Enterocin LD3 fromEnterococcus hiraeLD3 causing efflux of intracellular ions and UV‐absorbing materials in Gram‐negative bacteria

Abstract

Aims: To understand the bactericidal action of enterocin LD3 against Gramnegative 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 lg ml À1 , and minimum bactericidal concentration (MBC) was 128 and 180 lg ml À1 , respectively. The efflux of potassium ion (K + ) was 14 and 13 ppm and electrical conductivity 10Á5 and 8Á3 mS cm À1 in cell-free supernatant of MIC-treated cells of M. luteus and E. coli respectively. The increased absorbance (OD 260/280 ) 0Á422/0Á260 and 0Á110/0Á075 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 1451Á82 and~1094Á30 cm À1 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 Gramnegative 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.

Synergistically-acting Enterocin LD3 and Plantaricin LD4 Against Gram-Positive and Gram-Negative Pathogenic Bacteria

“…One of them could be involved in pore formation/disruption of the outer cell membrane allowing access of the other bacteriocin in target cells as also suggested by Chi and Holo [8]. The mechanism of action of plantaricin LD4 is not exactly known, but our recent findings suggest that enterocin LD3 causes membrane disruption and enters inside the cells interacting with nucleic acids [17].…”

“…enterica serovar Typhimurium ATCC13311 in NB medium (OD600 0.02) and incubated at 37°C for 24 h as mentioned in CLSI manual [20]. The MIC was determined as the lowest concentration of bacteriocin showing no visible bacterial growth (OD600 < 0.05) as suggested previously [17].…”

“…Untreated cells were resuspended in normal saline and used as controls. After treatment, cells were processed to visualize under transmission electron microscope as reported previously [17].…”

“…In laboratory conditions, enterocin LD3 demonstrated antimicrobial activity against different pathogens and related LAB [16]. Further, mode of action of enterocin LD3 was found to be bactericidal; involving dissipation of membrane potential and efflux of ATP, ions, proteins and nucleic acids was recorded [16,17]. Plantaricin LD4 was found to be approx.…”

Application of bacteriocins in food preservation and infectious disease treatment for humans and livestock: a review

“…133 Besides that, enterocin LD3 from Enterococcus hirae LD3 was proved to have antimicrobial effects against M. luteus MTCC 106 with MIC at 80 mg mL À1 and MBC at 128 mg mL À1 . 134 Enterocin A was also found to have inhibition activity against E. coli NCDC 135 with MIC at 112 mg mL À1 and MBC at 180 mg mL À1 . 134 In addition, enterocin AS-48 was proved to have inhibition against B. cereus ATCC 14579.…”