The viability of four strains of two strains of and one strain of exposed to hyperimmune and pre-colostrum porcine serum was examined. Viable cell numbers (cfu/ml) of the strains and a rough strain of (CSU-P-1) decreased by 99% and 99.99%, respectively, after exposure for 1 h to porcine hyperimmune serum. In contrast, smooth strains and the strain showed no significant decrease in viable cell numbers after the same treatment. strain CSU-P-1 also showed a 99% decrease in viable cell numbers after exposure to pre-colostrum porcine serum for 1 h whereas the other strains tested showed no decrease in viable numbers under the same conditions. Heating the hyperimmune and pre-colostrum serum at 56° for 30 min resulted in the loss of bactericidal activity suggesting the involvement of complement in both systems. Analysis of silver-stained SDS-PAGE profiles of lipoplysaccharide (LPS) extracted from the bacterial cells indicated that the smooth strains of and the strain possessed high mol. wt O-side chain-like material, whereas the strains and strain CSU-P-1 did not. Gel filtration of acid-hydrolysed LPS samples indicated two distinct carbohydrate peaks for the strains with high mol. wt O-side chain-like material, whereas the other strains each yielded one distinct peak. Western-blot analysis indicated a positive reaction for anti- antibodies to the high mol. wt O-side chain-like material of all serum-resistant strains used in this study. The serum resistance of smooth strains may be an important factor in their association with wound infections.


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