Antibacterial and Antibiofilm Activities of Nonpolar Extracts of Allium stipitatum Regel. against Multidrug Resistant Bacteria.

Arunkumar Karunanidhi,Sridevi Chigurupati,Mallikarjuna Rao Pichika,Ehsanollah Ghaznavi-Rad,Rukman Awang Hamat,Leslie Than Thian Lung,Fazlin Mohd Fauzi,Alex Van Belkum,Vasanthakumari Neela

doi:10.1155/2018/9845075

Abstract

The present study assessed the in vitro antibacterial and antibiofilm potential of hexane (ASHE) and dichloromethane (ASDE) extracts of Allium stipitatum (Persian shallot) against planktonic cells and biofilm structures of clinically significant antibiotic resistant pathogens, with a special emphasis on methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and emerging pathogens, Acinetobacter baumannii and Stenotrophomonas maltophilia. Antibacterial activities were determined through disk diffusion, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), time-kill kinetics, and electron microscopy. Antibiofilm activity was assessed by XTT [2,3-bis(2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetrazolium-5-carboxanilide] reduction assay and by confocal laser scanning microscopy (CLSM). The zone of inhibition ranged from 13 to 33 mm, while the MICs and MBCs ranged from 16 to 1024 μg mL−1. Both ASHE and ASDE completely eradicated overnight cultures of the test microorganisms, including antibiotic resistant strains. Time-kill studies showed that the extracts were strongly bactericidal against planktonic cultures of S. aureus, MRSA, Acinetobacter baumannii, and S. maltophilia as early as 4 hours postinoculation (hpi). ASHE and ASDE were shown to inhibit preformed biofilms of the four biofilm phenotypes tested. Our results demonstrate the potential therapeutic application of ASHE and ASDE to inhibit the growth of gram-positive and gram-negative biofilms of clinical significance and warrant further investigation of the potential of A. stipitatum bulbs against biofilm-related drug resistance.

Highlights

Biofilms are ubiquitous in nature which can be found at the bottom of streams to extremely hot waters of hot springs
We investigated the effects of Allium stipitatum hexane extract ASDE (ASHE) and ASDE against a panel of medically important gram-positive and gram-negative bacteria followed by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) examination of the in vitro effects of ASHE and ASDE on bacterial cells at different concentrations
We further provide evidence that ASHE and ASDE can increase the susceptibility of bacterial biofilms with emphasis on methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), A. baumannii, and S. maltophilia biofilms

Summary

Introduction

Biofilms are ubiquitous in nature which can be found at the bottom of streams to extremely hot waters of hot springs. Biofilms pose a great threat due to their resistant nature to antibiotics, contamination of indwelling medical devices, forming dental plaques causing tooth decay, chronicity in wounds, and association with several illnesses from cystic fibrosis to otitis media. Biofilm forms of microbes are up to 1000-fold more resistant to antibiotics than their planktonic counterparts [1, 2]. The conditions are made more worrisome by the biofilm associated. Such diseases are most frequently caused by S. aureus, S. epidermidis, Pseudomonas aeruginosa, A. baumannii, and Enterobacteria such as Escherichia coli [3,4,5]

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