Anti-staphylococcal activity of bacteriocins of food isolates Enterococcus hirae LD3 and Lactobacillus plantarum LD4 in pasteurized milk
Bacteriocins of Enterococcus hirae LD3 and Lactobacillus plantarum LD4 have been applied in milk for growth inhibition of Staphylococcus aureus. The enumeration of S. aureus cells in nutrient broth and milk was found log10 9.7 and 10.2 CFU/mL, respectively, whereas it was reduced with increasing concentration of bacteriocins suggesting loss of cell viability. The lethal concentration (LC50) of enterocin LD3 and plantaricin LD4 against S. aureus was 160 and 220 µg/mL, respectively. Bacteriocin-treated cells were stained red with propidium iodide (PI) indicating dead cells further confirms bactericidal nature. The enterocin LD3-treated cells showed higher infrared absorbance at 1451.82 cm− 1 corresponding to phospholipids suggesting membrane-acting nature of the bacteriocin. However, plantaricin LD4-treated cells did not show such alterations suggesting different mode of action. Both bacteriocins caused disruption and shrinkage of target cells, and leakage of intracellular contents as observed in transmission electron microscope (TEM). The present study suggests killing of S. aureus in milk, therefore, enterocin LD3 and plantaricin LD4 may be applied in biopreservation of milk and related food products.
KeywordsEnterocin LD3 Plantaricin LD4 Bactericidal Staphylococcus aureus Milk
The authors acknowledge the financial supports from the Department of Biotechnology (DBT, BT/PR8306/ PID/6/ 738/ 2013) and Indian Council of Medical Research (ICMR, 5/9/1117/2013-NUT), New Delhi, India. PS was supported by DBT fellowship and University Research Scholarship (URS), Department of Genetics, Maharshi Dayanand University, Rohtak.
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Conflict of interest
The authors declare that they have no conflict of interest.
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