Affiliation:
1. Department of Food Science, The Volcani Center, Bet Dagan 50250, Israel
Abstract
ABSTRACT
A recombinant
Escherichia coli
strain carrying a plasmid with an antibiotic resistance marker and expressing the green fluorescent protein was inoculated at a concentration of 3.8 × 10
8
CFU/g into direct-cut wheat (348 g of dry matter kg
−1
), wilted wheat (450 g of dry matter kg
−1
), and corn (375 g of dry matter kg
−1
). The forages were ensiled in mini-silos. The treatments included control (no
E. coli
added), application of tagged
E. coli
, and delayed sealing of the inoculated wheat. Three silos per treatment were sampled on predetermined dates, and the numbers of
E. coli
were determined on Chromocult TBX medium with or without kanamycin. Colonies presumptively identified as
E. coli
were also tested for fluorescence activity. Addition of
E. coli
at the time of ensiling resulted in a more rapid decrease in the pH but had almost no effect on the chemical composition of the final silages or their aerobic stability.
E. coli
disappeared from the silages when the pH decreased below 5.0. It persisted longer in silages of wilted wheat, in which the pH declined more slowly. Control silages of all crops also contained bacteria, presumptively identified as
E. coli
, that were resistant to the antibiotic, which suggests that some epiphytic strains are naturally resistant to antibiotics.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
19 articles.
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