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The penicillin resistance of Enterococcus faecalis JH2-2r results from an overproduction of the low-affinity penicillin-binding protein PBP4 and does not involve a psr-like gene

Centre d’Ingénierie des Protéines, Institut de Chimie, B6, Université de Liège, (Sart Tilman), B-4000 Liège, Belgium¹

Author for correspondence: Jacques Coyette. Tel: +32 4 366 33 99. Fax: +32 4 366 33 64. e-mail: jcoyette{at}ulg.ac.be

A penicillin-resistant mutant, JH2-2r (MIC 75 µg ml^-1), was isolated from Enterococcus faecalis JH2-2 (MIC 5 µg ml^-1) by successive passages on plates containing increasing concentrations of benzylpenicillin. A comparison of the penicillin-binding protein (PBP) profiles in the two strains revealed a more intensely labelled PBP4 in JH2-2r. Because the sequences of the JH2-2 and JH2-2r pbp4 genes were strictly identical, even in their promoter regions, this intensive labelling could only be associated with an overproduction of the low-affinity PBP4. No psr gene analogous to that proposed to act as a regulator of PBP5 synthesis in Enterococcus hirae and Enterococcus faecium could be identified in the vicinity of pbp4 in E. faecalis JH2-2 and JH2-2r. However, a psr-like gene distant from pbp4 was identified. The cloning and sequencing of that psr-like gene from both E. faecalis strains indicated that they were identical. It is therefore postulated that the PBP4 overproduction in E. faecalis JH2-2r results from the modification of an as yet unidentified factor.

Keywords: ß-lactam resistance, low-affinity PBP, PBP-synthesis repressor (psr) gene

Abbreviations: HMM, high molecular mass; LMM, low molecular mass; PBP, penicillin-binding protein

The GenBank accession numbers for the sequences reported in this paper are Y17797 for the 8·4 kb segment of pDML521; AJ290435 for pbp4 of E. faecalis JH2-2; AJ276231 and AJ276232 for the psr-like gene of E. faecalis JH2-2 or JH2-2r, respectively.

^a Present address: Laboratory of Human Histology, Institut A. Swaen, L3, Université de Liège, rue des Pitteurs 20, B-4020 Liège, Belgium.

^b Present address: Departamento de Microbiologia y Immunologia, Facultad de Farmacia y Bioquimica, Universidad de Buenos Aires, Junin 956, 1113 Buenos Aires, Argentina.

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