Antibiotic resistance genes load in an antibiotic free organic broiler farm

Abstract

Antibiotic resistance is a serious concern for public health. Farm environments are relevant reservoirs of antibiotic resistant bacteria and antibiotic resistance genes ( ARGs ), thus strategies to limit the spread of ARGs from farms to the environment are needed. In this study a broiler farm, where antibiotics have never been used for any purpose, was selected to evaluate if this measure is effective in reducing the ARGs load in farm environment ( FE ) and in meat processing environment ( MPE ). Faecal samples from FE and MPE were processed for DNA extraction. Detection and quantification of the 16S rRNA gene and selected ARGs ( bla TEM , qnr S, sul 2, and tet A) were carried out by PCR and digital droplet PCR ( ddPCR ), respectively. Generally, the relative abundance of the quantified ARGs in FE was similar or higher than that measured in intensive farms. Furthermore, apart for tet A, no differences in relative abundances of the other ARGs between FE and MPE were determined. These results suggest that the choice to not use antibiotics in broiler farming is not so effective to limit the ARGs spread in MPE and that further sources of ARGs should be considered including the preceding production phase with particular reference to the breeding stage.

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

“…Similar results were observed in the USA for the tet A gene in pastured “no antibiotic ever” poultry farms, showing a greater abundance than in cattle or sheep manure [ 29 ], and in Italy, where the environmental fecal samples recovered from a broiler antibiotic-free farm revealed a wide distribution of tet A [ 15 ].…”

“…A similar survey has already been performed in central Italy, involving only conventional broiler and turkey flocks, while a more extensive study was conducted in a high-density farming area of northern Italy, focusing on the microbial community and ARGs abundance in different types of conventional livestock manure (dairy cattle, poultry, and swine) [ 11 , 12 ]. More recently, a single antibiotic-free broiler farm, located in northern Italy, was investigated to quantify some representative ARGs at different sampling sites [ 15 ]. Finally, a metagenomic approach, with the aim to analyze the cecal resistome of broiler carcasses at the slaughterhouse, was performed by De Cesare et al [ 14 ].…”

“…In this respect, the increase in tetracycline genes amplified in T1 samples observed in both types of farming systems should be related to multiple sources of contamination of resistance determinants. Probably, the chickens were exposed to other extra-intestinal resistant bacteria during the cycle production, as already suggested [ 15 ].…”

“…However, this evidence disappeared when the corresponding carcasses were compared [ 14 ]. Conversely, Salerno et al [ 15 ] demonstrated that the abundance of ARGs harbored by the microbial community coming from broilers raised without antibiotics can be considered comparable to what has been reported in conventional farms.…”

Calves as Main Reservoir of Antibiotic Resistance Genes in Dairy Farms

“…The relative abundances of the tested ARGs were in the range of those generally found in other Italian animal farms ( 16 , 17 ) and farms sampled in other countries ( 18 , 19 ). This result highlights once more the need to improve knowledge about the role of the farms as hotspots of AR, threatening the farmworkers' ( 20 ) and environmental health ( 21 ) and, therefore, constituting a general concern for human health.…”