Comparative virulence of intra- and interstrain lipopolysaccharide variants of XXXX in the guinea pig model.

@entity6475 @entity4003 @entity221
We compared the relative infectivity and virulence of lipopolysaccharide (LPS) variants of the Nine Mile strain of @entity4003 with those of the Priscilla strain, a representative of @entity6475 . In agreement with results of previous studies, Nine Mile phase I (9mi/I) organisms were highly infectious, eliciting seroconversion and @entity221 with inocula containing as few as four organisms. Viable 9mi/I was recovered from the spleens of infected animals 30 days postinfection. Nine Mile phase II (9mi/II) organisms did not elicit @entity221 or seroconversion except with very large inocula, and viable organisms could not be recovered at 30 days postinfection. The Nine Mile/Crazy variant, bearing the intermediate-type LPS, was also highly infectious, as determined by @entity221 response and seroconversion, although, as with 9mi/II, viable organisms could not be recovered 30 days postinfection. The Priscilla strain in phase I (Pris/I) was as infectious as 9mi/I, as determined by seroconversion and its presence in the spleen 30 days postinfection; but in contrast to 9mi/I, more than 10(5) Pris/I isolates were required to induce @entity221 . The temporal appearances of anti-phase I and II antibodies were similar for the two strains. A variety of serological techniques measuring antibody response against whole-cell and purified LPS antigens in agglutination, immunofluorescence, enzyme-linked immunosorbent, and immunoblot assays did not demonstrate sufficient specificity to distinguish between 9mi/I and Pris/I infections. Results of vaccine cross-challenge experiments showed a significant degree of protection between homologous and heterologous challenge strains. protection between homologous
