Fate of Escherichia coli during Ensiling of Wheat and Corn

• Published in: Applied and Environmental Microbiology Vol. 71; no. 9; pp. 5163 - 5170
• Main Authors: Chen, Y, Sela, S, Gamburg, M, Pinto, R, Weinberg, Z. G
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.09.2005
• Subjects: acidification; Bacteria; Biological and medical sciences; Colony Count, Microbial; Corn; corn silage; crop residues; Culture Media; Drug Resistance, Bacterial - genetics; Escherichia coli; Escherichia coli - drug effects; Escherichia coli - genetics; Escherichia coli - growth & development; Escherichia coli - isolation & purification; Fermentation; Fluorescence; Fundamental and applied biological sciences. Psychology; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Hydrogen-Ion Concentration; inactivation; Microbial Ecology; Microbiology; pathogen survival; Proteins; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Silage - analysis; Silage - microbiology; silage fermentation; silage making; Triticum - microbiology; Triticum aestivum; Wheat; Zea mays - microbiology; Corn; Bacteria; Silage; Wheat; Escherichia coli; Enterobacteriaceae
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.71.9.5163-5170.2005

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 x 10⁸ 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.