Antibiotic treatment of nude rats and its impact on the aerobic bacterial flora.

A colony of nude rats were treated with the antibiotics ampicillin, spiramycin, sulfadoxine/trimethoprim, tetracycline, lincomycin and spectinomycin over a period of 30 weeks. The rats were monitored bacteriologically during the whole treatment period and for a period of 24 weeks after the treatment. Antibiograms of each isolated microorganism were made in vitro. The primary target, Pasteurella pneumotropica, was suppressed by the treatment, but reappeared after ending the medication. Klebsiella pneumoniae subsp. pneumoniae, never observed before the use of antibiotics in the colony, became one of the most common organisms in the colony. Furthermore, this bacterium was resistant to all antibiotics tested in vitro. Also other Enterobacteriaceae and some Streptococcaceae were propagated. Only Staphylococcus aureus seemed to have been eradicated by the treatment. It is concluded, that such antibiotic treatment does not necessarily improve the microbiological quality of the rats, and that it imposes a high risk of propagating resistant bacteria.