Study of comparative therapeutic and prophylactic efficacy of fluoroquinolone antibiotics in experimental staphylococcosis of day-old chicks

Staphylococcosis in chicks raises much concern among poultry industry specialists and improving methods of its containing is still an urgent problem. We conducted a comparative study as for therapeutic and prophylactic efficacy of several fluroquinolone drugs in chicks, experimentally infected with Staphylococcus aureus . The chicks were challenged intraperitoneally with two different field isolates of S. aureus in suspension. One of the two isolates was resistant to fluoroquinolones, the other was susceptible to them. The chicks began receiving the drugs via drinking water ad libitum at 48 h prior to the challenge, at a concentration 200 mg/L. The treatment lasted 5 days. The results of our study show that the highest therapeutic effectiveness (96% and 88%) was achieved in the groups, which had been challenged with an S. aureus strain, susceptible to fluoroquinoloes and treated with enrofloxacin and levofloxacin, respectively. In the group, which had been challenged with a susceptible strain and treated with ciprofloxacin, therapeutic effectiveness was as just high as 68%. The results of our study also show rather low effectiveness of ofloxacin p.o. for treatment of staphylococcosis in chicks. When the chicks had been challenged with an S. aureus strain, resistant to fluoroquinolones, the mortality rate was as high as 96%. When they had been challenged with an S. aureus strain, susceptible to ofloxacin, the mortality rate of the poultry was rather high too - 52%. For most of the chicks in this group the infection became chronic, making the prospects of their treatment and subsequent use in the farm obscure. Administration of norfloxacin proved its low effectiveness, very much like ofloxacin. For the two groups, receiving norfloxacin, the mortality rate among the challenged chicks was as high as 80% and 76%, respectively.