Bactericidal activity of normal bovine serum (NBS) directed against some Enterobacteriaceae with sialic acid-containing lipopolysaccharides (LPS) as a component of cell wall

The sensitivity of bacteria to the bactericidal activity of serum depends on the structure and organization of the bacterial outer membrane. Sialic acid has been found in the O-specific region of bacterial lipopolysaccharide (LPS) and it plays an essential role in protecting Gram-negative bacteria against the bactericidal activity of human and animal serum. The susceptibility of Gram-negative bacilli with sialic acid-containing LPS to the bactericidal action of normal bovine serum (NBS) was determined. The examined strains (Escherichia coli O104 (PCM 270), E. coli O24 (PCM 195), E. coli O56 (PCM 2372), Citrobacter braakii O37 (PCM 2346) and Salmonella enterica ssp. enterica serovar Toucra O48 (PCM 2359) showed variable sensitivity to the bactericidal effect of the serum. The role of the mechanisms of complement activation in the killing process was also determined.