In vitro inhibition of soft-rotting bacteria by EDTA and nisin and in vivo response on inoculated fresh cut carrots.
Wells, J.M., Liao, C.-H. and Hotchkiss, A. T.
Plant Disease. Volume 82, Number 5, May 1998. Pages 491-495.
1998
บทคัดย่อ
EDTA and the antibiotic nisin, in combination with heat, were tested for inhibition of growth of six pectolytic, soft-rotting bacteria in 80% trypticase soy broth (TSB). Fifty percent reduction of growth by EDTA at 25 degrees C in TSB occurred at 3.24 mM for Erwinia chrysanthemi, 2.57 mM for Pseudomonas fluorescens, 0.96 mM for E. carotovora (subsp. carotovora), 0.48 mM for P. viridiflava, 0.17 mM for Xanthomonas campestris (pv. campestris), and 0.16 mM for Cytophaga johnsonae. Nisin at 50 micrograms/ml was effective against X. campestris and C. johnsonae (over 90% inhibition of growth) but not against the other four bacteria (less than 20% inhibition), which are the more economically important soft-rotters. Combinations of EDTA and nisin were synergistic. A combination of 0.3 mM EDTA + nisin at 50 micrograms/ml inhibited growth of E. carotovora, E. chrysanthemi, and P. viridiflava by over 70%, and growth of P. fluorescens by 37%. Hot water treatments for 0.3 min at 37 or 49 degrees C reduced survival of bacteria in the presence of EDTA + nisin, but not of EDTA, nisin, or water alone. EDTA + nisin at 37 degrees C reduced CFU/ml of E. carotovora, E. chrysanthemi, P. fluorescens, and P. viridiflava by 2 log units, and at 49 degrees C by 3 log units, compared with the 25 degrees C treatment. Decay of carrot disks inoculated at two inoculum levels (10(3) and 10(4) CFU per disk) with E. carotovora, P. fluorescens, or P. viridiflava was reduced by a 1.5-min immersion in 45 degrees C water, with or without EDTA and nisin additives. Immersion in 0.3 mM EDTA + nisin at 15 to 50 micrograms/ml at 45 degrees C reduced decay due to E. carotovora and to P. fluorescens at the lower inoculum level by an average of about 50% compared with water alone at 45 degrees C, but differences were statistically significant only at the 90% level of confidence and no different than a standard chlorine dip, current commercial practice for cut carrot slices.