Typing of Staphylococcus aureus strains isolated from milk cows with subclinical mastitis in Dakar, Senegal Kadja

Abstract

Surveys conducted in Senegal have shown a strong association of staphylococci with subclinical mastitis in dairy cows. This study aimed to characterise Staphylococcus aureus strains identified in the dairy farms in Dakar. Of a total of 244 Staphylococcus spp isolates col ected from 135 lactating cows with subclinical mastitis at six dairy herds in peri-urban region of Dakar, 109 S. aureus strains were isolated and identified using phenotypic methods. Using PCR, genes of thermonuclease and major capsular type 5 and 8 antigens were identified respectively in 98.17%, 93.58% and 1.84% of S. aureus strains. Similarly, the spa gene was found in 68.81% of S. aureus strains, luk D (62.39%) and luk S (0.92%). Among the virulence genes sought, spa, Luk S and Luk D genes were found respectively in 68.81%, 62.39% and 0.92% strains of S. aureus. However, the lukF, lukM and tst1 genes were absent in al isolated S. aureus. Among the six enterotoxins analysed, none of the S. aureus harboured the genes sea, sec and seh. Only the seb, sei and sej were found respectively at rates of 2.75%, 3.67% and 26.6%. Final y, the gene for resistance to methicil in was found in 2.75% of the strains isolated. The analysis of the association between virulence genes and the presence of subclinical mastitis showed the importance of genes Spa lukD and SEJ. Antibiotic resistance testing revealed a good sensitivity of S. aureus to most of the antibiotics tested. This study showed the low virulence of the S aureus strains isolated. Keywords: Dairy cows - Subclinical mastitis - Staphylococcus aureus - PCR - Dakar Des enquetes menees au Senegal ont montre la forte correlation des staphylocoques aux mammites subcliniques chez les vaches laitieres. La presente etude avait pour but de caracteriser les souches de Staphylococcus aureus identifies dans les fermes laitieres a Dakar. Sur un total de 244 isolats de Staphylococcus spp isoles de 135 vaches laitieres a mammites subcliniques dans six troupeaux de vaches laitieres en zone peri-urbaine de Dakar, 109 souches de S. aureus ontete isolees et identifiees par des methodes phenotypiques. Par PCR, les genes de la thermonuclease et des antigenes capsulaires majeurs 5 et 8 ont ete identifies respectivement chez 98,17%, 93.58% et 1,84% des souches de S. aureus. Parmi les genes de virulence recherches, les genes spa, Luk D et Luk S ont ete retrouves respectivement chez 68,81%, 62,39% et 0,92% des souches de S. aureus. En revanche, les genes lukF, lukM et tst1 etaient absents. Parmi les six enterotoxines recherchees, sec et seh etaient absentes, seb, sei et sej ont ete retrouvees respectivement chez 2,75%, 3,67% et de 26,6% des souches. Enfin, le gene de resistance a la methicil ine a ete retrouve dans 2,75% des souches isolees. L’analyse de l’association entre les genes de virulence et la presence de mammites subcliniques a montre l’importance des genes spa, lukD et sej. Une bonne sensibilite de S. aureus a ete notee a la plupart des antibiotiques testes. Cette etude a montre la faible virulence des souches de S. aureus isolees. Mots-cles: vaches laitieres - mammites subcliniques - S taphylococcus aureus - PCR - Dakar