Abstract
The colonization of broilers with extended-spectrum β-lactamase- (ESBL-) and plasmid-mediated AmpC β-lactamase- (pAmpC-) producing Enterobacteriaceae has been extensively studied. However, only limited data on intervention strategies to reduce the colonization throughout the fattening period are available. To investigate practically relevant management measures for their potential to reduce colonization, a recently published seeder-bird colonization model was used. Groups of 90 broilers (breed Ross 308) were housed in pens under conventional conditions (stocking of 39 kg/m2, no enrichment, water and feed ad libitum). Tested measures were investigated in separate trials and included (I) an increased amount of litter in the pen, (II) the reduction of stocking density to 25 kg/m2, and (III) the use of an alternative broiler breed (Rowan x Ranger). One-fifth of ESBL- and pAmpC- negative broilers (n = 18) per group were orally co-inoculated with two E. coli strains on the third day of the trial (seeder). One CTX-M-15-positive E. coli strain (ST410) and one CMY-2 and mcr-1-positive E. coli strain (ST10) were simultaneously administered in a dosage of 102 cfu. Colonization of all seeders and 28 non-inoculated broilers (sentinel) was assessed via cloacal swabs during the trials and a final necropsy at a target weight of two kilograms (= d 36 (control, I-II), d 47 (III)). None of the applied intervention measures reduced the colonization of the broilers with both the ESBL- and the pAmpC- producing E. coli strains. A strain-dependent reduction of colonization for the ESBL- producing E. coli strain of ST410 by 2 log units was apparent by the reduction of stocking density to 25 kg/m2. Consequently, the tested management measures had a negligible effect on the ESBL- and pAmpC- colonization of broilers. Therefore, intervention strategies should focus on the prevention of ESBL- and pAmpC- colonization, rather than an attempt to reduce an already existing colonization.
Highlights
Antibiotic resistance is an increasing threat to global public health and concerns human- and veterinary medicine [1]
Compared to the control group for the ESBL- E. coli strain, a reduced hazard of colonization was solely apparent under the reduction of stocking density to 25 kg/ m2, with a hazard ratio (HR) of 0.18
A reasonable explanation is that the reduced bacterial contamination per square meter of the litter caused the effect on colonization [24]
Summary
Antibiotic resistance is an increasing threat to global public health and concerns human- and veterinary medicine [1]. Broiler chickens are considered as a reservoir for ESBL- and pAmpC- producing bacteria, it with frequently confirmed high prevalence [3, 4]. These antibiotic-resistant bacteria are detected at every level of the broiler production chain. Various transmission routes are described for ESBL- and pAmpC- producing bacteria. Recent findings have shown that 101 to 102 colony forming units (cfu) of orally administered ESBL- and pAmpC- producing E. coli can already lead to colonization of broiler chickens [12, 13]. A reduction of the microbial load through intense cleaning and disinfection processes cannot eliminate ESBL- and pAmpC- producing bacteria and the recirculation of resistant bacteria from earlier production rounds could play a role in contaminating the consecutive flock [5]
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