Occurrence and distribution of antibiotic resistance genes in Elymus nutans silage from different altitudes of the Qinghai-Tibetan Plateau

Xia Zhang^1,2Dongmei Xu²Rina Su²Fuhou Li³Hu Chen^2,4Mengya Jia²Mengyan Chen²X. S. Guo^1,2*

• ¹Lanzhou University, Lanzhou, China
• ²School of Life Sciences, Lanzhou University, Lanzhou, Gansu Province, China
• ³School of Life Science and Engineering, Lanzhou University of Technology, Lanzhou, Gansu Province, China
• ⁴Institute of Evidence-Based Medicine, School of Basic Medical Sciences, Lanzhou University, Lanzhou, Gansu Province, China

Antibiotic resistance genes (ARGs) and antibiotic-resistant bacteria (ARB) have attracted more attentions in fermented feed recently. However, little information is available on the occurrence and distribution of ARGs in ensiled forages in the alpine region of the Qinghai-Tibetan plateau (QTP) with an extremely harsh environment. Hence, the study investigated the distribution and spread mechanism of ARB and ARGs in Elymus nutans silage along 2600 m (low), 3600 m (medium) and 4600 m (high) altitude in the QTP. The major ARG types in Elymus nutans silage were multidrug, aminoglycoside, bacitracin, beta-lactam and polymyxin, while tnpA and IS91 were the dominant mobile genetic elements (MGEs) subtypes in the Elymus nutans silage. The dominant ARGs were mainly carried by Pantoea, Enterobacter, Serratia, and Lelliottia. Although altitudinal gradient had no influence on the diversity or abundance of other ARGs and MGEs in the Elymus nutans silage (P > 0.05), the network co-occurrence patterns among ARGs, MGEs, and bacteria in high-altitude silage were more complex than that in low-and medium-altitude silages. The dominant clinical ARGs in the alpine silage were bacA and acrF, and the abundance of clinical ARGs decreased with prolonged fermentation time. This study provides important data on the status of ARGs in ensiled forage from the alpine region of the QTP.