Clinical and Epidemiological Landscape of Antimicrobial Resistance and Virulence in Streptococcus Species

Species of the genus Streptococcus constitute important pathogens in human and veterinary medicine, being responsible for a wide spectrum of infections ranging from mild illnesses to severe invasive pathologies. Although β-lactams continue to be effective against most species, the global increase in resistance to macrolides, lincosamides, tetracyclines, and, in some cases, reduced susceptibility to penicillin represents a growing challenge for antimicrobial therapy. This review synthesizes the clinical and epidemiological landscape of antimicrobial resistance in the main Streptococcus species, including Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, Streptococcus dysgalactiae, and other species of clinical and veterinary relevance, addressing their epidemiological profiles, molecular mechanisms of resistance, and virulence factors. The main genetic determinants involved in resistance are discussed, namely the erm, mef, and tet genes, as well as the impact of alterations in penicillin-binding proteins, horizontal gene transfer, and biofilm formation on the persistence of infections and decreased therapeutic efficacy. Simultaneously, the main virulence factors are analyzed, including polysaccharide capsules, adhesins, toxins, extracellular enzymes, and immune response evasion mechanisms that contribute to the colonization, dissemination, and severity of infections. The importance of epidemiological and genomic surveillance, particularly through whole-genome sequencing, in monitoring the spread of resistant clones and identifying determinants of resistance and virulence is also highlighted. Taken together, the data highlight the need to strengthen programs for the rational use of antimicrobials, to promote integrated surveillance strategies from a One Health perspective, and to deepen knowledge about the interaction between antimicrobial resistance and virulence, in order to improve strategies for the prevention, diagnosis, and treatment of infections caused by Streptococcus spp.