Insights into the antibacterial activity of Limosilactobacillus fermentum curd isolate against gram-positive and gram-negative pathogenic bacteria

Abstract

It is widely known that lactic acid bacteria (LAB), commonly found in fermented products like curd, extends health benefits and antibacterial properties, particularly in traditional Chinese medicine (TCM). In spite of the growing demand for sweet curd contained in earthen pots in our region, no research has specifically explored its unique properties. This study aims to address this gap by examining the probiotic characteristics, antibacterial activity and consumer appeal of sweet curd in earthen pots. A sweet curd sample containing in an earthen pot was microbiologically cultured to isolate LAB applying conventional methods and 16S rRNA gene sequencing. The strain thus isolated was identified to be Limosilactobacillus fermentum 406B, showed broad-spectrum antibacterial activity against gram-positive: Staphylococcus aureus, Bacillus cereus, Streptococcus pneumoniae and Listeria monocytogenes and gram-negative: Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Proteus vulgaris bacterial pathogens. Antimicrobial property and minimum inhibitory concentration (MIC) were assessed by agar well diffusion and broth dilution method, respectively. Initial tests based on colony morphology, gram staining and biochemical assays confirmed it as a Lactobacillus species, with sequencing confirming its identity as Limosilactobacillus fermentum 406B. The strain demonstrated excellent physiological tolerance to NaCl, bile, low pH and varying temperatures, confirming its suitability as a probiotic. Additionally, safety tests showed that it was non-pathogenic, as it tested negative for gelatinase and DNase production and displayed an acceptable antibiotic susceptibility profile. With a cumulative probiotic potential (CPP) of 100 %, L. fermentum 406B holds significant promise as a probiotic strain. These results underscore the strain’s potential not just in TCM but also as a prospective biotherapeutic agent, considering its extensive antibacterial activity and robust safety profile.