Our aim was to monitor the resistance of Campylobacter isolates from two initial stages of broiler production in 5 grandparent breeder broiler farms (GPBFs) and 12 parent breeder broiler farms (PBFs) in which no antimicrobials were used during the study. Susceptibility tests were carried out for 805 strains (697 Campylobacter jejuni and 108 Campylobacter coli) against nalidixic acid, ciprofloxacin, erythromycin, amoxicillin, amoxicillin plus clavulanic acid, tetracycline, gentamicin, and chloramphenicol using the disk-diffusion method. Quinolone resistance was the most abundant overall (74.9%) and at each stage of production. The second largest resistance was for tetracycline with 48.2%. The resistance against amoxicillin plus clavulanic acid, gentamicin, and chloramphenicol was not found. The percentages of resistance and multidrug-resistant (MDR) isolates were always higher in the PBFs than in the GPBFs. However, pan-susceptible populations (total 10.3%) were isolated in our survey. C. coli isolates were more resistant to tetracycline and erythromycin (96.3% and 23.1%, respectively) than for C. jejuni (40.7% and 0%, respectively) and were more MDR (33.3% vs. 11.9%). In conclusion, as other authors have shown, even in the absence of antibiotic pressure, relatively high rates of quinolone resistance are found in Campylobacter. However, a decrease in quinolone resistance has been observed compared to other studies in Spain [i.e., 99%; Saenz et al. Antimicrob. Agents Chemother. 2000;44(2):267-271]. MDR, fluoroquinolone-, macrolide-, and tetracycline-resistant Campylobacter populations are issues of concern in public health.

The aim of this study was to investigate the resistance mechanisms of quinolones, macrolides and tetracycline in campylobacter isolates from grandparent and parent broiler breeders in Spain. Twenty-six isolates were investigated for quinolone resistance, three isolates for macrolide resistance and 39 for tetracycline resistance. All of the quinolone-resistant isolates possessed the mutation Thr86Ile in the quinolone resistance-determining region of gyrA and one isolate possessed the mutation Pro104Ser. Only one Campylobacter coli population (defined by restriction fragment length polymorphism-polymerase chain reaction of flaA and pulsed field gel electrophoresis) was resistant to erythromycin, and the mutation A2075G (23S rDNA) was responsible for macrolide resistance. The tetO gene was found in all of the tetracycline-resistant isolates. Twenty-two out of the 39 isolates investigated by Southern blot possessed chromosomic location of tetO and 17 were located on plasmids. Most of the plasmids with tetO were of around 60 kb and conjugation was demonstrated in a selection of them. In conclusion, we showed that Thr86Ile is highly prevalent in quinolone-resistant isolates as well as mutation A2075G in macrolide-resistant isolates of poultry origin. More variability was found for tetO. The possibility of horizontal transmission of tetO among campylobacter isolates is also an issue of concern in public health.

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