CONICET | Buscador de Institutos y Recursos Humanos

Staphylococcus aureus can act as a major pathogens in many animal species, and it represents one of the leading causes of mastitis both in lactating cows and periparturient dairy heifers. There have been reported different infection severity associated with this pathogen, but the mechanisms leading to these different infections are not yet fully understood. In this work, we analyzed 4 different strains of S. aureus, isolated from cattle, using whole genome sequencing. Two of them, named 5011 and 5128, were isolated from lactating cows in Santa Fe province and caused chronic infections. The sample 117 was isolated from a lactating cow in Córdoba province and caused a clinic infection. Lastly, the sample B456 was isolated from a heifer in Santa Fe. Using PCR, the capsule of three of them, 5128, 117 and B456, was classified as type 5, while 5011 remained unclassified. The 4 strains were sequenced using Illumina MiSeq, generating 2x250bp reads. In addition, the samples 5128 and 5011 were also sequenced using MinION technology (Oxford Nanopore). By combining sequencing technologies, we manage to circularize the genome and all plasmids of samples 5128 and 5011. The assembly of samples 117 and b456 resulted in 34 and 89 contigs respectively. An in silico MLST analysis showed that only two strains shared the same ST, 5128 and 117. Finally, in average, 2500 genes were predicted for each strain, from which 2121 were strictly conserved across all them (>=99% nucleotide identity). Among the unique genes, resistance to different antibiotics, virulence factors and capsular polysaccharide biosynthesis proteins were found and compared. In conclusion, we were able to reconstruct the complete genome of 4 strains of S. aureus showing different disease patterns. The study and comparison of these genomes would help to explain the differences between the disease patterns and to identify new targets for the development of new mastitis vaccines.

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