This study first reports novel antimicrobial resistance phenotypes of Serratia marcescens in bovine mastitis, including resistance to Tobramycin, Cefuroxime, Colistin, and Nitrofurantoin. Whole-genome sequencing identifies multiple resistance and virulence genes, while phylogenetic analysis demonstrates high genetic similarity between these isolates and environmental Serratia marcescens strains, suggesting environmental transmission as a potential source of multidrug-resistant pathogens in dairy farms.
Literature Overview
This article, 'Serratia marcescens Isolates from Bovine Mastitic Milk: Antimicrobial Resistance and Virulence Features', published in the journal Antibiotics, systematically reviews the antimicrobial resistance and virulence features of Serratia marcescens in bovine mastitis. Phenotypic and genotypic analyses reveal resistance to multiple β-lactam, aminoglycoside, cephalosporin, and nitrofuran antibiotics. Whole-genome sequencing identifies key resistance and virulence genes, while phylogenetic analysis indicates closer genetic proximity to environmental rather than human clinical strains of Serratia marcescens.
Background Knowledge
Bovine mastitis (BM) is among the most economically significant diseases in dairy farming, primarily caused by Gram-negative bacteria such as E. coli, Klebsiella, and increasingly Serratia marcescens. As an opportunistic pathogen widely present in the environment and hospital-acquired infections, Serratia marcescens has not been fully characterized in BM at the molecular level. Rising antibiotic treatment failures are attributed to evolved resistance mechanisms including efflux pumps, enzymatic inactivation, and target modification. Virulence factors like motility-related proteins (FlgH, FliP, FliM, FliG) play critical roles in infection and biofilm formation. This study provides the first genomic characterization of Serratia marcescens in BM, offering novel genetic targets for precision prevention and control strategies.
Research Methods and Experiments
Four Gram-negative isolates (1-DH1, 2-DH1, 3-DH2, 4-DH3) from three Portuguese dairy farms were analyzed, with three strains undergoing whole-genome sequencing (WGS). Phenotypic identification and antimicrobial susceptibility testing (AST) employed Neg-Urine-Combo98 panels on the MicroScan WalkAway Plus system. Genomic comparisons used Mash and Panaroo for phylogenetic analysis. Resistance (AMR) and virulence factor (VF) genes were screened against CARD, ResFinder, NCBI, and VFDB databases using ABRicate BLAST pipelines. Genome assembly and polishing used Flye and Medaka, with CheckM validating genomic completeness.
Key Conclusions and Perspectives
Research Significance and Prospects
This work establishes the first phylogenetic link between bovine mastitis-associated Serratia marcescens and environmental strains, offering an ecological perspective for AMR control. Future studies should explore gene expression regulation and horizontal gene transfer events to identify transmission routes. The findings support whole-genome sequencing as a superior diagnostic tool over traditional phenotypic methods, providing genomic evidence for precision veterinary medicine and One Health approaches in dairy farming.
Conclusion
This study provides the first systematic characterization of antimicrobial resistance and virulence factors in Serratia marcescens associated with bovine mastitis, emphasizing the environmental origin of these pathogens. Dual phenotypic and genomic analyses reveal evolved resistance mechanisms, indicating potential limitations of conventional antibiotics (Tobramycin, Cefuroxime, Colistin, Nitrofurantoin) against this pathogen. Phylogenetic proximity to environmental strains offers important ecological-genetic clues for implementing farm-level infection control and AMR surveillance programs. These findings have significant implications for optimizing mastitis treatment protocols, preventing resistance dissemination, and advancing One Health strategies in dairy production systems.
