Macrolide resistance in animal streptococci

The increasing macrolide resistance (MR) in Streptococcus spp. causing human and animal infections in the last decades is a concern for global health. The objectives of this study were to analyse the MR rates of Streptococcus spp. from animals and their resistance determinants. We conducted a retrospective study of an animal streptococcus collection (307 isolates) from farm, wild animals and pets in Catalonia, Northeast Spain. Identification was done by MALDI-TOF and antimicrobial susceptibility to erythromycin and clindamycin was tested by disc diffusion (EUCAST). Selected isolates (n=50) were subjected to whole genome sequencing (WGS). Mobile genetic elements (MGEs), such as integrative and conjugative elements (ICEs) and integrative and mobilizable elements (IMEs), were identified using ICEscreen. Streptococcal strains were mainly isolated from domestic swine (50.5%) and wild boars (19.2%), with S. suis (54.4%) and S. hyovaginalis (14%) the predominant species. The MR phenotypes found were MLSB (n=145), M (n=6) and L (n=30). Macrolide (84.5%) and lincosamide (94.8%) resistance rates from swine strains were higher than those from other animals (13.2% and 18.4%, respectively, p<0.001). The predominant resistant genes found were erm(B) (n=38), tet(O) (n=29), vga(F) (n=20) and lnu(B)-lsa(E) (n=11) and were mostly associated to ICEs belonging to the Tn5252 family. Animal streptococci presented high MR rates, especially concerning swine strains, associated with a variety of resistance determinants. MGEs were the main carriers of resistance determinants and contributors of its spread.