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J. Dairy Sci. 86:2373-2381
© American Dairy Science Association, 2003.

Differential Expression of the Lactose Transporter Gene Affects Growth of Staphylococcus aureus in Milk

M. V. Sharer, C. Su, N. V. Hegde, B. M. Jayarao and L. M. Sordillo

Department of Veterinary Science, The Pennsylvania State University, University Park 16802

Corresponding author:
L. M. Sordillo; e-mail:
lms10{at}psu.edu.

In this study, differential display polymerase chain reaction (PCR) was used to search for unique or enhanced expression of genes in prevalent bovine mastitis-causing Staphylococcus aureus strains. Comparison of a pair of prevalent and rare strains revealed the differential expression of several genes. The lactose-specific permease, enzyme II (EII), was highly expressed in the prevalent strain. This gene was selected for further study due to its potential influence on bacterial growth, because lactose is the primary carbohydrate in milk. Growth analysis illustrated that prevalent strains reach significantly higher growth densities sooner than rare strains. Quantitative competitive reverse transcription PCR (QC RT-PCR) revealed increased EII mRNA expression in prevalent strains as compared to rare strains. Mutation of the EII gene resulted in abrogated growth and decreased EII mRNA expression in media containing lactose. These data suggest that increased EII expression may facilitate the pathogenesis of S. aureus mastitis by enhancing growth. This study is the first to implicate EII as a potential virulence factor in mastitis, and therefore may be useful in the development of novel therapeutic strategies against S. aureus mastitis.

Key Words: lactose transporter • Staphylococcus aureus • mastitis

Abbreviation key: agr = accessory gene regulator, BLAST = Basic Local Alignment Search Tool, CcpA = catabolite control protein, Cm = chloramphenicol, dNTP = deoxynucleotide triphosphate, EII = enzyme II, GAPDH = glyceraldehyde-3-phosphate dehydrogenase, lac = lactose operon, MMLV-RT = moloney murine leukemia virus reverse-transcriptase, ORF = open reading frame, PTS = phosphotransferase system, QC RT-PCR = quantitative-competitive reverse-transcriptase PCR, TSA = tryptic soy agar, TSB = tryptic soy broth, TSST-1 = toxic shock syndrome toxin-1






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