Comparative antimicrobial activity of crude and partially purified Weissella cibaria NM1 postbiotics against Klebsiella pneumoniae ATCC13382.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is of clinical concern due to its resilience against antibiotics. Among potential alternatives for treatment, postbiotics from lactic acid bacteria (LAB) incite interest due to having strong antimicrobial activities whilst being generally recognised as safe. However, insights into their components and interactions remain limited. Weissella cibaria NM1 produces the proteinaceous postbiotic NM1 that inhibits K. pneumoniae ATCC13382. This study aims to compare the anti-K. pneumoniae activities of crude postbiotic NM1 and its partially-purified protein fractions via minimum inhibitory concentration (MIC) and time-kill assays. The purification of postbiotic NM1 revealed two cationic and six anionic fractions with yields of 0.03-1.08% and purification folds of 0.02-1.47 times. Crude postbiotic NM1 had the lowest MIC at 15.63 mg/mL, as compared to the MICs of its partially purified NM1 fractions at 125-250 mg/mL. The partially purified fractions were bacteriostatic, achieving reductions of 0.07-1.30 log10 CFU/mL within 1-8 h, but the crude postbiotic NM1 was bactericidal, achieving complete inhibition by 8 h of incubation. The purification of postbiotic NM1 highlights its richly diverse antimicrobial makeup that provide the robust activity retained in its crude form, showing potential for practical applications even before extensive purification.