Growth Curve, Capsule Expression and Characterization of the Capsular Material of Selected Strains of Streptococcus uberis

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Abstract
The pattern of lectin agglutination, expression of capsule during the growth curve, and chemical composition of the capsule were examined in strains of Streptococcus uberis isolated from bovine mastitis. Lectin agglutination was conducted on 40 strains of S. uberis and 82.5% and 77.5% of the strains showed agglutination titers (> or = 1:128) with wheat germ agglutinin and concanavalin A, respectively. Capsule expression during the growth curve and its chemical composition was determined in one strain of S. uberis (UT 101), using a nonencapsulated strain of S. uberis (UT 102) as a negative control. Both strains were grown in Todd-Hewitt Broth (THB) with and without 20% milk whey. Strain UT 101 grown in THB or THB with 20% whey showed maximum numbers of colony forming units per ml (cfu/ml) at 12 hours, with a lag phase ending after 2 hours of growth. Maximum cfu/ml of UT 102 in THB was at 14 hours and 16 hours in THB 20% whey with a lag phase that ended at 2 hours of growth. Higher number of viable bacteria and increased capsule expression of UT 101 were detected in suspensions grown in THB 20% whey than in THB alone. Capsule expression of S. uberis UT 101 was maximal at 10 hours and decreased after 12 hours of growth. In contrast, S. uberis UT 102 showed negligible percentage (< 2%) of encapsulated bacteria during the entire growth curve. Chemical analysis of capsular material and the pattern of lectin agglutination suggest that hyaluronic acid is the major component. These results will be useful for understanding the pathogenesis of infections caused by S. uberis.

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