Antibacterial potential of cell-free supernatants from Liquorilactobacillus nagelii and Lactococcus garvieae isolated from the gastrointestinal tract of Asian green mussel (Perna viridis) against foodborne pathogenic and spoilage bacteria

Abstract

This study investigated the antibacterial activity of cell-free supernatants (CFS) from 33 lactic acid bacteria (LAB) isolated from the gastrointestinal (GI) tract of Asian green mussel (Perna viridis) against Vibrio parahaemolyticus, Staphylococcus aureus, Pseudomonas aeruginosa and Shewanella putrefaciens using the agar well diffusion method. Out of 33 isolates, three (9.1 % of the total; MG1, MG2 and MG5) exhibited strong activity against V. parahaemolyticus, with an inhibition zone in the range of 10.00–13.20 mm. The freeze-dried CFS of strains MG1, MG2 and MG5 exhibited inhibitory effects against V. parahaemolyticus, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values ranging from 4 to 16 mg/mL, 8–16 mg/mL and 8–64 mg/mL, respectively. Scanning electron microscopic images of V. parahaemolyticus cells treated with freeze-dried CFS of strains MG1, MG2 and MG5 at 4 × MIC showed cell damage as indicated by pore formation on the cell surface along with the absence of flagella, potentially caused by a synergistic effect of the major bioactive components in LAB supernatant. Freeze-dried CFS of strain MG2 at MIC (8 mg/mL) was most effective at inhibiting motility (swimming and swarming) and biofilm formation of V. parahaemolyticus, with 100 % and 98.5 % inhibition, respectively. Based on MALDI-TOF MS and the 16s rRNA gene sequence, strains MG1 and MG2 were identified as Liquorilactobacillus nagelii, while strain MG5 was identified as Lactococcus garvieae. Analysis of freeze-dried CFS from strain MG2 using LC-Q-TOF-MS revealed that 3b,6a-dihydroxy-alpha-ionol 9-[apiosyl-(1->6)-glucoside] and citric acid were the major components detected in positive and negative mode, respectively. This is the first report of strong antibacterial activity exhibited by antimicrobial agents from L. nagelii isolated from Asian green mussels. These findings suggest that antimicrobial agents derived from LAB in Asian green mussels may serve as potential biocontrol strategies for managing foodborne pathogens and spoilage bacteria.