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

INTRODUCTION

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.

METHODS

The study investigated the distribution and spread mechanism of ARB and ARGs in silage along 2600 m (low), 3600 m (medium) and 4600 m (high) altitude in the QTP.

RESULTS

The major ARG types in silage were multidrug, aminoglycoside, bacitracin, beta-lactam and polymyxin, while tnpA and IS91 were the dominant mobile genetic elements (MGEs) subtypes in the silage. The dominant ARGs were mainly carried by . Although altitudinal gradient had no influence on the diversity or abundance of other ARGs and MGEs in the silage ( > 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.

DISCUSSION

This study provides important data on the status of ARGs in ensiled forage from the alpine region of the QTP.