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Infection and Immunity, August 1999, p. 3757-3762, Vol. 67, No. 8
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Loss of Resistance to Ingestion and Phagocytic Killing by Ominus and Kminus Mutants of a Uropathogenic Escherichia coli O75:K5 Strain

Stacy M. Burns,* and Sheila I. Hull

Department of Microbiology and Immunology, Baylor College of Medicine, Houston, Texas 77030

Received 25 January 1999/Returned for modification 22 March 1999/Accepted 6 May 1999

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.


* Corresponding author. Mailing address: Department of Microbiology and Immunology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: (713) 798-4021. Fax: (713) 798-7375. E-mail: sb691010{at}bcm.tmc.edu.


Infection and Immunity, August 1999, p. 3757-3762, Vol. 67, No. 8
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.



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