Non-aureus staphylococci in fecal samples of dairy cows: First report and phenotypic and genotypic characterization

摘要

The aims of this study were to determine whethernon-aureus staphylococci (NAS) are present in rectalfeces of healthy dairy cows, and if so, to delineatespecies to which they belong and to study severalphenotypic and genotypic traits as a first step towarddetermining the potential impact of fecal sheddingof NAS on bovine udder health. Fecal samples wereaseptically collected from the rectum of 25 randomlyselected clinically healthy dairy cows in a commercialdairy herd using an automated milking system. FecalNAS were isolated and then identified at the specieslevel using transfer RNA-intergenic spacer PCR andsequencing of the 16S rRNA housekeeping gene. Straintyping was performed using random amplification ofpolymorphic DNA (RAPD)-PCR. The antimicrobialresistance profiles, biofilm formation, and growth andinhibitory characteristics of all NAS isolates were evaluated.Half of the cows were shedding NAS, resulting in31 NAS isolates belonging to 11 different species. Themost prevalent species were Staphylococcus rostri (23%,n = 7), Staphylococcus cohnii (16%, n = 5), and Staphylococcushaemolyticus (13%, n = 4) with all Staphylococcusagnetis, Staphylococcus chromogenes, and Staph.rostri isolates belonging to the same strain accordingto RAPD banding patterns. Acquired antimicrobialresistance was observed in 28 of the 31 NAS isolates,mainly due to β-lactamase production. Most of theisolates (84%, n = 27) had a weak biofilm-forming potential,but only 2 contained the bap gene. The ica andaap genes were not detected in any of the isolates. Invitro growth of Staphylococcus aureus and Streptococcusdysgalactiae was inhibited by Staph. agnetis isolates,and Staph. chromogenes isolates were able to inhibit thegrowth of Strep. dysgalactiae and Streptococcus uberis.All fecal isolates were able to grow when oxygen andiron were limitedly available, mimicking the growthconditions in the mammary gland.