Bovine mastitis associated with Enterobacteriaceae in Brazil: a systematic review

Bovine mastitis caused by Enterobacteriaceae represents an important sanitary and economic challenge in dairy production systems. This systematic review aimed to synthesize the reported prevalence of Enterobacteriaceae isolated from bovine mastitis cases in Brazil and to describe the main epidemiological, diagnostic, and antimicrobial resistance characteristics reported in the literature. The search was conducted in January 2025 across PubMed, Scopus, Web of Science, ScienceDirect, Springer, BVS, Scielo, and Google Scholar, following PRISMA guidelines. Studies conducted in Brazil, published in Portuguese or English, and reporting primary data on Enterobacteriaceae associated with bovine mastitis were included. Screening, data extraction, and methodological quality assessment using the JBI checklist for prevalence studies were performed independently by two reviewers. Eighty studies published between 1985 and 2024 met the eligibility criteria. The included studies encompassed at least 70,815 mammary quarter samples and 43,068 dairy cows. Research was geographically concentrated in the South and Southeast regions. Studies focusing exclusively on clinical mastitis reported higher prevalence ranges compared to those evaluating subclinical cases. Escherichia coli was the most frequently reported species, followed by Klebsiella spp. and Enterobacter spp. Diagnostic approaches evolved over time, with increasing use of molecular methods and MALDI-TOF after 2010. Only a small proportion of studies reported antimicrobial resistance data. The marked methodological heterogeneity and regional concentration of studies limit national comparability and preclude pooled prevalence estimation. Nonetheless, the evidence consistently indicates that Enterobacteriaceae , particularly E. coli , are frequently reported among mastitis etiological agents in Brazilian dairy herds. Standardized reporting and broader regional surveillance, including systematic AMR assessment, are needed to improve epidemiological interpretation and support mastitis control strategies. • Enterobacteriaceae are relevant environmental pathogens in bovine mastitis in Brazil. • Escherichia coli is the most frequently reported Enterobacteriaceae species. • Klebsiella and Enterobacter show lower but epidemiologically relevant occurrence. • Enterobacteriaceae are detected in both clinical and subclinical mastitis cases. • Antimicrobial resistance data on Enterobacteriaceae mastitis in Brazil remain scarce.