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Molecular characterization of Staphylococcus aureus and Streptococcus uberis isolates of intramammary infections of dairy cows

Alves, Bruna Gomes

Biblioteca Digital de Teses e Dissertações da USP; Universidade de São Paulo; Faculdade de Medicina Veterinária e Zootecnia 2020-06-19

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  • Título:
    Molecular characterization of Staphylococcus aureus and Streptococcus uberis isolates of intramammary infections of dairy cows
  • Autor: Alves, Bruna Gomes
  • Orientador: Santos, Marcos Veiga dos
  • Assuntos: Staphylococcus Aureus; Genotipagem; Dot Blot; Concentração Inibitória Mínima; Streptococcus Uberis; Genotyping; Minimal Inhibitory Concentration; Staphylococci; Streptococci
  • Notas: Tese (Doutorado)
  • Descrição: The bovine mastitis is the disease more frequent of dairy cows, which results in significant economic losses. Staphyloccoccus aureus and Streptococcus uberis are among the main causes of clinical (CM) and subclinical (MSC) mastitis, because they are difficult to control by conventional measures, since both have mechanisms of immune system evasion, adherence and internalization in the mammary tissues. Therefore, this thesis was organized in three experiments: 1) Genotypic characterization of S. aureus isolated from mastitis from Brazilian herds and from other countries; 2) Genotypic characterization and antimicrobial sensitivity of S. aureus isolates identified before and after treatment of MSC during lactation; and 3) Genotypic diversity and virulence factors of S. uberis isolated from intramammary infections of dairy cows in Brazil. In experiment 1, 70 S. aureus isolates (35 from MC and 35 from MSC) were identified in milk samples from cows\' mammary quarters in 16 herds in Brazil. After the selection, 15 Brazilian isolates were grouped with isolates from Argentina (n=16), Colombia (n=15), Germany (n=17), Italy (n=17), USA (n=17), South Africa (n=11) and Tunisia (n=12) for genotyping by RS-PCR, based on the amplification of the 16S-23S rRNA intergenic space and investigated in relation to 26 virulence factors. In experiment 2, 79 S. aureus isolates were genotyped by pulsed-field gel electrophoresis (PFGE) and evaluated by minimum inhibitory concentration (MIC) to assess antimicrobial resitance profiles. In experiment 3, 44 isolates of S. uberis were evaluated by DNA hybridization using the dot blot methodology, to determine the genotypic diversity. The results of experiment 1 indicated high genotypic variability of S. aureus according to the countries evaluated, and high prevalence of genes related to invasion to the host organism (clfA, cna, fmtB and leucocidins). In addition, it was shown that the genotype pattern os S. aureus isolates were specific to each country, suggesting that control strategies should be formulated according to the region in question and the virulence of the strains involved in the infection. In experiment 2, a high similarity was identified between the isolates of the same herd, indicating genotypic specificity within the same region, even after treatments during lactation. In addition, all the isolates evaluated were susceptible to gentamicin, enrofloxacin, ciprofloxacin and tetracycline, although high resistance to amoxicillin and cephalexin has also been observed. In experiment 3, nine dot blot patterns were observed, indicating high heterogeneity of S. uberis isolates. It was possible to observe a high prevalence of genes regulating virulence factors, such as sua and gapC, responsible for the adherence and internalization of S. uberis in the mammary gland tissues. Thus, after the conclusion of the three studies, it was possible to conclude that there is a high genotypic diversity in S. aureus and S. uberis isolated from bovine intramammary infections in Brazil. In addition, it has been confirmed that these two species have numerous virulence factors that contribute to their permanence in the mammary gland and a limit control based on conventional measures. However, these control measures, such as the use of post-dipping, registration and monitoring of clinical cases and the culling chronic cows must be part of the bovine mastitis prevention plan, in order to reduce the severity and dispersion of cases. Molecular techniques are efficient in the identification and genetic characterization of bacterial isolates and can be auxiliary tools in the diagnosis and epidemiology of mastitis, guiding the control and treatment strategies of the disease.
  • DOI: 10.11606/T.10.2020.tde-07072020-081113
  • Editor: Biblioteca Digital de Teses e Dissertações da USP; Universidade de São Paulo; Faculdade de Medicina Veterinária e Zootecnia
  • Data de criação/publicação: 2020-06-19
  • Formato: Adobe PDF
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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