Antibacterial Effect of Silver Nanoparticles Synthesized Using <i>Murraya koenigii</i> (L.) against Multidrug-Resistant Pathogens

Development of multidrug resistance among pathogens has become a global problem for chemotherapy of bacterial infections. Extended-spectrum <i>β</i>-lactamase- (ES<i>β</i>L-) producing enteric bacteria and methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) are the two major groups of problematic MDR bacteria that have evolved rapidly in the recent past. In this study, the aqueous extract of <i>Murraya koenigii</i> leaves was used for synthesis of silver nanoparticles. The synthesized MK-AgNPs were characterized using UV-vis spectroscopy, FTIR, XRD, SEM, and TEM, and their antibacterial potential was evaluated on multiple ES<i>β</i>L-producing enteric bacteria and MRSA. The nanoparticles were predominantly found to be spheroidal with particle size distribution in the range of 5-20 nm. There was 60.86% silver content in MK-AgNPs. Evaluation of antibacterial activity by the disc-diffusion assay revealed that MK-AgNPs effectively inhibited the growth of test pathogens with varying sized zones of inhibition. The MICs of MK-AgNPs against both MRSA and methicillin-sensitive <i>S. aureus</i> (MSSA) strains were 32 <i>μ</i>g/ml, while for ES<i>β</i>L-producing <i>E. coli</i>, it ranged from 32 to 64 <i>μ</i>g/ml. The control strain of <i>E. coli</i> (ECS) was relatively more sensitive with an MIC of 16 <i>μ</i>g/ml. The MBCs were in accordance with the respective MICs. Analysis of growth kinetics revealed that the growth of all tested <i>S. aureus</i> strains was inhibited (∼90%) in presence of 32 <i>μ</i>g/ml of MK-AgNPs. The sensitive strain of <i>E. coli</i> (ECS) showed least resistance to MK-AgNPs with >81% inhibition at 16 <i>μ</i>g/ml. The present investigation revealed an encouraging result on <i>in vitro</i> efficacy of green synthesized MK-AgNPs and needed further <i>in vivo</i> assessment for its therapeutic efficacy against MDR bacteria.