Investigation of molecular mechanisms underlying tetracycline resistance in thermophilic spp. suggests that previous reports of (A)-mediated resistance in these bacteria are premature.

The true prevalence of (A), which codes for a tetracycline efflux pump, in thermophilic spp. requires clarification after reports emerged in Iran (2014) and Kenya (2016) of the novel detection of (A) in . During our investigation of antibiotic resistance mechanisms in a sample of Irish thermophilic broiler isolates, it was determined that 100% of tetracycline-resistant isolates (n = 119) harboured (O). Accessory tetracycline-resistance mechanisms were considered as tetracycline minimum inhibitory concentrations ranged from 4 to ≥ 64 mg/L. Primers previously reported for the detection of (A) in failed to produce an amplicon using a positive control strain ( K12 SK1592 containing the pBR322 plasmid) and a selection of isolates. Accordingly, we designed new (A)-targeting primers on SnapGene2.3.2 that successfully generated a 407 bp product from the positive control strain only. Further in silico analysis using BLASTn and SnapGene2.3.2 revealed that previously reported (A) sequences deposited on GenBank shared 100% homology with (O). We postulate that this gave rise to the erroneous report of a high prevalence among a pool of Kenyan broiler isolates that were tested using primers designed based on these apparent (A) sequences. In conclusion, further work would be required to determine whether the homology between (A) potentially present in and known (A) genes would be sufficient to allow amplification using the primers designed in our study. Finally, the existence of (A) in thermophilic spp. remains to be demonstrated.