ABSTRACT
Quinolones are broad-spectrum antibacterial agents used in human and veterinary medicine, and their extensive use have been associated with a rise of the quinolone resistance. In the present study, the quinolone resistance of avian E.coli and Salmonella isolates was evaluated and compared, in which 344 avian E.coli and 224 Salmonella isolates from 1990s were serogrouped with antisera and thc antimicrobial susceptibility test to 10 quinolones was carried out by using the Kirby-Bauer method recommended by Clinical and Laboratory Standards Institute (CLSI). It was demonstrated that the 344 isolates of avian E.coli distributed in 27 serogroups and 68.90% (237/344) of the isolates belonged to four O-serogroups: i.e. O1, O2, O18, O78, and the 224 isolates of avian Salmonella were all determined to be Salmonella pullorum. The drug-resistance rate of avian E. coli isolates to nalicixic acid from 1993-1999 was more than 60%(64.43%,131/181), whereas those of isolates to 9 antibiotics from 2000-2008 had a drug-resistance rates of more than 60%, namely,nalicixic acid(92.02%), fleroxacin(79.75%), pipemidic acid(79.14%), enrofloxacin(78.53%), enoxacin(76.07%), lomenfloxacin(74.85%), ciprofloxacin(69.33%), norfloxacin(63.80%) and ofloxacin(61.35%). For the 4 O-serogroups of the avian E.coli isolates, the drug-resistance rates of more than 50% to antimicrobials were as follows: O78 isolates to 7 antimicrobials;O18 isolates to 5 antimicrobials, and O1 and O2 isolates just to 3 antimicrobials. The quinolone resistance of Salmonella isolates was much lower than E.coli, in which 101 salmonella isolates from 1993-1999 were all susceptible to quinolones. Nalicixic acid resistance of salmonella isolate firstly appeared in 2000, and the drug-resistance rate of salmonella isolates from 2000-2008 was found to be more than 60% for nalicixic acid(83.74%), but those to other quinolones were comparatively lower. These results indicated that the quinolone resistance of avian E.coli and salmonella were increasing in the past two decads because of the over-use of antibiotics.