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<p>This study assessed the occurrence of <i>Streptococcus</i> spp. in milk samples from cows with visible clinical mastitis signs and from cows with high (≥ 200,000 cells/mL) or low (&lt; 200,000 cells/mL) somatic cell counts (SCC) across five Brazilian regions. Antimicrobial resistance and virulence-associated genes were investigated using phenotypic assays and whole-genome sequencing (WGS). Among 1,447 milk samples, <i>Streptococcus agalactiae</i> was the predominant species, followed by <i>Streptococcus uberis</i> and <i>Streptococcus dysgalactiae</i>, with most isolates associated with high SCC samples. Positive samples presented elevated SCC values, reinforcing the association between <i>Streptococcus</i> spp. and udder inflammation. High resistance rates to streptomycin and tetracycline were observed, and multidrug resistance was detected in one-third of the isolates. Genomic analysis of <i>S. agalactiae</i> identified two sequence types (ST-67 and ST-103), resistance genes associated with aminoglycoside, tetracycline, and macrolide resistance, and a broad repertoire of virulence-related genes. <i>S. agalactiae</i> isolates were detected exclusively in samples from Paraíba, whereas <i>S. uberis</i> was identified across all evaluated regions, suggesting distinct epidemiological patterns among <i>Streptococcus</i> species. Overall, these findings highlight the epidemiological relevance, antimicrobial resistance potential, and virulence-associated characteristics of <i>Streptococcus</i> spp. involved in bovine mastitis in Brazil, reinforcing the importance of continuous surveillance and improved mastitis control strategies in dairy herds.</p>

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Incidence of Streptococcus spp. and whole genome sequencing of Streptococcus agalactiae isolated from cow’s milk samples in Brazil

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月15日

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  • Rafaela Martins Morasi,
  • Bruna Lourenço Crippa,
  • Clarice Gebara,
  • Hélio Langoni,
  • Carlos Henrique Camargo,
  • Luiz Gustavo de Matos,
  • André Thaler Neto,
  • Mônica Correia Gonçalves,
  • Nathália Cristina Cirone-Silva

摘要

This study assessed the occurrence of Streptococcus spp. in milk samples from cows with visible clinical mastitis signs and from cows with high (≥ 200,000 cells/mL) or low (< 200,000 cells/mL) somatic cell counts (SCC) across five Brazilian regions. Antimicrobial resistance and virulence-associated genes were investigated using phenotypic assays and whole-genome sequencing (WGS). Among 1,447 milk samples, Streptococcus agalactiae was the predominant species, followed by Streptococcus uberis and Streptococcus dysgalactiae, with most isolates associated with high SCC samples. Positive samples presented elevated SCC values, reinforcing the association between Streptococcus spp. and udder inflammation. High resistance rates to streptomycin and tetracycline were observed, and multidrug resistance was detected in one-third of the isolates. Genomic analysis of S. agalactiae identified two sequence types (ST-67 and ST-103), resistance genes associated with aminoglycoside, tetracycline, and macrolide resistance, and a broad repertoire of virulence-related genes. S. agalactiae isolates were detected exclusively in samples from Paraíba, whereas S. uberis was identified across all evaluated regions, suggesting distinct epidemiological patterns among Streptococcus species. Overall, these findings highlight the epidemiological relevance, antimicrobial resistance potential, and virulence-associated characteristics of Streptococcus spp. involved in bovine mastitis in Brazil, reinforcing the importance of continuous surveillance and improved mastitis control strategies in dairy herds.