Purification and characterization of an antimicrobial compound against drug-resistant MRSA and VRE produced by Streptomyces levis strain HFM-2

Abstract

Due to high resistance to medicines, multidrug-resistant (MDR) bacterial pathogens, particularly MRSA (methicillin-resistant Staphylococcus aureus) and VRE (vancomycin-resistant enterococci), are a significant public health concern for treating nosocomial infections. Researchers are developing novel compounds responding to the global rise in MDR infections. This study aimed to extract, purify, and characterize bioactive metabolites from Streptomyces levis strain HFM-2, a human gut isolate, exhibiting strong antimicrobial activity against several MDR pathogenic bacteria and fungal phytopathogens. Ethyl acetate extract of S. levis strain HFM-2 was purified using silica-gel column chromatography and reverse-phase high-performance liquid chromatography. Structure elucidation of the purified antimicrobial compound was done by performing detailed analyses including MS, IR, and NMR. The bacteriostatic activity of the compound revealed interesting values against broad-spectrum MDR pathogens. The bacterial cell destruction was recorded through SEM and fluorescence microscopy analyses. HFM-2P is displayed to be non-mutagenic and non-cytotoxic to the normal cell line. However, dose-dependent cytotoxicity was observed against the HeLa cancer cell line and exhibited antimutagenic activity against Salmonella Typhimurium strains (TA98 and TA100). This study is the first to report antiproliferative, DNA protective potential, antimutagenic properties, and antimicrobial activity of a 2,6-disubstituted chromone derivative isolated from S. levis strain HFM-2 against drug-resistant MRSA, VRE, and fungal phytopathogens. Therefore, this essential compound could be a candidate for future research in the pharmaceutical and agricultural sectors.

Keywords: Streptomyces; Antimicrobial; Antimutagenicity; Antiproliferative; DNA nicking; Drug-resistant.

Fig. 1

HPLC chromatogram of fractions from S. levis strain HFM-2: (a) partially purified fraction (b) purified fraction.

Fig. 2

Antibacterial activity of EtOAc extract and HFM-2P compound against (a) MRSA, (b) VRE, (c) E. coli, (d) S. aureus, (e) S. epidermidis, (f) K. pneumoniae sub sp. pneumoniae; (g) E. aerogenes, (h) B. subtilis, (i) C. herbarum, (j) F. oxysporum, (k) A. brassicicola, (l) C. gleosporoides E: EtOAc extract, P: Purified compound, T: Teicoplanin (30 µg/disc), M: Methicillin (10 µg/disc), V: Vancomycin (30 µg/disc).

Fig. 3

Thin layer chromatography of HFM-2P compound from S. levis strain HFM-2 (a), Bioautography of HFM-2P compound against VRE (b), MRSA (c), and F. oxysporum (d) with Rf values of 0.65.

Fig. 4

FT-IR spectrum of the purified HFM-2P compound.

Fig. 5

¹HNMR of purified HFM-2P compound.

Fig. 6

Structure of the purified compound HFM-2P as a 2,6-disubstituted chromone derivative.

Fig. 7

The SEM (scanning electron micrographs) display the effect of HFM-2P compound on MRSA, VRE, E. coli, and B. subtilis; Control (untreated cells): (a) MRSA, (d) VRE, (g) E. coli; j) B. subtilis. Cells treated with HFM-2P compound: (b) MRSA, (e) VRE, (h) E. coli, and (k) B. subtilis. Positive control: (c) MRSA treated with vancomycin, (f) VRE treated with teicoplanin, i and l) E. coli and B. subtilis treated with gentamicin.

Fig. 8

The analysis of antimutagenic activity of HFM-2P compound against S. Typhimurium TA98 strain. Different letters (a and b) on graphs represent significant differences (Tukey’s test p ≤ 0.05) among them.

Fig. 9

The analysis of antimutagenic activity of HFM-2P compound against S. Typhimurium TA100 strain. Different letters (a and b) on graphs represent significant differences (Tukey’s test p ≤ 0.05).

Fig. 10

Densitometric study of pBR322 plasmid DNA treated with HFM-2P compound in the presence of Fenton’s reagent; (Form I (supercoiled), Form II (nicked circular), and Form III (linear).