Anti-enterococcal and anti-oxidative potential of a thermophilic cyanobacterium, Leptolyngbya sp. HNBGU 003

Enterococci, the opportunistic pathogens, pose several serious and life-threatening infections such as urinary tract infections, sepsis, and endocarditis. The situation is worsening due to the development of drug resistance in these pathogens against several antibiotics. The addition of anti-enterococcal compounds with antioxidant activity in fermented and packaged food may help prevent the transmission of food-borne enterococcal infections. Scientists are in continuous search of such compounds from various sources. Hence, the present study has tested the diethyl ether extracts of thermophilic cyanobacteria, selected based on a previous study, against the multidrug-resistant and -sensitive strains of Enterococcus faecium. Out of the eleven tested extracts, 72% have shown anti-enterococcal activity against both strains. Among the extracts with anti-enterococcal activity, the diethyl ether extract of Leptolyngbya sp. (DEEL-3) inhibited the growth of VRE in a dose-dependent manner with a minimum inhibitory concentration of 2.0 mg mL^-1. The DEEL-3 has also shown its antioxidant potential in terms of DPPH scavenging with an IC₅₀ of 3.16 mg mL^-1. The organism was named Leptolyngbya sp. HNBGU 003 based on 16SrRNA sequence homology analysis and morphological features. Further, the GC-MS analysis of the DEEL-3 has revealed the predominance of two phenolic compounds, phenol, 2,4-bis(1,1-dimethylethyl)-, phosphite (3:1) and tris(2,4-di-tert-butylphenyl) phosphate, in it. Thus, the anti-enterococcal and antioxidant activity of DEEL-3 may be attributed to these phenolics, which may be isolated and developed as food additives.