High frequency of Nichols-like strains and high macrolide resistance in Treponema pallidum isolates in Argentina

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

Buenos Aires

Congreso; XV Congreso Argentino de Microbiología. Asociación Argentina de Microbiología; 2019

AAM

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 using the QIAamp DNA minikit (Quiagen, Hilden, Germany). TPA TP0105 and TP0319 genes were amplified by nested PCR in order to detect positive samples. Among PCR positive samples, 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: A total of 32 swab samples were typable (27 completely and five partially typed). Of these, 40.6% (n=13) were classified as Nichols-like and 59.4% (n=19) as SS14-like. Macrolide resistance prevalence was found to be 51.7% (15/29). Macrolide resistance was 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). A total of 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), the frequency of Nichols-like strains increased (26.8% vs. 40.6%, p=0.31), but not with statistical significance; however, macrolide resistance significantly increased (51.7% vs. 14.3%, p=0.0012) between the studies. Discussion: Consistently with the previous report, Nichols-like TPA strain are more prevalent in Argentina than in most countries. 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.