Minimal inhibitory concentration of ofloxacin and its efficacy in experimental infection of chicks with salmonella infantis

The goal of the present article was to study minimal inhibitory concentrations (MIC) of ofloxacin with regard to its efficacy in experimental infection of chicks with Salmonella infantis. Values of MIC of ofloxacin for S. infantis were procured with the help of HiComb Strip test. The results of the tests in vitro, aimed at securing the values of minimal inhibitory concentrations of ofloxacin, prove that the drug boasts high antibacterial activity against most strains of S. infantis. Thus, ofloxacin inhibited the growth of the aforementioned microorganism at concentrations within the interval 0.005 – 0.05 μg/mL. Though one of the isolates proved to be resistant to the drug, its MIC was as high as 1.5 μg/mL. We employed day -old chicks in our experiment, which we conducted in order to evaluate the therapeutic and prophylactic effects of ofloxacin. For the sake of the experiment, we divided 250 chicks in 2 groups with 5 subgroups in either of them (n = 25 in each subgroup). For the experimental infection we used 2 strains of S. infantis, with different minimal inhibitory concentrations of ofloxacin, which had been detected previously. The chicks were challenged intraperitoneally with S. infantis in suspension, incubated on agar medium for 24 hours, at a concentration 3 x 10⁸ CFUs / 0.5 mL. The chicks in Group I were challenged with a strain with minimal inhibitory concentration of ofloxacin 0.05 μg/mL, the chicks in Group II - 1.5 μg/mL. The treatment with ofloxacin started 24 hours prior to the challenge and lasted 5 days. The drug was administered via drinking water ad libitum at concentrations 25 mg/L, 50 mg/L, 100 mg/L, 200 mg/L in both groups. The results of the experiment show that after the challenge of chicks with an S. infantis strain, susceptible to ofloxacin, the drug has high therapeutic and prophylactic effects at concentrations 100 mg/L and 200 mg/L (88 % and 96 % respectively). But in experimental infection of chicks with an S. infantis strain, resistant to ofloxacin, its administration at the above-mentioned concentrations did not lead to positive effect.

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