activity against multi-drug resistant strains of P. aeruginosa offers compatibility for pharmaceutical and other biomedical applications. Keywords Green synthesis Á Lemongrass Á Al 2 O 3 -NPs Á DLS Á XRD Á Zeta potential Á HR-TEM Introduction The bacterium Pseudomonas aeruginosa has been consid- ered to be one of the most important pathogens, responsible M. A. Ansari (&) Á H. M. Khan Á M. Jalal Á S. G. Ali Nanotechnology and Antimicrobial Drug Resistance Research Laboratory, Department of Microbiology, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh 202002, U.P., India e-mail: azammicro@gmail.com M. A. Ansari Á M. A. Alzohairy Deptartment of Medical Laboratories, College of Applied Medical Science, Buraydah College, Buraydah, Saudi Arabia R. Pal Advanced Instrumentation Research Facility, Jawaharlal Nehru University, New Delhi, India J. Musarrat Department of Agricultural Microbiology, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh 202002, U.P., India 123 World J Microbiol Biotechnol (2015) 31:153–164 DOI 10.1007/s11274-014-1757-2