Abstract
Simple SummaryFollowing the spread of antibiotic resistance and the high consumption of chicken meat, conventional poultry-producing companies have turned to antibiotic-free and organic lines of products. Our work investigated E. coli susceptibility to different antimicrobials and extended-spectrum β-lactamase (ESBL) E. coli diffusion from samples collected in slaughterhouse from conventional (C), organic (O) and reared without antibiotics (ABF) chickens. Conventional samples showed the highest number of E. coli strains resistant to ampicillin (89.6%), trimethoprim/sulfamethoxazole (62.2%), nalidixic acid (57.8%), ciprofloxacin (44.4%), and cefotaxime (43.7%), with prevalent patterns of multi-resistance to three (35.1%) and to four antimicrobials (31.3%). The highest numbers of ESBL E. coli were observed in conventional and the lowest in organic. Our results are relevant with an influence of farming typology regarding the susceptibility of E. coli and the presence of ESBL E. coli. Conventional farms, in which the use of antibiotics is allowed, showed samples with the highest number of strains resistant to antimicrobials commonly used in poultry as well as the highest amounts of ESBL E. coli. Organic samples exhibited the lowest value for ESBL due to a lack of antimicrobial treatment in chickens and the possibility to have access to the outdoors, limiting contact with litter as a potential source of resistant bacteria.As a result of public health concerns regarding antimicrobial resistance in animal-based food products, conventional poultry companies have turned to ‘raised without antibiotics’ (ABF) and organic farming systems. In this work, we evaluated the influence of rearing systems on antimicrobial susceptibility in E. coli and extended-spectrum β-lactamase (ESLB) E. coli diffusion in conventional (C), organic (O) and antibiotic free (ABF) chicken samples collected from cloacal swabs and skin samples in slaughterhouse. The E. coli isolates from conventional (135), antibiotic-free (131) and organic (140) samples were submitted to the Kirby–Bauer method and ESBL E. coli were analyzed by the microdilution test. Conventional samples showed the highest number of strains resistant to ampicillin (89.6%; p < 0.01), cefotaxime (43.7%; p < 0.01), nalidixic acid (57.8%; p < 0.01), ciprofloxacin (44.4%; p < 0.001), and trimethoprim/sulfamethoxazole (62.2%; p < 0.01), with patterns of multi-resistance to three (35.1%) and to four antimicrobials (31.3%), whereas most of the E. coli isolated from antibiotic-free and organic chicken samples revealed a co-resistance pattern (29.2% and 39%, respectively). The highest number of ESBL E. coli was observed in conventional, in both cloacal and skin samples and the lowest in organic (p < 0.001). Our results are consistent with the effect of conventional farming practices on E. coli antimicrobial resistance and ESBL E. coli number, due to the use of antimicrobials and close contact with litter for most of the production cycle.
Highlights
The indiscriminate use of antibiotics in poultry has contributed to a progressive increase in bacterial resistance to the main classes of antibiotics such as quinolones, tetracyclines and beta-lactams [1,2].In addition, the continued exposure of bacterial strains to a large variety of β-lactams has produced the mutation of bacterial β-lactamases, expanding their activity against the newly developed β-lactam antibiotics
E. coli was observed for ampicillin (76.6%), followed by tetracycline (68.4%), nalidixic acid (43.6%), trimethoprim/sulfamethoxazole (40.1%), and amoxicillin/acid clavulanic (35.7%)
Comparing isolate susceptibility on the basis of rearing system (Table 1), the highest levels of resistance for ampicillin (89.6%; p = 0.002), cefotaxime (43.7%; p = 0.001), nalidixic acid (57.8%; p = 0.001), ciprofloxacin (44.4%; p < 0.001) and trimethoprim/sulfamethoxazole (62.2%; p > 0.001) were observed in E. coli isolated from conventional chicken samples
Summary
The continued exposure of bacterial strains to a large variety of β-lactams has produced the mutation of bacterial β-lactamases, expanding their activity against the newly developed β-lactam antibiotics These enzymes are known as extended-spectrum β-lactamases (ESBLs). The genes responsible for resistance are frequently localized in transferable genetic elements such as plasmids and integrons [4,5,6,7], and pathogen and commensal E. coli can receive antimicrobial resistance genes and transmit them to other bacteria of the intestinal microbiota by conjugation [8,9,10] In this scenario, commercial chickens and turkeys are considered an important reservoir of E. coli and ESBL multiresistant isolates for humans [11,12]. The control of poultry diseases, especially for E. coli, relies on the use of autogenous vaccines [17] and on the quality of the environment which the typology of farms is focused [18,19]
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