Genômica comparativa de staphylococcus aureus isolados de mastite em ruminantes

Abstract

Mastitis is an infection of the mammary gland that affects ruminants and can affect the quantity and quality of milk from the affected animal, which when ingested can cause food poisoning in humans. The primary pathogen responsible for cases of mastitis in production animals are Staphylococcus spp. The genus is divided into two groups, based on the ability to coagulate plasma or blood. Coagulase positive Staphylococcus (CoPS) occurs mostly in the S. aureus species. Coagulase negative Staphylococcus (CoNS) are the other species of staphylococci. CoPS are the most damaging for the herd and CoNS are considered emerging pathogens and have been causing serious damage to the quality of milk. Identifying coagulase-negative S. aureus is considered an atypical event in clinical diagnosis. The erroneous characterization of the species as S. non-aureus if coagulation does not occur. S. aureus is both a commensal and pathogenic bacterium; it is considered the primary aetiology of mastitis in ruminants, presenting a problematic cure, possible recurrence, and compromising the economy and public health worldwide. This thesis was done with the purpose of sequencing and analyzing genomes of S. aureus isolated from mastitis in ovine and bovine from France and Brazil. The thesis is composed of two papers, the first analyzes the specificity, evolutionary relationship and characteristics that may be associated with the pathogenicity of S. aureus isolated from mastitis in ovine. In general, ovine genomes show a high niche-host similarity and can be classified at the molecular typing and phylogeny level, unlike sequences from cattle and humans. The second article analyzes at genomic level samples isolated from bovine mastitis in Brazil, identified in vitro by coagulase test and MALDI-TOF MS as coagulase-negative S. aureus, aiming to identify particularities involving these samples and sequences of coagulase-positive S. aureus. Two samples previously identified as coagulase-negative S. aureus were classified as S. capiti. The result that stood out the most was the behaviour of the gene responsible for the expression of the von Willebrand factor-binding protein (vWbp), besides the enzyme coagulase, which is also essential in the coagulation process. In the vWbp alignment, fragmentation was identified only in the sequences referring to the coagulase-negative S. aureus samples; this may be related to the absence of coagulation in these samples. The results generate new knowledge about the genomic architecture associated with the zoonotic risk of S. aureus. Furthermore, this work can be considered one of the first genomic studies for coagulase-negative S. aureus isolated from mastitis in bovine, opening the way for new studies to classify the genus of Staphylococcus.