Physicochemical surface properties and phagocytosis by polymorphonuclear leucocytes of different serogroups of Salmonella.

Salmonella isolates belonging to different serogroups have been analysed with respect to physicochemical surface properties and interaction with human polymorphonuclear granulocytes (PMNs). Most (22/34) recent isolates of the different serotypes showed hydrophilic surface properties and little if any negative charge accompanied by resistance to phagocytosis by PMN similar to the old laboratory S strains Salmonella typhimurium 395MS and Salmonella minnesota S99 (main group). However, all isolates belonging to the serogroups C1 (5 isolates), E4 (2), O43 (1), and one out of three E1 isolates (C1/E4 group) differed from the main group. In aqueous biphasic partition in dextran-polyethyleneglycol (PEG) systems the bacteria in the main group accumulated in the PEG-rich phase to 55-97%, those in the C1/E4 group to less than 10%, and R-mutants only to 1-2%. The bacteria in the C1/E4 group displayed a negative surface charge and a susceptibility to phagocytosis by PMNs that were greater than those for strains in the main group but much lower than those shown by the R-mutants. Bacteria belonging to serogroup C1 also displayed a significant susceptibility to hydrophobic interaction. The results are discussed in relation to the pathogenicity of salmonella.