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Effect of hydrolysable and condensed tannins on growth, morphology and metabolism of Streptococcus gallolyticus (S. caprinus) and Streptococcus bovis

Animal Science Department, University of Adelaide, Roseworthy Campus, Roseworthy, SA 5371, Australia¹

Author for correspondence: J. D. Brooker. Tel: +61 8 8303 7357. Fax: +61 8 8303 7114. e-mail: john.brooker{at}adelaide.edu.au

Streptococcus gallolyticus (S. caprinus) was resistant in vitro to at least 7% (w/v) tannic acid and 4% (w/v) acacia condensed tannin, levels 10-fold greater than those tolerated by S. bovis. Growth of S. gallolyticus in liquid medium was characterized by a lag period which increased, and a growth rate which decreased, with increasing tannin concentration. S. gallolyticus was also more tolerant to the presence of simple phenolic acid monomers than was S. bovis, but the lag period was still concentration dependent. Gallate decarboxylase activity in S. gallolyticus was elevated in the presence of tannic acid or gallic acid but not with other phenolic acids. Scanning electron microscopic analysis showed that both the size and shape of S. gallolyticus and S. bovis changed in response to tannin but only S. gallolyticus was surrounded by an extracellular polysaccharide matrix which accumulated in a tannin-concentration-dependent fashion. Washing of the cells to remove extracellular polysaccharide increased the lag period of S. gallolyticus in the presence of 1% (w/v) tannic acid from 4 h to 6 h. In contrast, increasing extracellular polysaccharide synthesis in S. bovis did not increase its tolerance to tannic acid. These data demonstrate that S. gallolyticus has developed a number of mechanisms to reduce the potential effect of tannins on cell growth, and that these mechanisms provide the organism with a selective advantage over S. bovis when grown in the presence of tannins.

Keywords: Streptococcus caprinus, hydrolysable tannins, extracellular polysaccharide matrix, tannin resistance, livestock

Abbreviations: CT, condensed tannin; ACT, acacia condensed tannin; EM, extracellular matrix; EPS, extracellular polysaccharide; mBHI, modified brain heart infusion; TA, tannic acid

^a Present address: Department of Pathology, University of Tasmania, Hobart, Tas 7000, Australia.

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