16S rRNA–Based Identification and Probiotic Potential of Lactobacilli Isolated from Asymptomatic COVID-19 Individuals

The gut-lung axis plays a central role in shaping immune responses during viral infections, linking intestinal microbiota composition to respiratory health. Probiotic microorganisms, particularly Lactobacillus species, are emerging as promising biotherapeutics due to their ability to inhibit pathogens and modulate host immunity. In this study, we isolated and characterized four Lactobacillus strains Lactobacillus fermentum, Lactobacillus plantarum-1, Lactobacillus plantarum-2, and Lactobacillus rhamnosus from the feces of asymptomatic COVID-19 individuals, representing a novel source of gut-derived probiotics. Identification was confirmed via 16S rRNA sequencing. Antibiotic susceptibility testing demonstrated responsiveness to clinically relevant antibiotics, while agar spot assays revealed moderate to strong inhibitory activity against key Gram-negative enteric pathogens, including Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (ATCC 25922), Shigella dysenteriae, and Vibrio cholerae O139 serogroup. These findings suggest that Lactobacilli from COVID-19 asymptomatic carriers not only exhibit robust antimicrobial properties but may also enhance gut-mediated antiviral immunity, potentially influencing respiratory defences through the gut-lung axis. Harnessing such strains offers a promising strategy for developing probiotic interventions to improve overall immunity and combat emerging viral infections. Despite in vitro focus, the isolates show encouraging probiotic potential that should be validated through in vivo studies.