Streptococcus spp. and related bacteria: Their identification and their pathogenic potential for chronic mastitis – A molecular approach

• Published in: Research in veterinary science Vol. 91; no. 3; pp. 349 - 357
• Main Authors: Wyder, A.B., Boss, R., Naskova, J., Kaufmann, T., Steiner, A., Graber, H.U.
• Format: Journal Article
• Language: English
• Published: England Elsevier India Pvt Ltd 01-12-2011; Elsevier Limited
• Subjects: Aerococcus; Aerococcus viridans; Animal reproduction; Animals; Bacteria; Cattle; Chronic Disease; Enterococcus; Female; Identification systems; Lactation; Lactococcus; Lactococcus garvieae; Mastitis; Mastitis, Bovine - microbiology; Microbiology; Milk; Phylogeny; RNA, Bacterial - genetics; RNA, Ribosomal, 16S; Sequencing; Staphylococcus; Streptococcus - classification; Streptococcus - isolation & purification; Streptococcus agalactiae; Streptococcus dysgalactiae; Streptococcus spp; Streptococcus uberis; Veterinary medicine; Mastitis; Streptococcus spp; Cattle; Sequencing
• ISSN: 0034-5288; 1532-2661
• DOI: 10.1016/j.rvsc.2010.09.006

Streptococcus spp. and related bacteria form a large group of organisms which are associated with bovine intramammary Infections (IMI). Some of them are the well-known mastitis pathogens
Streptococcus uberis and
Streptococcus agalactiae. In addition, there are a considerable number of these gram-positive, catalase-negative cocci (PNC) with unclear mastitic pathogenicity such as
Aerococcus viridans which make the conventional diagnostics of PNC difficult. One diagnostic, API 20 Strep (API, Biomérieux) is recommended which, as a phenotypic assay, involves a series of miniaturized biochemical tests. Recently, preference is given to genotypic identification methods. In particular, sequencing of the 16S rRNA gene allows highly reproducible and accurate identification of bacteria and permits discovery of novel, clinically relevant bacteria. As a consequence, the aim of the present study was to compare identification of IMI-associated PNC by the API method as well as by sequencing of their 16S rRNA gene (16S). Furthermore, the correlation of these bacteria to bovine chronic mastitis and their phylogeny was investigated.
102 PNC isolated from single quarter milk samples were identified by API and 16S sequencing. Considering
Streptococcus uberis,
Streptococcus dysgalactiae subsp.
dysgalactiae and
Streptococcus agalactiae, both methods generated fully concordant results. In contrast, a very high disconcordance was observed for most of the other PNC, in particular
Enterococcus spp.,
Aerococcus viridans and the viridans streptococci were shown as apathogenic.
Lactococcus garvieae was found to be an opportunistic pathogen causing IMI during late lactation. In addition, PNC isolated from milk were frequently observed together with other bacteria, in particular with
Staphylococcus spp. In these cases, the levels of somatic cell counts (SCC) were determined by the specific PNC present in the sample. Considering PNC phylogeny based on 16S sequencing, 3 major clusters were observed. They included all the common mastitis pathogens (cluster I), the
Lactococcus spp.,
Enterococcus spp. and
Aerococcus spp. (cluster II) and all the viridans streptococci (cluster III).