Abstract
Bovine mastitis caused by Streptococcus agalactiae continues to be one of the major veterinary and economic issues in certain areas of the world. The more prevalent S. agalactiae strains that cause bovine mastitis in China dairy farms belong to a number of bovine-adapted sequence types (STs) ST67, ST103 and ST568. However, it is unknown why these STs can emerge as highly prevalent clones in bovine dairy farms. Here, to determine if a variety of virulence characteristics were associated with these highly prevalent STs, the molecular and virulence characterization of 116 strains isolated from bovine, human, fish and environment were analyzed. Our data showed that all bovine-adapted strains could be assigned to capsular genotype Ia or II, and carried pilus island 2b, and lactose operon. Importantly, we demonstrated that the growth ability in milk, biofilm formation ability and adhesion ability to bovine mammary epithelial cells (BMECs) were significantly higher for all bovine-adapted strains compared to strains from other origins. Additionally, ST103 and ST568 strains exhibited significantly higher hemolytic activity and cytotoxicity than ST67 strains. In conclusion, our study provides substantial evidence for the hypothesis that the virulence characteristics including efficient growth in milk, elevated biofilm formation ability, together with strong adhesion ability might have favored the high prevalence of the STs in the bovine environment, whereas the hemolytic activity and cytotoxicity were not the crucial characteristics.
Highlights
Streptococcus agalactiae is a gram-positive bacterium that has been considered as an important pathogen frequently associated with mastitis in bovine [1], neonatal meningitis in human [2] and meningoencephalitis in fish [3]
The bovine isolates were grouped in CC67 and CC103 (ST103 and its single-locus variant (SLV) ST568), and human isolates were grouped in CC17, CC19 (ST19 and its SLV ST110), CC23 and CC337
We investigated the molecular characterization of 116 S. agalactiae strains isolated from bovine, human, fish and environment
Summary
Streptococcus agalactiae is a gram-positive bacterium that has been considered as an important pathogen frequently associated with mastitis in bovine [1], neonatal meningitis in human [2] and meningoencephalitis in fish [3]. An eradication has been implemented since 1960s to reduce the incidence of S. agalactiae mastitis in several European countries [6, 7]. In last several years, S. agalactiae mastitis reemerged and the occurrence frequency has increased again in Denmark, Norway and other Scandinavian countries [6, 7]. Especially in China, S. agalactiae has become one of the most frequently detected pathogens in cows diagnosed with subclinical mastitis [8]. Bovine mastitis infected by S. agalactiae is still prevalent in many dairy farms worldwide [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
