Abstract

VIGLIAROLO, Laura et al. Sensibilidad a trimetoprima-sulfametoxazol de Streptococcus pyogenes aislados de infecciones invasivas. Medicina (B. Aires) [online]. 2018, vol.78, n.5, pp.311-314. ISSN 0025-7680.

It is erroneously believed that group A streptococci (GAS) are universally resistant to trimethoprim-sulfamethoxazole (TMS). This is mainly because media commonly used for in vitro determination of susceptibility to antibiotics contain thymidine, a nucleoside that antagonizes the antibiotic effect of TMS. The objective of this work was to determine EGA sensitivity to TMS in the presence and absence of thymidine. To this aim, 95 GAS isolates obtained from clinical tissues with i nvasive infections were analyzed. Susceptibility tests were performed by diffusion with TMS discs in Mueller Hinton agar supplemented either with 5% sheep blood or with 5% lysed equine blood (MH-LEB). Lysed equine blood contains thymidine phosphorylase, which degrades this nucleoside. Epsilometry (Etest) was used as gold standard. Quality controls with Enterococcus faecalis strain ATCC 29212 were satisfactory with both media. A 100% sensitivity to TMS was found in MH-SEL whereas 6 isolates (6.3%) resulted resistant in MH-SC; only one of them was found to have intermediate susceptibility by Etest (MIC > 1.5/28 μg/ml). The genetic determinants most frequently associated to TMS resistant EGA were not found in this isolate. Probably, if more accurate GAS-specific cut-off points were established for diffusion, the correlation with dilution methods or with the Etest could be improved, even employing MH-SB.

Keywords : Susceptibility; Trimethoprim-sulfamethoxazole; Streptococcus pyogenes.

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