Alpha- and β-casein components of host milk induce biofilm formation in the mastitis bacterium Streptococcus uberis.
Streptococcus uberis is an environmental udder pathogen that infects cattle and can cause persistent intramammary infection (IMI), despite the fact that isolates are mainly susceptible to antibiotics. As biofilm growth can cause persistent infection, the ability of ten S. uberis isolates from clinical and subclinical IMIs to form biofilms on the polystyrene surface of a conventional 96-microplates model was examined. Biofilm formation was judged by different staining methods (crystal violet and resazurin) and by atomic force and fluorescence microscopy. These analyses revealed that two out of ten S. uberis strains tested were able to form biofilms. Upon treatment with Proteinase K, biofilms of S. uberis were completely disintegrated, which indicates that biofilm formation is protein-mediated in these strains. Addition of trace amounts of milk, the natural growth medium of S. uberis, significantly increased biofilm formation by most of the strains initially classified as non-biofilm producers. Alpha-casein and β-casein were the primary inducers of biofilm growth, and casein degradation by serine protease activity was required to achieve maximal biofilm production. These results suggest that the extracellular proteolytic activity of S. uberis contributes to an increased biofilm formation. Such a mode of growth induced by host proteins might help to explain the persistence of IMIs caused by this pathogen.
Department of Veterinary Biosciences, P.O. Box 66, University of Helsinki, FI-00014, Helsinki, Finland.
Emilia
E
Varhimo
Pekka
P
Varmanen
Adyary
A
Fallarero
Malena
M
Skogman
Satu
S
Pyörälä
Antti
A
Iivanainen
Antti
A
Sukura
Pia
P
Vuorela
Kirsi
K
Savijoki
D000818:Animals; D018441:Biofilms / Q000187:drug effects; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D005260:Female; D008414:Mastitis, Bovine / Q000382:microbiology; D018625:Microscopy, Atomic Force; D008892:Milk / Q000382:microbiology*; D011480:Protease Inhibitors / Q000494:pharmacology; D013291:Streptococcus / Q000187:drug effects / Q000254:growth & development* / Q000302:isolation & purification
D002364:Caseins; D011480:Protease Inhibitors