Extracellular biosynthesis of silver nanoparticles using Bacillus subtilis and their antibacterial activity against clinical bacterial species

Nouran Hamed Assar ,Reham Ali Ibrahem,Rehab Mahmoud Abd El-Baky ,Aya Allah T Mohamed

doi:10.21608/nrmj.2021.178303

Abstract

The aims of this study were to biosynthesize silver nanoparticles (AgNPs) using Bacillus subtilis supernatant, and to evaluate their in vitro antibacterial potential against human pathogens; namely Staphylococcus aureus (Staph. aureus) and Escherichia coli (E. coli). Nanoparticles (NPs) are becoming popular in different fields of research, and are useful in combating vast number of microbial diseases. NPs may be artificially synthesized in vitro using chemical methods andor via extracellular metabolites produced by the bacterial strains. In the present study, biosynthesis of AgNPs was carried out in vitro using supernatants of B. subtilis. Biosynthesized AgNPs were characterized through several physical methods. The recorded Z-average (d. nm) was 135.0 nm; with 99.2 % of the NPs displaying a hydrodynamic distance across of 188.0 nm (SD= 117.7). The polydispersity index was 0.246 and the Zeta-potential value was - 17.2 mV, which indicates good colloidal stability. Results of the Transmission electron microscope (TEM) observation indicated that the particles were spherical in shape with an average size of 21.8- 27.5 nm. The antibacterial efficacy of the AgNPs against Methicillin resistant Staph. aureus (MRSA) and E. coli clinical isolates was evaluated in vitro using the agar well diffusion. The AgNPs demonstrated antibacterial potential against MRSA and E. coli isolates; recording 18 and 15 mm diameter of zones of inhibition, respectively. The minimum inhibitory concentration (MIC) was found to be 142 µg/ ml, while the recorded minimum bactericidal concentration (MBC) was 284 µg/ ml. The mode of action of the AgNPs was investigated using the Scanning electron microscope (SEM), which was recognized as bacterial cell lysis and elongation. Current data suggest an efficient biosynthesis of stable AgNPs by B. subtilis with remarkable antibacterial potential.

Highlights

Methicillin-resistant Staph. aureus (MRSA) is known as a serious causal agent of nosocomial infections that spreads worldwide, and has a negative impact on the patient's health resulting in huge increases in the health care costs (Luteijn et al, 2011)
About 50 isolates of Staph. aureus and 46 isolates of E. coli were recovered from patients of El Kasr El Aini Hospital, Microbiology laboratories, Egypt
As demonstrated in Fig. (2), E. coli isolates were found to be resistant to ceftazidime by 94 %, with much lower resistance to Amikacin by 24 %

Summary

Introduction

Methicillin-resistant Staph. aureus (MRSA) is known as a serious causal agent of nosocomial infections that spreads worldwide, and has a negative impact on the patient's health resulting in huge increases in the health care costs (Luteijn et al, 2011). Aureus acquires methicillin resistance by insertion of staphylococcal cassette chromosome (SCCmec) carrying the mecA gene into the microbial genome. This gene encodes for penicillin-binding protein PBP-2a, which is not inhibited by the preexisting β-lactams antibiotics (Makgotlho et al, 2009). The ability of B. subtilis strain to cause extracellular synthesis of AgNPs using 1 mM AgNO3 as a precursor solution was demonstrated. These biosynthesized AgNPs exhibited the power to counteract the clinical strains of E. coli and Staph. The objectives of this study were to investigate the ability of B. subtilis to synthesis AgNPs, and to test the antibacterial efficacy of the biosynthesized AgNPs against E. coli and MRSA

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Discussion

Conclusion