Antibiotic sensitivity tests on Escherichia coli isolated from poultry: significance of mixed strain inocula.
One hundred and ninety four Escherichia coli strains, isolated from birds received from 15 farms for post mortem examination and showing a variety of clinical pictures, have been tested for susceptibility to several drugs. From examination of several subcultures (colonies) from a particular organ it was concluded that there are great differences in susceptibility between strains isolated from the same organ, from different organs of the same bird or from different birds of the same flock. The effect of this phenomenon on the results of the sensitivity tests has been studied. For preparation of the inoculum it is preferable to use 20-100 colonies per organ. Moreover, it is recommended that in each examination several antibiograms of mixtures of strains isolated from organs of the same kind are included.
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Poultry Health Institute, Doom, The Netherlands.