bfpAnegative

bfpAnegative is a designation used in microbiology to describe strains or samples that do not carry a functional bfpA gene, and therefore do not produce bundle-forming pili. In Enteropathogenic Escherichia coli (EPEC), bfpA encodes the major pilin subunit of the bundle-forming pilus (BFP); the BFP mediates the localized adherence pattern on epithelial cells and is located on the EPEC adherence factor (EAF) plasmid. The "negative" designation typically reflects loss of the EAF plasmid or disruption or mutation of the bfpA gene, resulting in no BFP expression.

Regarding phenotype and virulence, bfpAnegative strains generally fail to produce BFP and do not display the characteristic localized adherence on HEp-2 cells; they may rely on other virulence determinants, such as the LEE-encoded type III secretion system, for pathogenic interactions. The presence or absence of bfpA is used to distinguish typical EPEC (bfpA positive) from atypical EPEC (often bfpA negative). However, atypical EPEC can still cause disease, and virulence is multifactorial.

Detection and research: bfpA status can be determined by PCR for the bfpA gene, by plasmid profiling, or by phenotypic assays of pili formation. In laboratory studies, bfpAnegative strains serve as controls to investigate the contribution of BFP to adherence and pathogenesis.

The concept is primarily used in discussions of EPEC classification and virulence factor analysis, and reflects the broader distinction between BFP-producing and non-BFP-producing strains within the species.