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An Early Response to Environmental Stress Involves Regulation of OmpX and OmpF, Two Enterobacterial Outer Membrane Pore-Forming Proteins

Myrielle Dupont, Chloë E. James, Jacqueline Chevalier, and Jean-Marie Pagès^*

UMR-MD1, IFR48, Facultés de Médecine et de Pharmacie, Université de la Méditerranée, Marseille, France

Received 24 November 2006/ Returned for modification 2 February 2007/ Accepted 20 June 2007

Bacterial adaptation to external stresses and toxic compounds is a key step in the emergence of multidrug-resistant strains that are a serious threat to human health. Although some of the proteins and regulators involved in antibiotic resistance mechanisms have been described, no information is available to date concerning the early bacterial response to external stresses. Here we report that the expression of ompX, encoding an outer membrane protein, is increased during early exposure to drugs or environmental stresses. At the same time, the level of ompF porin expression is noticeably affected. Because of the role of these proteins in membrane permeability, these data suggest that OmpF and OmpX are involved in the control of the penetration of antibiotics such as ß-lactams and fluoroquinolones through the enterobacterial outer membrane. Consequently, the early control of ompX and ompF induced by external stresses may represent a preliminary response to antibiotics, thus triggering the initial bacterial line of defense against antibiotherapy.

Published ahead of print on 2 July 2007.

M.D. and C.E.J. contributed equally to this study.