Characterization of lactic acid bacterium Pediococcus pentosaceus 4I1 from fresh water fish Zacco koreanus and its antibacterial mode of action

The present study aimed to characterize a lactic acid bacterium Pediococcus pentosaceus 4I1, isolated from the intestine of fresh water fish sample Zacco koreanus. Biochemical analysis using the API 50 CHL kit and molecular characterization of 4I1 revealed its identity as a lactic acid bacterium Pediococcus pentosaceus 4I1. Further, cell free supernatant (CFS) of P. pentosaceus 4I1 exhibited significant (p<0.05) antibacterial effect as diameters of inhibition zones (16.5–20.4 mm) against the tested foodborne pathogenic bacteria with minimum inhibitory (MIC) and minimum bactericidal (MBC) concentration values found in the range of 250-500 and 500-1,000 µg/mL, respectively. Further, to confirm the efficacy of 4I1 on membrane permeability against foodborne pathogens, antibacterial mode of action of CFS of P. pentosaceus 4I1 against two selected bacteria Staphylococcus aureus KCTC-1621 (gram-positive) and Escherichia coli O157:H7 (gram-negative) was determined by measuring cell viable count, release of 260-nm absorbing materials, leakage of potassium ions and measurement of relative electrical conductivity of the bacterial cells treated at MIC concentration. The CFS of P. pentosaceus 4I1 revealed its mode of action on membrane integrity as confirmed by reduction in viable cell count, increased release of potassium ions (900 and 800 mM/L), loss of 260-nm absorbing materials (3.99 and 3.77 OD), and increase in relative electrical conductivity (9.9 and 9.7%) against the tested bacteria S. aureus KCTC-1621 and E. coli O157:H7, respectively. The above findings hypothesize that P. pentosaceus 4I1 compromised its mode of action on membrane integrity, suggesting its enormous potential in food and pharma industries.