Dramatic increase of macrolide resistance in Treponema pallidum isolates in Argentina.

MORANDO N; VRBOVA E; MELGAR A; RABINOVICH D; SMAJS D; PANDO MA

Montreal

Conferencia; 23rd International AIDS Conference (AIDS 2020: Virtual); 2020

IAS

Background: Globally, approximately 94% of Treponema pallidum (TPA) clinical isolates belong to the SS14-like group, 6% belong to the Nichols-like group and macrolide resistance ranges from 0 to 100%. A previous study revealed that Argentina has a different distribution pattern with a higher frequency of Nichols-like strains (27%) and low levels of macrolide resistance (14%). Several studies suggested that the molecular epidemiology of TPA is changing, so our goal was to update the information on circulating TPA strains in order to assess strain distribution and macrolide resistance frequency in Buenos Aires. Methods: Swab samples from patients with clinical symptoms of syphilis were collected during 2015-2018. DNA was isolated and three loci (TP0136, TP0548, 23S rRNA) were characterized by sequencing-based typing. Strains were classified into two clades based on similarity to reference sequences: Nichols-like and SS14-like. We determined the presence of macrolide resistance-associated mutations (A2058G, A2059G) by examination of the 23S rRNA gene sequence. The distribution of allelic profiles was based on combinations of TP0136, TP0548 and 23S rRNA sequences. Analyses were performed using Fisher´s exact test (IBM SPSS Statistics Base 22.0). Results: Among 32 swab samples 40.6% were classified as Nichols-like and 59.4% as SS14-like. Macrolide resistance prevalence was found to be 51.7%, being significantly more frequent among SS14-like samples as compared with Nichols-like samples (70.6% (12/17) vs. 23.1% (3/12), respectively; p=0.0253). Nine distinct allelic profiles were found, four related to the SS14 strain and five related to the Nichols strain. Compared to a previously published study (samples collected in the same setting between 2006-2013, n=41), macrolide resistance significantly increased (51.7% vs. 14.3%, p=0.0012) between the studies. The frequency of Nichols-like strains increased (26.8% vs. 40.6%, p=0.31), but not with statistical significance. Discussion: Even though macrolide resistance isolates were previously detected at a relatively low frequency in Argentina, our results reveal a dramatic increase. Our results are in agreement with international tendencies and underscore the need to pursue further TPA molecular typing studies in Argentina and Latin America.