High frequency of Nichols-like strains and rising prevalence of macrolide resistance in T. pallidum isolates in Argentina.

VRBOVÁ, ELISKA; MAJS, DAVID; GUZMAN, LUCÍA FLORENCIA; RABINOVICH, DANIEL; MORANDO, NICOLÁS; MELGAR, ASUNTA; PANDO, MARÍA DE LOS ÁNGELES

Vancouver

Congreso; STI & HVI 2019 World Congress; 2019

BackgroundCharacterization of Treponema pallidum (TPA) clinical isolates at the genomic level helps to better describe the epidemic conditions and elucidate transmission networks. Globally, 94% of clinical isolates belong to the SS14-like group, 6% to the Nichols-like group, with up to 100% macrolide resistance.Argentina has higher frequency of Nichols-like strains (27%) and low macrolide resistance (14%). Since several studies suggested that the molecular epidemiology of T. pallidum is changing, our objective was to assess Treponema pallidum strain distribution and macrolide resistance in Buenos Aires.MethodsDNA was isolated from swabs from syphilis patients in 2018. TPA loci TP0136, TP0548, 23SrDNA were characterized by SBMT. Strains were classified into clades Nichols-like or SS14-like. We determined the presence of macrolide resistance-associated mutations (A2058G/A2059G) in 23SrDNA. Analyses were performed using Fisher´s exact test.ResultsA total of 32 swab samples were typeable: 40.6% (n=13) were Nichols-like and 59.4% (n=19) SS14-like. Macrolide resistance prevalence was 46.9% (15/32), with SS14-like samples being significantly more frequent than Nichols-like samples (63.2% (12/19) vs. 23.1% (3/13), respectively; p=0.0359). A total of 6 allelic profiles were found, 1 different from genotypes described previously. Unlike a previous study (samples collected in the same setting between 2006-2013, n=41), the frequency of Nichols-like strains tended to increase (26.8% vs. 40.6%,p=0.31). Overall, macrolide resistance increased significantly (14.3% vs. 46.9%, p=0.0037) between studies. Specifically, resistance significantly increased in SS14-like samples (16.7% vs. 63.2%, p=0.0017) but not in Nichols-like samples (9.1% vs. 23.1%, p=0.5963).ConclusionThe frequency of Nichols-like strains in Argentina is considerably higher than that reported in most countries. Even though macrolide resistant isolates were detected previously at a relatively low frequency in Argentina, our results reveal a dramatic increase. These results are in line with international tendencies.