Low-Level Tetracycline Resistance Gene _3 in .

(.) spp. are the most important foodborne, bacterial, and zoonotic pathogens worldwide. Resistance monitoring of foodborne bacterial pathogens is an important tool to control antimicrobial resistance as a part of the "One Health" approach. The detection and functionality of new resistance genes are of paramount importance in applying more effective screening methods based on whole genome sequencing (WGS). Most tetracycline-resistant spp. isolates harbor , a gene that encodes a ribosomal protection protein. Here we describe _3, which has been identified in two food isolates of and is very similar to the gene in , having a truncated promoter sequence. This gene confers resistance to tetracycline below 1 mg/L, which is the epidemiological cut-off value. We have analyzed the entire genome of these two isolates, together with a isolate found to have high-level resistance to tetracycline. In contrast to the highly resistant isolate, the promoter of _3 is highly responsive to tetracycline, as observed by reverse transcription polymerase chain reaction (RT-PCR). In addition, the two isolates possess a CRISPR repeat, fluoroquinolone resistance due to the point mutation C257T, a β-lactamase resistance gene , a multidrug efflux pump CmeABC and its repressor CmeR, but no plasmid. Low-level antibiotic resistant might therefore have an advantage for surviving in non-host environments.