Enterocin LD3 from Enterococcus hirae LD3 causing efflux of intracellular ions and UV-absorbing materials in Gram-negative bacteria.

Aims: To understand the bactericidal action of enterocin LD3 against Gram-negative bacteria.

Methods And Results: Minimum inhibitory concentration (MIC) of enterocin LD3 against Micrococcus luteus MTCC 106 and Escherichia coli NCDC 135 was 80 and 112 μg ml , and minimum bactericidal concentration (MBC) was 128 and 180 μg ml , respectively. The efflux of potassium ion (K ) was 14 and 13 ppm and electrical conductivity 10·5 and 8·3 mS cm in cell-free supernatant of MIC-treated cells of M. luteus and E. coli respectively. The increased absorbance (OD ) 0·422/0·260 and 0·110/0·075 in the bacteriocin-treated cells of M. luteus MTCC 106 and E. coli, NCDC 135, respectively, suggested the release of nucleic acids and proteins. The higher infrared absorbance at 1451·82 and ~1094·30 cm further suggested its interaction with cell membrane and nucleic acids of the target bacteria. The interaction of bacteriocin with nucleic acids was also confirmed using gel retardation assay. Transmission electron microscopy of the bacteriocin-treated cells revealed disruption of cell membrane and leakage of cytoplasmic contents.

Conclusions: Enterocin LD3 demonstrates bactericidal activity against Gram-negative bacteria interacting with cell membrane and nucleic acids.

Significance And Impact Of The Study: The study discloses the possible mechanism of action of enterocin LD3 against Gram-negative bacteria which is a rare phenomenon.