[National surveillance of clinical isolates of resistant to linezolid carrying the optrA gene in Colombia, 2014-2019].

Objective: To describe the epidemiological, phenotypical and genetic characteristics of clinical isolates carrying the gene identified in antimicrobial resistance surveillance by the laboratory of the National Institute of Health of Colombia.

Methods: Between October 2014 and February 2019, 25 isolates of spp. resistant to linezolid were received. Antimicrobial identification and sensitivity were determined using Vitek 2 and the minimum inhibitory concentration (MIC) to linezolid was established with E-test. The gene was detected by PCR, and the genetic diversity of -positive isolates was tested with Diversilab. Six isolates were selected to perform whole genome sequencing.

Results: The gene was confirmed in 23/25 isolates of from seven departments in Colombia. The isolates presented a MIC to linezolid between 8 and >256µg/mL. Typing by Diversilab showed a wide genetic variability. All the isolates analyzed by whole genome sequencing showed the resistance genes , , , , and in addition to and were negative for other mechanisms of resistance to linezolid. Three type sequences and three variants were identified: ST16 (2), ST476 () and ST618 (). The genetic environment of the (ST16) isolates presented the impB, fex, optrA segment, associated with plasmid, while in two isolates ( and ) the transferable chromosomal element Tn6674-like was found.

Conclusion: -positive clinical isolates present a high genetic diversity, with different clones and variants related to two types of structures and different mobile genetic elements.