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Escherichia coli is one of the major pathogens causing mastitis in lactating mammals. We hypothesized that E. coli from the gut and mammary glands may have similar genomic characteristics in the causation of mastitis. To test this hypothesis, we used whole genome sequencing to analyze two multidrug resistant E. coli strains isolated from mammary tissue (G2M6U) and fecal sample (G6M1F) of experimentally induced mastitis mice. Both strains showed resistance to multiple (>7) antibiotics such as oxacillin, aztreonam, nalidixic acid, streptomycin, gentamicin, cefoxitin, ampicillin, tetracycline, azithromycin and nitrofurantoin. The genome of E. coli G2M6U had 59 antimicrobial resistance genes (ARGs) and 159 virulence factor genes (VFGs), while the E. coli G6M1F genome possessed 77 ARGs and 178 VFGs. Both strains were found to be genetically related to many E. coli strains causing mastitis and enteric diseases originating from different hosts and regions. The G6M1F had several unique ARGs (e.g., Qnr S1, sul 2, tet A, tet R, emr K, bla TEM-1/105, and aph (6)-Id, aph (3″)-Ib) conferring resistance to certain antibiotics, whereas G2M6U had a unique heat-stable enterotoxin gene ( ast A) and 7192 single nucleotide polymorphisms. Furthermore, there were 43 and 111 unique genes identified in G2M6U and G6M1F genomes, respectively. These results indicate distinct differences in the genomic characteristics of E. coli strain G2M6U and G6M1F that might have important implications in the pathophysiology of mammalian mastitis, and treatment strategies for mastitis in dairy animals., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Klebsiella pneumoniae is one of the most important mastitis-causing pathogens. The multidrug-resistant K. pneumoniae strain MNH_G2C5F was isolated from the feces of a cow with clinical mastitis. The MNH_G2C5F strain had a genome size of 5,381,832 bp (85.0× coverage) and typed as sequence type 273 (ST273)., Competing Interests: The authors declare no conflict of interest.

We sequenced the genome of Staphylococcus warneri G1M1F, a multidrug-resistant strain isolated from fecal samples of mice with induced mastitis. The complete genome of G1M1F consists of one chromosome of 2,504,515 bp and two plasmid replicons of 28,679 and 8,615 bp; it comprises 32.7% GC content, with 60× genome coverage., Competing Interests: The authors declare no conflict of interest.

Klebsiella pneumoniae is one of the most common and important mastitis-causing bacteria, and strain MNH_G2C5 was isolated from the milk of a cow suffering from clinical mastitis in a dairy farm of the Gazipur district of Bangladesh. The MNH_G2C5 genome was estimated to be 4,589,728 bp, with 65.5% genome coverage., Competing Interests: The authors declare no conflict of interest.