*3.2. Antimicrobial and Antioxidant Potential of Isolates*

In this study, all seven isolates showed antibacterial activity against at least one test bacterium. All isolates inhibited MRSA strains significantly (MRSA ATCC 33591, MRSA ATCC NR-46071, and MRSA ATCC 46171), whereas showed less inhibition potential against Gram-negative bacteria *Salmonella typhi* (ATCC 25241) and *Escherichia coli* (ATCC 11775). The isolates namely S1A, SS5, SCA35, and SCA 11 inhibited *Fusarium moniliforme* (MTCC 6576) to a maximum extent (Figure 6). The minimum inhibition concentration (MIC) ranges from 15.62 to 125 μg/mL for MRSA strains, 125–500 μg/mL for Gram-negative bacteria, and 62.5–250 μg/mL for fungi (Table 4). Numerous studies have reported antimicrobial activity of actinobacterial species. Sengupta et al. [28] reported

potential antimicrobial activity of three isolates against *Pseudomonas aueroginosa*, *Enterobacter aueroginosa*, *Salmonella typhi*, *Salmonella typhimurium*, *Escherichia coli*, *Bacillus subtilis*, and *Vibrio cholera*. Satheeja and Jebakumar [29] reported isolation of *Streptomcyes* species from a mangrove ecosystem for antibacterial activity against clinical isolates of MRSA, methicillin-susceptible *Staphylococcus aureus* (MSSA), and *Salmonella typhi*. Vu et al. [30] reported antimicrobial activity of *Streptomyces cavourensis* YBQ59 against methicillin-resistant *Staphylococcus aureus* ATCC 33591 and methicillin-resistant *Staphylococcus epidermidis* ATCC 358984. Dashti et al. [31] reported the co-cultivation of *Actinokineospora* sp.EG49 and *Nocardiopsis* sp.RV163 and metabolites produced were tested for antimicrobial activity against the range of pathogens. The bioactive metabolite from *Streptomyces cyaneofuscatus* M-169 showed significant inhibition of Gram-positive bacteria with MIC value of 0.03 μg/mL [32]. It has been shown that actinobacterial isolates from Western Ghats exhibit antimicrobial activity. The *Streptomyces* species from Agumbe [33], *Streptomyces* sp. RAMPP-065 from Kudremukh [34], and *Streptomyces* sp. GOS1 isolated from Western Ghats of Agumbe, Karnataka [35] exhibited remarkable antimicrobial activity. In earlier studies, *Streptomyces* species isolated from Kodachadri were found to possess antifungal activity [33]. Each extract was evaluated for scavenging activity against DPPH and ABTS radicals for antioxidant activity. Crude extract of strain SCA11 showed potent scavenging activity against DPPH radicals with IC50 (μg/mL) 30.91 ± 0.25, whereas SCA13 showed remarkable scavenging activity against ABTS radicals with IC50 (μg/mL) 37.91 ± 0.17. Trolox as a standard showed significant activity with IC50 (μg/mL) 11.07 ± 0.06 and 9.87 ± 0.01 against DPPH and ABTS radicals, respectively (Table 5). Similar studies were carried out for the detection of compounds with antioxidant activity from *Streptomyces* spp., dihydroherbimycin A [36], 5-(2,4-dimethylbenzyl)pyrrolidin-2-one [37]. Ser et al. [38] reported antioxidant activity of pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro extracted from *Streptomyces mangrovisoli*, a novel *Streptomyces* species isolated from a mangrove forest in Malaysia. Narendhran et al. [39] successfully reported antioxidant potential of phenol, 2,4-bis(1,1-dimethylethyl) in *Streptomyces cavouresis* KUV39 isolated from vermicompost samples. Tian et al. [40] reported antioxidant, antifungal, and antibacterial activity of *p*-Terphenyls isolated from halophilic actinobacteria *Nocardiopsis gilva* YIM 90087. Current findings indicated the bioactive potential of actinobacterial isolates from Western Ghats region of Karnataka. The isolates were found to possess significant antimicrobial activity against Gram-positive MRSA bacteria, Gram-negative bacteria, and fungal pathogens. They also exhibited potent scavenging activity against DPPH and ABTS radicals suggesting their antioxidant potential. It is anticipated that findings of the study will be useful in the discovery of novel species of actinobacteria for a potential source of bioactive compounds from underexplored environments.

**Figure 4.** Phylogenetic analysis of isolate *Nocardioides* sp. strain SCA13. Neighbor-joining phylogenetic tree showing evolutionary relationship of selected isolate based on 16S r-RNA sequence alignments. Bootstrap values at the nodes indicate collated values based on 1000 resampleddatasets. Bar indicates 0.001 substitutions per nucleotide position.

**Figure 5.** Neighbor-joining phylogenetic tree showing evolutionary relationship between isolates S1A, SS4, SS5, SS6, and SCA35 based on 16S r-RNA sequence alignments. Bootstrap values at the nodes indicate collated values based on 1000 resampled datasets. Bar indicates 0.005 substitutions per nucleotide position.

**Figure 6.** Antimicrobial activity of actinobacterial isolates against (**A**) MRSA ATCC NR 46071, MRSA ATCC NR 46171, and MRSA ATCC 33591 (**B**) *Escherichia coli* ATCC 11775 and *Salmonella typhi* ATCC 25241, (**C**) *Fusarium moniliforme* MTCC 6576.

**Table 4.** Minimum inhibitory concentration (MIC in μg/mL) of actinobacterial isolates against pathogenic test organisms.


**Table 5.** Comparison of IC50 (μg/mL) of crude extracts and trolox for DPPH and ABTS radical scavenging activity.

