Abstract
ABSTRACT: This research aimed to investigate the genotypic relatedness of 18 Staphylococcus aureus strains isolated from intramammary infections in primiparous cows and extramammary sites on five dairy herds by rep-PCR using RW3A primers, and by PFGE using the endonuclease SmaI. The isolates were also evaluated in vitro for the susceptibility against beta-lactam antimicrobials drugs (penicillin and oxacillin), considering that beta-lactams are frequently used for treating staphylococcal intrammamary infections. The rep-PCR typing was highly discriminatory (D value= 0.9804) and a total of 15 patterns were detected. The PFGE method was also highly discriminatory (D value= 0.9667) and a total of 13 patterns were observed. A total of 15 out of 18 (83%) isolates were resistant to penicillin and one out of 18 (6%) to oxacillin. In conclusion, these findings confirmed the occurrence of a high genetic diversity of S. aureus strains at the herds and the presence of clonally-related strains only at the same herd, emphasizing a variety of genotypic profiles among the isolates.
Highlights
Primiparous dairy cows are of key significance for every dairy herd as their mammary gland health status will directly impact the longevity of the animals and herd productivity
All 18 isolates were confirmed to be S. aureus by Polymerase Chain Reaction (PCR) for nuc gene and the presence of the blaZ gene was detected in 100% (18/18) of them; mecA and mecC were not detected among the isolates
Considering the antimicrobial susceptibility testing results, approximately 83% (15/18) of the strains were resistant to penicillin and 6% (1/18) to oxacillin
Summary
Primiparous dairy cows are of key significance for every dairy herd as their mammary gland health status will directly impact the longevity of the animals and herd productivity. Despite of the common sense that they are not susceptible to intramammary infections (IMIs), an increasing number of recent studies have reported cases of mastitis in primiparous cows, mainly attributed to Staphylococcus spp. There are still a lot of uncertainties about the epidemiology of these IMIs and Staphylococcus aureus has been considered an important contagious agent transmitted among lactating animals (BAŞTAN et al, 2015). Previous researches suggest humans and environment as potential sources of S. aureus causing mastitis in dairy heifers (STALDER et al, 2014; BAŞTAN et al, 2015). Emerging antimicrobial resistance in S. aureus has posed a serious problem to the treatment of mastitis in dairy herds (DIAS et al, 2015). Considering the important role of Staphylococcus aureus on the mastitis etiology
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