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Infection and Immunity, November 1999, p. 6067-6075, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Enterococcus faecalis Bearing Aggregation Substance Is Resistant to Killing by Human Neutrophils despite Phagocytosis and Neutrophil Activation

Robert M. Rakita,1,2,* Natalie N. Vanek,1 Karen Jacques-Palaz,1 Mee Mee,1 M. Michele Mariscalco,3 Gary M. Dunny,4 Mark Snuggs,5 W. Barry Van Winkle,5 and Scott I. Simon3

Division of Infectious Diseases, Department of Internal Medicine,1 and Department of Pathology and Laboratory Medicine,5 University of Texas Medical School at Houston, and Speros P. Martel Section of Leukocyte Biology, Department of Pediatrics, Baylor College of Medicine,3 Houston, Texas 77030; Virginia Mason Medical Center, Seattle, Washington 981112; and Department of Microbiology, University of Minnesota Medical School, Minneapolis, Minnesota 554554

Received 1 April 1999/Returned for modification 24 May 1999/Accepted 26 August 1999

Enterococcus faecalis aggregation substance (AS) mediates efficient bacterium-bacterium contact to facilitate plasmid exchange as part of a bacterial sex pheromone system. We have previously determined that AS promotes direct, opsonin-independent binding of E. faecalis to human neutrophils (PMNs) via complement receptor type 3 and other receptors on the PMN surface. We have now examined the functional consequences of this bacterium-host cell interaction. AS-bearing E. faecalis was phagocytosed and internalized by PMNs, as determined by deconvolution fluorescence microscopy. However, these bacteria were not killed by PMNs, and internalized bacteria excluded propidium iodide, indicating intact bacterial membranes. Resistance to killing occurred despite activation of PMNs, as indicated by an increase in both functional and total surface Mac-1 expression, shedding of L-selectin, and an increase in PMN extracellular superoxide and phagosomal oxidant production. Deconvolution fluorescence microscopy also revealed that phagosomes containing AS-bearing bacteria were markedly larger than phagosomes containing opsonized E. faecalis, suggesting that some modification of phagosomal maturation may be involved in AS-induced resistance to killing. PMN phagosomal pH was significantly higher after ingestion of nonopsonized AS-bearing E. faecalis than after that of opsonized bacteria. The novel ability of AS to promote intracellular survival of E. faecalis inside PMNs suggests that AS may be a virulence factor used by strains of E. faecalis.

* Corresponding author. Mailing address: Virginia Mason Medical Center, 1100 Ninth Ave., P.O. Box 900 (Mail Stop: C7-PUL), Seattle, WA 98111. Phone: (206) 341-0846. Fax: (206) 223-6814. E-mail: cidrmr{at}vmmc.org.

Infection and Immunity, November 1999, p. 6067-6075, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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