Abstract
Aerococcus viridans is a wide spread bacterium in the environment and clinically this organism is associated with different diseases in animals and humans. However, the geno- and phenotypic characterization of A. viridans associated with bovine mastitis has not yet been reported. The objectives of this study were to investigate the genetic and phenotypic diversity of A. viridans isolates using three different molecular methods including 16S rRNA gene sequencing, pulsed-field gel electrophoresis and random amplified polymorphic DNA (RAPD) along with biochemical tests, including antimicrobial susceptibility test. In total, 60 A. viridans strains were cultured from dairy herds presenting with subclinical mastitis. The results of biochemical tests revealed that most of the isolates (75.0%) were accurately identified by API Rapid 20 Strep system and the majority of A. viridans strains (96.7%) were found to be catalase negative, while two (3.3%) isolates were weakly positive. All isolates were resistant to trimethoprim-sulfamethoxazole, followed by streptomycin (96.7%), tetracycline (65.0%) and clindamycin (56.7%) by minimum inhibition concentration-determining broth microdilution technique. As compared to the sequence of 16S rRNA gene, both PFGE and RAPD showed their capacities to discriminate the intra-species diversity of A. viridans. Furthermore, most of the isolates obtained from the same herd or region belonged to the same major RAPD group, which indicated that RAPD is an appropriate assay for tracking the origins of isolates and epidemiological studies of A. viridans. This is a novel approach to use three molecular techniques and to compare their efficiency regarding the genetic diversity of A. viridans. The data suggest that A. viridans associated with subclinical mastitis has a considerable phenotypic and genotypic diversity.
Highlights
Aerococcus viridans is a gram positive coccus, which belongs to the family of Streptococcaceae under the genus of Aerococcus [1]
A total of 1,008 milk samples were collected from cows with subclinical mastitis from 19 different dairy farms
A. viridans isolates were recovered from 60 cows on 10 farms located in Hebei province and two municipalities (Beijing and Tianjin)
Summary
Aerococcus viridans is a gram positive coccus, which belongs to the family of Streptococcaceae under the genus of Aerococcus [1]. A. viridans is wide spread organism in the environment [2], but it has been clinically associated with different human and animal infections [5,6]. A. viridans has been often associated with aquatic animal infections, like gaffkemia in lobster [7], septicemia in sea turtles [8] and mortality in tilapia [9]. A. viridans is associated with bovine severe respiratory syndrome [11], and has been isolated from the milk of cows with subclinical and clinical mastitis [12,13,14]
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