Reduction of Escherichia coli population following treatment with bacteriocinsw from lactic acid bacteria and chelators.

CAROLINA BELFIORE; PATRICIA CASTELLANO; GRACIELA VIGNOLO

FOOD MICROBIOLOGY

Elsevier

Lugar: Amsterdam, The Netehrlands; Año: 2007 vol. 24 p. 223 - 229

0740-0020

The use of lactocin 705 and AL705 (2100 AU/ml), two bacteriocins produced by Lactobacillus curvatus CRL705 and nisin (1000 AU/ml) produced by Lactococcus lactis CRL1109 to inactivate two Escherichia coli strains in TSB medium at 21 and 6ºC was investigated. Direct and deferred strategies using various chelating agents were assayed. Treatment with EDTA (500 and 1000 mM) and Na lactate (800 mM) alone produced a variable effect depending on the strain, Na lactate being inhibitory against E. coli NCTC12900 at both assayed temperatures while EDTA (1000 mM) led to inactivation of this strain only at 6ºC. When bacteriocins and chelators were evaluated, E. coli NCTC12900 demonstrated to be more sensitive than E. coli G2 to the deferred addition of EDTA and Na lactate in combination with lactocin 705/AL705 and nisin at 6ºC and 21ºC. The direct addition of bacteriocins and chelators was not as effective as compared to deferred treatments. However, deferred treatment effectiveness at 6º C was highly dependent on strain sensitivity, E. coli G2 being more resistant to bacteriocin/chelator combinations, while E. coli NCTC12900 was totally inhibited with EDTA (500 and 1000 mM) combined with both bacteriocins. Of the Na lactate/bacteriocins combinations the addition of lactocin 705/AL705 was the most effective for reducing viable counts of NCTC12900 strain to zero after 14 days at 6ºC. Nevertheless, lactocin 705/AL705 was the most effective antimicrobial compound inhibiting both strains at 6 and 21ºC. Sensitization of the outer membrane of Gram-negative bacteria with EDTA and Na lactate, may be of value in controlling Escherichia coli in foods in combination with bacteriocinogenic strains.