Antibiotic Resistance Genes Occurrence in Conventional and Antibiotic-Free Poultry Farming, Italy

Abstract

Antimicrobial resistance is a complex and widespread problem threatening human and animal health. In poultry farms, a wide distribution of resistant bacteria and their relative genes is described worldwide, including in Italy. In this paper, a comparison of resistance gene distribution in litter samples, recovered from four conventional and four antibiotic-free broiler flocks, was performed to highlight any influence of farming systems on the spreading and maintenance of resistance determinants. Conventional PCR tests, targeting the resistance genes related to the most used antibiotics in poultry farming, along with some critically important antibiotics for human medicine, were applied. In conventional farms, n. 10 out of n. 30 investigated genes were present in at least one sample, the most abundant fragments being the tet genes specific for tetracyclines, followed by those for aminoglycosides and chloramphenicol. All conventional samples resulted negative for colistin, carbapenems, and vancomycin resistance genes. A similar trend was observed for antibiotic-free herds, with n. 13 out of n. 30 amplified genes, while a positivity for the mcr-1 gene, specific for colistin, was observed in one antibiotic-free flock. The statistical analysis revealed a significant difference for the tetM gene, which was found more frequently in the antibiotic-free category. The analysis carried out in this study allowed us to obtain new data about the distribution of resistance patterns in the poultry industry in relation to farming types. The PCR test is a quick and non-expensive laboratory tool for the environmental monitoring of resistance determinants identifying potential indicators of AMR dissemination.

Microbial Community and Abundance of Selected Antimicrobial Resistance Genes in Poultry Litter from Conventional and Antibiotic-Free Farms

“…Similarly, a more recent work highlighted that the abundance of tetracycline genes was not influenced by the use of grown promoting doses of antimicrobials, even if the aminoglycoside resistance genes tended to be higher in the broiler supplemented with chlortetracycline [ 29 ]. Other studies confirmed that the use of therapeutic doses of antibiotics in poultry farming increases the total ARGs load in intestinal tracts [ 15 ], even if the antibiotic-free farms had a wide distribution of resistant bacteria and related ARGs, as already observed in different geographical areas [ 23 , 42 , 43 ]. Noteworthy, most ARGs, including those investigated in this study, can be located in mobile genetic elements (MGE) as plasmids, trasposons, or insertion sequences, and they are able to move in different microbial niches, conferring the antimicrobial resistance profiles to different bacterial species and allowing for the accumulation and dissemination of resistant microorganisms in the environment [ 44 ].…”

“…The quantitative polymerase chain reaction (qPCR) was applied to find a panel of ARGs related to the antibiotics commonly used in conventional farming or those critically important in human medicine. Specifically, the target fragments aad A2 for aminoglycosides, tet (A), tet (B), tet (K), and tet (M) for tetracyclines, and mcr -1 for colistin were selected, considering analogous investigations previously carried out in the same area of study [ 23 ]. The above-mentioned fragments were quantified with SYBR Green ® qPCR protocols, as previously described [ 57 , 58 ], using a Magnetic Induction Cycler (Mic) real-time machine (BMS, Australia).…”

“…In addition, chicken litter is frequently used as organic fertilizer to enrich soils and crops, representing a source of environmental dissemination of antimicrobial-resistant bacteria and the relative genes [ 17 ]. The microbial composition of poultry litter has been deeply investigated with respect to any spatial or temporal modifications that can occur during the farming cycles or composting phases [ 17 , 18 , 19 , 20 , 21 ], but only few of studies focused on the modification of fecal microbioma and resistome in relation to the use of antibiotics during the rearing of animals, comparing both conventional and antibiotic-free systems [ 15 , 22 , 23 ].…”

Colistin Resistance Genes in Broiler Chickens in Tunisia

“…This approach is more expensive than traditional cultivation and does not allow determination of the bacterial sources of resistance genes. However, it is a rapid method that avoids possible underestimation of the occurrence of AMR [ 44 ], as it is able to detect non-culturable or labile bacteria and provides more extensive information on the resistance patterns harboured by all bacteria present in the tested samples and not only those highlighted in selected colonies [ 45 ].…”

Antimicrobial Efficacy of Cinnamon Essential Oil against Avian Pathogenic Escherichia coli from Poultry

“…Therefore, the poultry industry is currently focused on eliminating the use of antibiotics, thus seeking innovative management systems [ 30 ]. The production of antibiotic-free broiler has increased due to consumer perception that poultry meat is qualitatively superior to conventionally produced meat [ 31 , 32 ]. Alternative methods to antibiotics for the control of bacterial diseases in poultry farms could be natural substances such as some essential oils that, due to their potential antimicrobial properties, could find application in poultry phytotherapy [ 33 ].…”