Quinolone- and ß-lactam-resistance in Escherichia coli from Danish and Italian broiler flocks

Valeria Bortolaia¹, Luca Guardabassi¹, Magne Bisgaard¹, Marcello Trevisani², Anders Miki Bojesen¹

¹Department of Veterinary Pathobiology, Faculty of Life Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Denmark

²Dipartimento di Sanità Pubblica Veterinaria e Patologia Animale, Facoltà di Medicina Veterinaria, Università di Bologna, 40064 Ozzano Emilia (BO), Italy

The prevalence of quinolone- and ß-lactam-resistant E. coli was investigated among broiler flocks in Denmark and Italy. In Denmark, sock samples were collected from 10 parent flocks and 10 offspring flocks, according to the procedure currently used for the surveillance of Salmonella in the EU. Samples were enriched in McConkey broth and streaked on McConkey agar plates added with nalidixic acid (32 µg/ml), ciprofloxacin (2 µg/ml), ampicillin (32 µg/ml), cefotaxime (2 µg/ml) or ceftiofur (8 µg/ml). The ß-glucuronidase test was performed for verification of presumptive E. coli. The same methods were used to analyse sock samples collected from six Italian broiler flocks. PCR with primers for the CTX-M-type ESBLs was performed on cephalosporin-resistant isolates.

While resistance to ampicillin and nalidixic acid was widespread in both countries, resistance to ciprofloxacin and cephalosporins was more common among Italian flocks. In Denmark, ciprofloxacin resistance was only detected in one parent flock without any history of quinolone usage and none of the flocks was positive for cephalosporin-resistant E. coli. In Italy, resistance to ciprofloxacin was detected in all flocks and resistances to ceftiofur and cefotaxime were detected in five flocks. Primers specific for the CTX-M-type ESBLs generated PCR amplicons from isolates from three of these flocks.

Antimicrobial resistance in indicator E. coli from poultry is annually monitored in Denmark through collection of samples at slaughter and reported in DANMAP. In 2006, DANMAP reported a prevalence of indicator E. coli resistant to ampicillin, nalidixic acid and ciprofloxacin of 17,1%, 7,3 % and 5,7%, respectively. However, our study shows that resistance towards ampicillin and nalidixic acid is widespread at flock level. The low prevalence of ciprofloxacin-resistant E. coli and the absence of resistance to cephalosporins might be a consequence of the restricted use of antimicrobials in Danish poultry production. In Italy, a well established program for monitoring veterinary antimicrobial resistance is lacking, therefore the obtained data can not be discussed on a national basis. However, the common perception is that the use of broad-spectrum antimicrobials such as fluoroquinolones and cephalosporins in the Italian poultry production is higher compared to the Danish. Accordingly, the results of this study could reflect the different policies in antimicrobial usage between the two countries.