87-4 |
Enhanced inhibition of Escherichia coli O157:H7 by lysozyme and chelators |
J. BOLAND1, P. M. Davidson, and J. Weiss. (1) Colloidal and Interfacial Food Science Laboratory, University of Tennessee, 2605 River Drive, Room 102, Knoxville, TN 37996 EDTA with food antimicrobials, such as lysozyme or nisin, enhances their activity against Gram-negative bacteria by a mechanism that likely involves chelation of cations destabilizing the outer membrane. Since EDTA has limited approval for use in foods by US regulatory agencies, other GRAS chelators could expand the activity spectrum of compounds such as lysozyme. Disodium pyrophosphate and tripolyphosphate have divalent cation stability constants similar to EDTA. In addition, studies in our laboratories have demonstrated that lysozyme, partially denatured with ultrasound, may have better activity than native lysozyme. To investigate the effect of various chelators on antimicrobial efficacy of native and partially-denatured lysozyme against E.coli O157:H7. Native (N) and partially-denatured (PD) lysozyme, EDTA, disodium pyrophosphate (DP) and tripolyphosphate (TPP) were prepared at 200-500µg/ml. A microbroth assay was used to study the antimicrobial activity of combinations of lysozyme with chelators against four strains of Escherichia coli O157:H7. Absorbance was monitored over 48hrs. using a microplate reader to measure inhibition. N-lysozyme alone at concentrations <500µg/ml was not inhibitory to any of the four strains of E.coli O157:H7 after 12hrs. Upon addition of EDTA, two strains were completely inhibited by 500µg/ml of the combination while the remaining strains had increased lag phases. Activity of ultrasound-treated PD-lysozyme with EDTA was depending upon strain. DP was not as effective as EDTA but did slightly enhance activity of N-lysozyme for all strains except one (F4546). DP-inhibition varied significantly in combination with PD-lysozyme. Partial denaturation of lysozyme in general introduced strain-dependence suggesting that the protein structure affects antimicrobial efficacy. Results with TPP were similar to those for DP. Results indicate that addition of DP or TPP to lysozyme was not as effective as EDTA on an equal concentration basis at inhibiting the growth of Escherichia coli O157:H7 but that activity was slightly enhanced depending upon strain and compound.
Session 87, Food Microbiology: General
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