COMPLEMENT MEDIATED LYSIS, ADHESION, INVASION, AND MULTIPLICATION WITHIN HeLa CELLS AND HUMAN MONOCYTE MACROPHAGES OF SUSCEPTIBLE AND MULTIPLE DRUG-RESISTANT S. typhi.

Twenty strains each of susceptible and multiple drug resistant strains of S. typhi were compared for susceptibility to complement lysis and cellular invasion. Drug resistant strains showed increased resistance to complement killing. Antibody increased the efficiency of complement killing of S. typhi. Susceptible and drug resistant strains showed almost the same rates of adherence and invasion of HeLa cells and human monocyte cell lines. However, the resistant strains showed a relatively higher rate of intracellular multiplication after 6 hours within human mononuclear macrophages. Decreased killing by complement and the relatively higher multiplication within mononuclear macrophages of the drug resistant strains may be the reason for their increased virulence.