Many antibiotics have been extensively used in feed and water medication of poultry or in egg injection or egg dipping programmes. Over the years resistance problems have developed for some antibiotics, making their use unreliable and sometimes ineffective. Authorities have imposed longer withdrawal times and bans on antibiotics, which are cross resistant with antibiotics used in human medicine. Depending on the molecule, resistance may develop more or less quickly. Testing of mycoplasma strains worldwide reveal a variation in MICs (minimal inhibitory concentration). The MIC value should be below the maximum concentration in the serum (Cmax) to allow for an effective cure. If MIC values are above maximum concentrations in the serum, resistance of the bacteria has reached levels, at which the prescribed dose does not inhibit the bacteria. Thus, either the dose needs to be increased or the mycoplasma will continue to cause damage and infect other birds. A comparison of highest Cmax and highest MICs, published for various antibiotics is given in the table below. Both Tiamutin and danofloxacin have MICs below the Cmax. This means that normal doses of these products are likely to be effective against MG and MS, in contrast to the competitor products.
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M. Valks and others, 2002 |
| Comparison of Cmax and steady state levels with MIC ranges of various antimicrobials against MG and MS |
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