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Infect. Immun. doi:10.1128/IAI.00356-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A tripartite efflux pump involved in gastrointestinal colonization by Klebsiella pneumoniae confers a tolerance response to inorganic acid

Univ Clermont 1, UFR Pharmacie, Laboratoire de Bactériologie, Clermont-Ferrand, France

^* To whom correspondence should be addressed. Email: Christiane.forestier{at}u-clermont1.fr.

	Abstract

Colonization of the gastrointestinal tract of patients by the opportunistic gram-negative bacilli Klebsiella pneumoniae generally occurs prior to the development of nosocomial infections. Mutant strain C-81 was isolated owing to its reduced capacity to colonize the digestive tract in a murine model following transposon mutagenesis (17). Nucleotide sequence analysis showed the transposon had inserted into the first open reading frame, eefA, of a three-gene locus (eefABC) whose homologue encodes a tripartite efflux pump in Enterobacter aerogenes (18), and this operon includes an additional short (183 bp) potential ORF, eefX, upstream of eefA. In vivo assays showed that a eefA isogenic mutant strain normally colonized the gastrointestinal tract in single-strain tests but was significantly impaired in competition against wild-type strain LM21. Although the cecum was the compartment with the highest number of CFU, the eefA mutant was also detected in the stomach in smaller numbers than the wild-type strain. Expression of this potential efflux pump could not be linked to any antimicrobial drug resistance phenotype, but conferred on the bacteria an acid tolerance response to inorganic acid. Expression of the eef promoter region, measured via a lacZ reporter construction, was slightly induced by an acidic environment and also by hyperosmolarity but not by the presence of bile salts. These results suggest that an efflux pump can confer measurable ecological benefits on K. pneumoniae in an environment with high competition potential.