Prevalence and subtypes of ciprofloxacin-resistant Campylobacter spp. in commercial poultry flocks before, during, and after treatment with fluoroquinolones

Abstract

Five commercial broiler chicken flocks were treated with either difloxacin or enrofloxacin for a clinically relevant infection, as instructed by a veterinarian. Campylobacters were isolated from individual fecal samples and from samples associated with the broiler environment before, during, and after treatment. Ciprofloxacin-resistant Campylobacter jejuni and/or C. coli strains were detected pretreatment in four flocks, but they constituted a very small proportion of the campylobacters present. When the broilers were treated with a fluoroquinolone, a rapid increase in the proportion of ciprofloxacin-resistant campylobacters was observed. During treatment nearly 100% of campylobacters were resistant, and in some flocks a high proportion of resistant strains persisted for up to 4 weeks after treatment. Prior to treatment a variety of campylobacter subtypes were present. During and after treatment considerable changes in both species and subtype prevalence were observed, but no single fluoroquinolone-resistant clone became dominant. Instead, resistant C. coli strains or a mixture of resistant C. coli and C. jejuni strains became dominant, whereas susceptible C. jejuni strains had usually been dominant prior to treatment. The resistant subtypes which emerged and became dominant were not always the same as those detected pretreatment. The persistence of resistant strains for up to 4 weeks posttreatment has important implications for any strategy designed to avoid the introduction of such strains into the food chain.

FIG. 1.

Numbers of Campylobacter spp. in chicken feces collected before, during, and after fluoroquinolone treatment from a housed broiler flock on a commercial chicken farm (flock 4). Each bar represents an individual freshly voided fecal sample. Shading indicates the numbers of ciprofloxacin-resistant Campylobacter spp. estimated by replica plating onto Iso-Sensitest agar containing 1 μg of ciprofloxacin per ml, 10 μg of amphotericin B per ml, and 32 μg of cefoperazone per ml (see text). The detection limit for the numbers of resistant strains varied between the samples and is illustrated as a horizontal line through each bar. The > symbol over a bar denotes that the total number of campylobacters exceeded the detection limit indicated by the top of the bar.

FIG. 2.

Numbers of Campylobacter spp. in chicken feces collected before, during, and after fluoroquinolone treatment on a free-range commercial chicken farm (flock 5). Each bar represents an individual freshly voided fecal sample. Shading indicates the numbers of ciprofloxacin-resistant Campylobacter spp. estimated by replica plating onto Iso-Sensitest agar containing 1 μg of ciprofloxacin per ml, 10 μg of amphotericin B per ml, and 32 μg of cefoperazone per ml (see text). The detection limit for the numbers of resistant strains varied between the samples and is illustrated as a horizontal line through each bar. The > symbol over a bar denotes that the total number of campylobacters exceeded the detection limit indicated by the top of the bar.

FIG. 3.

Numbers of Campylobacter spp. in chicken feces collected before, during, and after fluoroquinolone treatment from a free-range commercial chicken farm (flock 6). Each bar represents an individual freshly voided fecal sample. Shading indicates the numbers of ciprofloxacin-resistant Campylobacter spp. estimated by replica plating onto Iso-Sensitest agar containing 1 μg of ciprofloxacin per ml, 10 μg of amphotericin B per ml, and 32 μg of cefoperazone per ml (see text). The detection limit for numbers of resistant strains varied between samples and is illustrated as a horizontal line through each bar.