The sialic acid-containing lipopolysaccharides of Salmonella djakarta and Salmonella isaszeg (serogroup O: 48): Chemical characterization and reactivity with a sialic acid-binding lectin from Cepaea hortensis

Abstract Lipopolysaccharides (LPS) of Salmonella djakarta and Salmonella isaszeg , as well as of a spontaneous R-mutant of S. djakarta were investigated as to their content in neuraminic acid (Neu) and its individual linkage. The two Salmonella serovars both belong to the O:48 serogroup of Salmonella , but to two different subgroups. LPS of both S-forms contained high amounts of Neu, although in different quantities, whereas the R-form was completely devoid of it. Methylation analysis indicated that Neu is exclusively terminally linked in S. djakarta whereas both terminal and 4-linked Neu were recognized in S. isaszeg . Although terminally linked, a sialidase from Arthrobacter ureafaciens was unable to split Neu even after prolonged incubation from both S-type LPSs. When LPS was first treated by mild alkali, however, the total amount of Neu from S. djakarta LPS and about 50% from that of LPS of S. isaszeg could be removed. In contrast, alkali-treated LPS, but also the non-treated one, proved to be effective inhibitors for a sialic acid-binding lectin from Cepaea hortensis . The resistance of terminal Neu towards sialidase may be due to the presence of an O-acetyl group which would be removed during the methylation analysis but would, especially when linked to C-4, not interfere with the reactivity of the lectin.