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Infection and Immunity, December 2000, p. 7028-7038, Vol. 68, No. 12
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Molecular Variation among Type IV Pilin (bfpA) Genes from Diverse Enteropathogenic Escherichia coli Strains

T. Eric Blank,1 Hailang Zhong,1 Alison L. Bell,2 Thomas S. Whittam,2 and Michael S. Donnenberg1,*

Division of Infectious Diseases, Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland 21201,1 and Institute of Molecular Evolutionary Genetics and Department of Biology, Pennsylvania State University, University Park, Pennsylvania 168022

Received 12 June 2000/Returned for modification 7 September 2000/Accepted 13 September 2000

Typical enteropathogenic Escherichia coli (EPEC) strains produce bundle-forming pili (BFP), type IVB fimbriae that have been implicated in EPEC virulence, antigenicity, autoaggregation, and localized adherence to epithelial cells (LA). BFP are polymers of bundlin, a pilin protein that is encoded by the bfpA gene found on a large EPEC plasmid. Striking sequence variation has previously been observed among type IV pilin genes of other gram-negative bacterial pathogens (e.g., Pseudomonas and Neisseria spp.). In contrast, the established sequences of bfpA genes from two distantly related prototype EPEC strains vary by only a single base pair. To determine whether bundlin sequences vary more extensively, we used PCR to amplify the bfpA genes from 19 EPEC strains chosen for their various serotypes and sites and years of isolation. Eight different bfpA alleles were identified by sequencing of the PCR products. These alleles can be classified into two major groups. The alpha  group contains three alleles derived from strains carrying O55, O86, O111, O119, O127, or O128 somatic antigens. The beta  group contains five alleles derived from strains carrying O55, O110, O128ab, O142, or nontypeable antigens. Sequence comparisons show that bundlin has highly conserved and variable regions, with most of the variation occurring in the C-terminal two-thirds of the protein. The results of multilocus enzyme electrophoresis support the hypothesis that bfpA sequences have spread horizontally across distantly related clonal lineages. Strains with divergent bundlin sequences express bundlin protein, produce BFP, and carry out autoaggregation and LA. However, four strains lack most or all of these phenotypes despite having an intact bfpA gene. These results have important implications for our understanding of bundlin structure, transmission of the bfp gene cluster among EPEC strains, and the role of bundlin variation in the evasion of host immune system responses.

* Corresponding author. Mailing address: Division of Infectious Diseases, Department of Medicine, University of Maryland School of Medicine, 10 South Pine St., Medical School Teaching Facility 9-00, Baltimore, MD 21201. Phone: (410) 706-7560. Fax: (410) 706-8700. E-mail: mdonnenb{at}umaryland.edu.

Infection and Immunity, December 2000, p. 7028-7038, Vol. 68, No. 12
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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