title: The expression of a putative exotoxin and an ABC transporter during bovine intramammary infection contributes to the virulence of Staphylococcus aureus.
abstract: Staphylococcus aureus is a leading cause of intramammary infections (IMI) and bovine mastitis is an important disease for the dairy industry. As this bacterium probably expresses specific genes for establishment of IMI, we studied the transcriptional profile of four S. aureus strains recovered from experimentally infected cows. Microbial RNA was extracted from bacteria isolated from milk, reverse-transcribed and labeled for hybridization to sub-genomic microarrays to detect candidate genes for further investigations. Several S. aureus genes were expressed during IMI; some were detected in samples from more than one strain, more than one cow and at more than one time point during infection. A selection of four genes showing strong expression and with putative functions in pathogenesis was further studied by qPCR. By comparing the expression in different media in vitro, we found that gene SACOL2171 was induced by iron restriction whereas the expression of the transcriptional regulator SACOL2325 and the ABC transporter SACOL0718-720 (vraFG) were induced by milk. In addition, the putative exotoxin SACOL0442 seemed to require the intramammary environment for expression. Gene-disrupted mutants for SACOL0720 and SACOL0442 showed no growth defect in vitro but were attenuated during bovine IMI, causing infections with significant reductions in bacterial and somatic cell counts. The milk from the mammary quarters infected with these mutants also showed better appearance and composition than milk from quarters infected with the wild type. In conclusion, we have identified genes that are most likely important for S. aureus IMI. These represent novel candidates to include in a vaccine.
authors.affiliation: Centre d'Étude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
authors.forename: Marianne
authors.initials: M
authors.lastname: Allard
authors.affiliation: Centre d'Étude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
authors.forename: Céline
authors.initials: C
authors.lastname: Ster
authors.affiliation: Centre d'Étude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada.
authors.forename: Christian L
authors.initials: CL
authors.lastname: Jacob
authors.affiliation: Faculté de Médecine Vétérinaire, Université de Montréal, C.P. 5000, Saint-Hyacinthe, QC, J2S 7C6, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Scholl
authors.affiliation: Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, P.O. Box 1000, Agassiz, BC, V0M 1A0, Canada.
authors.forename: Moussa S
authors.initials: MS
authors.lastname: Diarra
authors.affiliation: Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, 2000 College, Sherbrooke, QC, J1M 0C8, Canada. Electronic address: Pierre.Lacasse@agr.gc.ca.
authors.forename: Pierre
authors.initials: P
authors.lastname: Lacasse
authors.affiliation: Centre d'Étude et de Valorisation de la Diversité Microbienne (CEVDM), Département de biologie, Faculté des sciences, Université de Sherbrooke, Sherbrooke, QC, J1K 2R1, Canada. Electronic address: Francois.Malouin@usherbrooke.ca.
authors.forename: François
authors.initials: F
authors.lastname: Malouin
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics; D000818:Animals; D002417:Cattle; D005098:Exotoxins / Q000096:biosynthesis* / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling / Q000662:veterinary; D008321:Mammary Glands, Animal / Q000382:microbiology; D008414:Mastitis, Bovine / Q000382:microbiology*; D008892:Milk / Q000382:microbiology; D016254:Mutagenesis, Insertional; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism / Q000472:pathogenicity*; D014774:Virulence
chemical_list: D018528:ATP-Binding Cassette Transporters; D005098:Exotoxins