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

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

CABA

Congreso; XV Congreso Argentino de Microbiología; 2019

Introduction and objectives: Characterization 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 and 6% to the Nichols-like group, with up to 100% macrolide resistance. Argentina has a higher frequency of Nichols-like strains (27%) and low macrolide resistance (14%). Since several studies suggested that the molecular epidemiology of TPA is changing, our objective was to assess TPA strain distribution and macrolide resistance in Buenos Aires. Materials and methods: DNA was isolated from swabs from syphilis patients in 2018. TPA loci TP0136, TP0548, 23SrDNA were characterized by Sequencing-Based Molecular Typing. 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. Results: A 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). Conclusions: The 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.