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Expression of two distinct types of pili by a hospital-acquired Enterococcus faecium isolate

¹ Department of Medical Microbiology, University Medical Center Utrecht, Heidelberglaan 100, Rm G04.614, 3584 CX, Utrecht, The Netherlands
² Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Heidelberglaan 100, Rm G04.614, 3584 CX, Utrecht, The Netherlands

Correspondence
Antoni P. A. Hendrickx
a.hendrickx{at}umcutrecht.nl

Surface filamentous structures designated pili, and implicated in virulence, have been found on the surfaces of several Gram-positive pathogens. This work describes the conditional expression of two phenotypically distinct pilus-like structures, designated PilA and PilB, on the surface of a hospital-adapted Enterococcus faecium bloodstream isolate. E. faecium is an emerging Gram-positive opportunistic pathogen that can cause severe disease, particularly in immunocompromised patients. Expression of PilA- and PilB-type pili was analysed during different phases of growth in broth culture. During growth, PilA and PilB pilin subunits were expressed around the cross-wall in early-exponential-phase cells. Polymerization and migration of short PilB-type pili towards the poles occurred in cells from the exponential phase and long polymerized pili were expressed at the poles of cells grown to stationary phase. In contrast, PilA-type pili were not expressed in broth culture, but only when cells were grown on solid media. Furthermore, surface expression of the PilA- and PilB-type pili was regulated in a temperature-dependent manner, as polymerization of two distinct types of pili at the surface only occurred when cells were grown at 37 °C; no pili were observed on cells grown at 21 °C. Hospital-aquired E. faecium isolates were specifically enriched in pilin gene clusters, suggesting that conditional expression of pili may contribute to E. faecium pathogenesis.

The GenBank/EMBL/DDBJ accession numbers for the DNA sequences of PGC-1 and PGC-3 of E. faecium strain E1165 reported in this article are EU909697 and EU909696.