89D-18

E. PONCE-ALQUICIRA¹, L. Alquicira-Páez, F. J. Fernández-Perrino, I. Guerrero-Legarreta, and C. Wacher-Rodarte⁵. (1) Dept. de Biotecnología, Univ. Autónoma Metropolitana, Iztapalapa, Apartado Postal 55-535, Mexico D.F., 09340, Mexico, (2) Alimentos y Biotecnología, Facultad de Química, UNAM

Pediocin-like bacteriocins are antimicrobial peptides with high antilisterial activity. However, induction of spontaneous resistant Listeria strains has been reported when this strain grows at high bacteriocin levels. The objective of this was to study the effect of a bacteriocin produced by Pediococcus parvulus on the growth and resistance of Listeria strains. Bacteriocin activity was analyzed by the well diffusion method using L. innocua ATCC33090 as target microorganism. Resistance was studied for L. innocua and L. monocytogenes strains (scott-A, LM82, LBM-92000/48 and LBM-911204/47). Overnight cultures (BHI broth, pH 6.5, 37ºC) were diluted to a OD_600nm=0.002 (10⁵CFU/mL), added with various levels (0.1 to 1.2 mg/mL) of the P. parvulus freeze-dried bacteriocin (1300UA/mg), and incubated for 24 h at 37º C, with agitation at 150 rpm. Changes in OD_600nm were followed every 3 h to obtain maximum specific growth rate (Numax, h^-1), lag time (t-lag, h), and duplication time (t-d, h). Controls had no bacteriocin. Addition of bacteriocin (from 0.1 up to 0.8 mg/mL) reduced the growth rate for all Listeria strains tested, with the exception of L. monocytogens LM82, also resistant to streptomycin. Specific growth rate was half reduced from 0.7 to 0.38 h^-1, t-d increased twice from 0.99 to 1.83 h, and t-lag varied from 3.02 to 7.91 h. However, at high bacteriocin levels (1.2mg/mL), L. innocua ATCC33090 and L. monocytogenes scott-A did not show inhibition. L. monocytogenes LM82, LBM 911204/47 and LBM 92000/48 growth parameters were very similar to those in control samples; but t-lag values for these three strains were extended from 5 to 8.55, 10.5 and 7.49 h, respectively. Therefore pediocin antilisterial activity varies among different Listeria strains; high concentrations may induce spontaneous resistance.

Session 89D, Food Microbiology: Antimicrobial effects on foodborne microorganisms
2:00 PM - 5:30 PM, Tuesday PM Room Hall I-2

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana