Loss of resistance to ingestion and phagocytic killing by O(-) and K(-) mutants of a uropathogenic Escherichia coli O75:K5 strain.
To determine the importance of the O75 O antigen and the K5 capsular antigen in resistance to phagocytosis and phagocytic killing, we used previously described O75(-) and K5(-) mutants from an O75(+) K5(+) wild-type uropathogenic Escherichia coli strain in phagocytosis assays with polymorphonuclear leukocytes (PMNs) and monocytes. At a 10-to-1 ratio of bacteria to phagocytes and in the presence of 10% serum, the parental strain GR-12 was resistant to both PMNs and monocytes over a 2-h incubation period. The O75(-) and K5(-) mutants were similar in sensitivity to killing by both PMNs and monocytes, decreasing in viability by 80% in the first hour. Yet, a significant difference in killing between the O75(-) and K5(-) mutants was observed in the first 15 min of incubation. The K5(-) mutant decreased in numbers by almost 60%, while the O75(-) mutant increased in numbers similarly to GR-12 in the first 15 min. The difference in killing was found not to be due to the rate of opsonization. To further determine the mechanism of resistance, a fluorescence assay was used to differentiate attached and internalized bacteria. The K5 capsule hindered the association of both the wild-type strain and the O75(-) mutant in the initial incubation time with PMNs. In conclusion, both the K5 capsule and O75 O antigen play crucial roles in resistance to phagocytosis over time.
Burns
S M
SM
Department of Microbiology and Immunology, Baylor College of Medicine, Houston, Texas 77030, USA. sb691010@bcm.tmc.edu
Hull
S I
SI
D000942:Antigens, Bacterial; D000954:Antigens, Surface / Q000276:immunology*; D001422:Bacterial Adhesion; D004926:Escherichia coli / Q000276:immunology*; D006801:Humans; D009000:Monocytes / Q000276:immunology; D009154:Mutation; D009504:Neutrophils / Q000276:immunology; D019081:O Antigens / Q000276:immunology*; D010587:Phagocytosis
D000942:Antigens, Bacterial; D000954:Antigens, Surface; C030659:K antigens; D019081:O Antigens