Bovine mastitis is one of the most costly dairy-based diseases worldwide. Streptococcus uberis is a prevalent causative organism of mastitis and resides naturally in the environment of the dairy cow making prevention of the disease difficult. New strategies need to be developed to control this pathogen. However, a fundamental understanding of the complex relationships that exist between the cow, the pathogen and the environment are required in order to advance the development of prevention strategies. Microarray technology was used to evaluate the complex transcriptional changes which occur in the bovine mammary gland following the onset of clinical S. uberis mastitis. A 22,000 bovine cDNA microarray indicated that S. uberis mastitis led to the up-regulation of 1,283 genes and the down-regulation of 1,237 genes by greater than 1.5 fold. Gene ontology analysis demonstrated that S. uberis mastitis was typically associated with the up-regulation of genes that are involved in the immune response and homeostasis and a down-regulation of genes involved in lipid metabolism. Quantitative real-time analyses for a selection of genes associated with the immune response validated the microarray data. Mammary epithelial cell cultures did not show an increase in the expression of any of these immune factors in response to the same S. uberis strain used to induce clinical mastitis. This indicates that the expression of immune-related genes by mammary epithelial cells may be initiated by host factors and not S. uberis.
The application of bacteriocins, proteinaceous antimicrobials produced by bacteria which typically inhibit the same or closely-related species to that of the producer organism, has been suggested as one possible approach in the control of mastitis. S. uberis have been previously found to commonly produce bacteriocin-like inhibitory substances (BLIS). The BLIS activities of a set of fifteen S. uberis and S. bovis strains were assessed. The results confirmed the prolific and varied nature of BLIS production by S. uberis and S. bovis and also indicated that these strains may commonly produce more than one inhibitory agent. This survey of BLIS production led to the detection and characterisation of a novel circular bacteriocin, uberolysin, produced by S. uberis strains 233 and 42. The structural gene of uberolysin was subsequently identified in nine (64%) of the fifteen test strains.
Multiplex PCR analysis showed that 93% of 158 New Zealand S. uberis isolates contained the structural genes of at least one of the four known S. uberis bacteriocins (uberolysin, nisin U, ubericin A and ubericin 63). However, no apparent direct association was identified between any one of these bacteriocin-related loci and apparent ability to cause mastitis on New Zealand dairy farms. The uberolysin structural gene was detected in 91% of the isolates and this widespread distribution prompted the advancement and evaluation of a potential role for uberolysin in immunomodulation within the bovine mammary gland. Two different preparations of uberolysin were found to have different stimulatory effects on monocytes, neutrophils and epithelial cells. The less highly purified preparation appeared to diminish the production of TNF-α by monocytes in the presence of a bacterial stimulus and to decrease neutrophil phagocytosis. By contrast, the relatively more highly purified preparation of uberolysin itself induced a significant immune response by monocytes. Consistent with this, the purer preparation of uberolysin induced an increase in C3, IL-1β, IL-6, IL-8, the β-defensin LAP, the acute-phase protein MSAA, the calcium-binding protein S100A12 and TLR2 by quantitative real-time analysis.
Although currently only two S. uberis bacteriocins (uberolysin and nisin U) have been fully characterised, the present study has shown that this species may be an important source of novel antimicrobials. Furthermore, bacteriocin production by S. uberis may have an immunomodulation role within the mammary gland. A better understanding of the complex immune response initiated at the onset of clinical S. uberis mastitis and of the role that bacteriocins have in S. uberis pathogenesis may lead to development of improved strategies to combat this disease.
| Identifer | oai:union.ndltd.org:ADTP/217838 |
| Date | January 2008 |
| Creators | Swanson, Kara M, n/a |
| Publisher | University of Otago. Department of Microbiology & Immunology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Kara M Swanson |
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