Fate of Escherichia coli during ensiling of wheat and corn.

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 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.

The passage of lactic acid bacteria from silage into rumen fluid, in vitro studies.

Inoculated silages sometimes improve cattle performance, possibly because of probiotic effects of lactic acid bacteria (LAB) silage inoculants. The cause of improved animal performance following feeding with inoculated silage is unclear. One issue in studying this phenomenon is to find out whether LAB pass from silage into the rumen fluid and survive in it. The purpose of the present study was to determine whether LAB from inoculated and uninoculated silages pass into the rumen fluid in vitro. Wheat and corn silages, uninoculated or inoculated with 1 of 10 commercial silage inoculant LAB, were prepared in glass jars. After ensiling, a 2.5-g silage sample was added to 25 mL of heat-sterilized or strained rumen fluid together with 5 g/L glucose, and incubated for 48 h at 39 degrees C. Analysis of the incubated rumen fluid included pH measurement, enumeration of LAB, and determination of lactic acid and volatile fatty acids (VFA). The pH of the rumen fluid decreased during incubation; both heat-sterilized and strained rumen fluid contained large numbers of LAB. The heat-sterilized rumen fluid contained lactic acid in addition to VFA, whereas the strained rumen fluid contained only VFA. The results indicate that LAB pass from silage samples into the rumen fluid in vitro and survive there. Their interactions with rumen microorganisms should be studied further to understand how some silage inoculant LAB exhibit probiotic effects in dairy cattle.

[Effect of Bac. intermedius RNAse on a cell population of ascitic lympholeukemia NKLy]. / Vliianie RNKazy Bac. intermedius na populiatsiiu kletok astsitnogo limfoleikoza NKLy.

RNAase of Bac. intermedius and a modification of this enzyme containing a histidine-inactivated active site were studied for their influence on the activity of proliferation of murine ascitic lympholeukemia cells (NKLy) using a 3H thymidine label. Each mouse received a single intraperitoneal injection (dosage 1 mg per kg) of the normal or inactivated enzyme. It was shown that irrespective of the catalytic activity both enzyme preparations decreased the proliferative activity of the cells, blocked G2-M, slowed the course of the prophase and metaphase of meiosis, diminished the number of cells synthetizing DNA and lowered the intensity of labelling. After 24 hours all these characteristics returned to normal.