Biological Characteristics and Pathogenicity of Helcococcus ovis Isolated From Clinical Bovine Mastitis in a Chinese Dairy Herd.

Helcococcus ovis (H. ovis) was first reported in ovine subclinical mastitis milk and post-mortem examination organs in Spain and the United Kingdom in 1999; subsequently, it appeared in cattle, horse, goat, and human. However, isolation and characterization of the pathogen from clinical bovine mastitis is unknown. The objective of this study was to identify the pathogen in clinical bovine mastitis. A total of four strains were isolated from bovine mastitis milk samples from a Chinese dairy farm, and they were identified as H. ovis by microscopic examination and 16S rRNA gene sequencing. Phylogenetic tree was constructed using 16S rRNA gene, and the isolates were closely related to other China strains and strains from Japan. The growth speed of the H. ovis isolated was relatively slower than Streptococcus agalactiae, and the phenotypic characteristics were similar to H. ovis CCUG37441 and CCUG39041 except to lactose. The isolates were sensitive to most of the common used antimicrobials. The H. ovis isolates could lead to mild murine mastitis alone and induce severe mastitis when co-infected with Trueperella pyogenes in the murine mammary infection model constructed.

Liu K ，Deng Z ，Zhang L ，Gu X ，Liu G ，Liu Y ，Chen P ，Gao J ，Han B ，Qu W ... -  《Frontiers in Veterinary Science》

Characterization of Streptococcus lutetiensis isolated from clinical mastitis of dairy cows.

Streptococcus lutetiensis, previously termed Streptococcus bovis type II/1, has rarely been associated with bovine mastitis. The objectives of this work were to characterize the molecular diversity, antimicrobial resistance profiles, virulence genes of Strep. lutetiensis (n = 37) isolated from bovine clinical mastitis, as well as its pathogenic effects in a murine mastitis model. Genetic relationships of isolates were determined by random amplified polymorphic DNA (RAPD)-PCR, virulence genes were detected by PCR. Antimicrobial susceptibility testing was carried out by broth microdilution technique. The pathogenic effects of Strep. lutetiensis were studied with 2 infection models: bovine mammary epithelial cells cultured in vitro and murine mammary infection in vivo. Streptococcus lutetiensis isolates were clustered into 5 RAPD-types (A-E), with a dominant type A representing 84% of isolates. Eighteen (49%), 16 (43%), and 9 (24%) isolates were resistant to ceftiofur, tetracycline, and erythromycin, respectively. Prevalence of multidrug resistance (resistant to ≥3 classes of antimicrobials) was 24% (9/37). The most prevalent virulence genes were bca (100%), speG (100%), hly (97%), scpB (95%), and ssa (95%). There was no difference between isolates from mild and moderate cases of bovine mastitis in prevalence of virulence genes. Streptococcus lutetiensis rapidly adhered to and subsequently invaded (1 and 3 h after infection, respectively) bovine mammary epithelial cells, resulting in elevated lactate dehydrogenase release (4 h after infection). Edema and hyperemia were observed in challenged mammary glands and bacteria were consistently isolated at 12, 24, and 48 h after infection. In addition, numerous neutrophils migrated into gland alveoli and interstitium of infected mammary tissue. We concluded that Strep. lutetiensis had potential to spread within a dairy herd and good adaptive ability in bovine mammary cells or tissue, which are generally characteristics of a contagious mastitis pathogen.

Chen P ，Qiu Y ，Liu G ，Li X ，Cheng J ，Liu K ，Qu W ，Zhu C ，Kastelic JP ，Han B ，Gao J ... -  《-》

Pangenomic and biochemical analyses of Helcococcus ovis reveal widespread tetracycline resistance and a novel bacterial species, Helcococcus bovis.

Cunha F ，Zhai Y ，Casaro S ，Jones KL ，Hernandez M ，Bisinotto RS ，Kariyawasam S ，Brown MB ，Phillips A ，Jeong KC ，Galvão KN ... -  《Frontiers in Microbiology》

Phenotypic and genotypic characterization of antimicrobial resistance profiles in Streptococcus dysgalactiae isolated from bovine clinical mastitis in 5 provinces of China.

Bovine mastitis is among the most prevalent and costly diseases of dairy animals and is caused by a variety of bacterial pathogens including Streptococcus dysgalactiae. However, comprehensive studies reporting the prevalence and antimicrobial resistance profiles of S. dysgalactiae isolated from bovine mastitis are scarce. Therefore, this study was to investigate the occurrence of S. dysgalactiae associated with bovine clinical mastitis, to assess their antimicrobial resistance profiles, and to analyze the phenotypic and genotypic profiling of resistant isolates. In total, 1,180 milk samples were collected from dairy cows with clinical mastitis belonging to 74 commercial dairy herds located in 14 provinces of China from January 2014 to May 2016. Overall S. dysgalactiae isolates were recovered from 88 (7.5%) of the mastitic milk samples. The antimicrobial susceptibility of these isolates was tested against 8 antimicrobial agents by using minimum inhibitory concentrations. Results showed that 82 (93.2%) isolates expressed resistance to more than one antimicrobial agent. Antimicrobial resistance was highest against kanamycin (89.8%), sulfonamide (83.0%), and streptomycin (58.0%), which can be attributed to the intrinsic resistance for most of Streptococcus spp. against those antimicrobial substances. Strikingly, 30 (34.1%) and 12 (13.6%) isolates were found resistant to cephalexin and ceftriaxone, respectively. BlaTEM, ermB, and tetM were the most prevalent resistance genes. All isolates carried at least one of all tested resistance genes. Also, 1.1, 12.5, 18.2, 36.4, and 31.8% of isolates were positive for at least one tested resistance gene in 1, 2, 3, 4, or 5 classes of antimicrobials. Survival analysis showed a significant association between ermB and survival of the S. dysgalactiae isolates at increasing erythromycin concentrations. No other statistically significant associations were observed between the phenotypic and genotypic resistance profiles. This study concludes a considerable prevalence of S. dysgalactiae associated with bovine mastitis in dairy herds of China and these isolates exhibited high resistance rates to tested antimicrobials, coupled with high occurrence of resistance genes. Both the prevalence of S. dysgalactiae and their antimicrobial resistance profiles strongly varied among dairy herds, demonstrating the need for antimicrobial susceptibility surveillance at the herd level to ensure optimal therapeutic results.

Zhang S ，Piepers S ，Shan R ，Cai L ，Mao S ，Zou J ，Ali T ，De Vliegher S ，Han B ... -  《-》

Characteristics of Aerococcus viridans isolated from bovine subclinical mastitis and its effect on milk SCC, yield, and composition.

Sun M ，Gao J ，Ali T ，Yu D ，Zhang S ，Khan SU ，Fanning S ，Han B ... -  《-》