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. 2015 Apr;52(4):2148-56.
doi: 10.1007/s13197-013-1214-5. Epub 2013 Dec 3.

Enhanced bactericidal effect of enterocin A in combination with thyme essential oils against L. monocytogenes and E. coli O157:H7

Taoufik Ghrairi  1 , Khaled Hani  1
Affiliations

Enhanced bactericidal effect of enterocin A in combination with thyme essential oils against L. monocytogenes and E. coli O157:H7

Taoufik Ghrairi et al. J Food Sci Technol. 2015 Apr.

Abstract

The combined effects of enterocin A with Thymus vulgaris essential oils (EOs) against Listeria monocytogenes and Escherichia coli O157:H7 were investigated in vitro by enumeration of surviving populations of testing pathogens and minimal inhibitory concentration (MIC) determination. Enterocin A was purified to homogeneity by RP-HPLC from the culture fluid of Enterococcus strain and thyme EOs were extracted from local Thymus vulgaris plants. The major constituent of thyme EOs oils determined by GC-MS was thymol (78.4 %). Combination of enterocin A with thyme EOs showed an enhanced bactericidal effect against Listeria monocytogenes. Checkerboard assay and isobologram construction displayed a synergistic interaction between these compounds against Listeria (FIC index <0.5). Moreover, the MIC value of enterocin A has fallen fivefold (from 4.57 to 0.9 μg/ml), while the MIC of thyme EOs decreased threefold (from 3.6 to 1.2 μg/ml). Treatments with enterocin A alone did not affect the growth of the enteric pathogen E. coli O157:H7. However, the addition of thyme EOs and enterocin A yielded a synergistic antimicrobial effect against E. coli (MIC thyme EOs decrease from 2.2 to 0.71 μg/ml). This is the first report on the combined effect of enterocin A and thyme EOs against food pathogen bacteria. This combination could be useful in food bio-preservation.

Keywords: Bacteriocins; E. coli; Essential oils; Food preservation; Lactic acid bacteria; Listeria.

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Figures

Fig. 1
Fig. 1
Chromatogram of T. vulgaris essential oil
Fig. 2
Fig. 2
Final RP-HPLC of purified enterocin A from E. faecium MMT21 strain. Dark arrow indicates the active fraction against L. monocytogenes. The purified peptides were applied to C18 column and eluted using a linear gradient of acetonitrile (15–80 %) containing 0.1 % TFA at a flow rate 1 ml/min
Fig. 3
Fig. 3
Growth of L. monocytogenes EGDe (a) and E. coli O157:H7 (b) in BHI broth in the presence of enterocin A, thyme EOs and both. The concentration of each agent is 1/2 MIC except for E. coli test. Results were obtained from duplicate. Enterocin A (diamond), thyme EOs (white square), EntA + thyme EOs (triangle), blank test (white circle)
Fig. 4
Fig. 4
Isobologram of enterocin A and thyme oils against L. monocytogenes EGDe
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