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Microbiology. 1999 Mar;145 ( Pt 3):673-679. doi: 10.1099/13500872-145-3-673.

Porin expression in clinical isolates of Klebsiella pneumoniae.

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Área de Microbiología, Departamento de Biología, Universidad de las Islas Baleares, Palma de Mallorca, and Unidad de Recursos Naturales, Instituto Mediterráneo de Estudios Avanzados, IMEDEA (CSIC-UIB), Carretera de Valldemosa Km 7·5, E-07071 Palma de Mallorca, Spain.
Departamento de Microbiología, Universidad de Sevilla, Avenida Sánchez Pizjuan s/n, E-41080 Sevilla, Spain.
Servicio de Microbiología, Hospital Son Dureta, Andrea Doria 55, E-07014 Palma de Mallorca, Spain.
Departamento de Microbiología, Universidad de Barcelona, Avenida Diagonal 645, E-08071 Barcelona, Spain.


Two porins, OmpK36 and OmpK35, have been described previously in Klebsiella pneumoniae, and they are homologous to the Escherichia coli porins OmpC and OmpF, respectively, at both the DNA and amino acid levels. Optimal resolution of the two K. pneumoniae porins by electrophoresis on polyacrylamide gels is not achieved using gel systems already described for E. coli and requires modifications of the bisacrylamide content of the resolving gels. Once resolved, identification of porins OmpK36 and OmpK35 cannot be based solely on their apparent molecular masses since in some strains the OmpK36 porin migrates faster than the OmpK35 porin, whilst in other strains OmpK35 is the faster-migrating porin. Expression of OmpK35 porin is increased in low-osmolarity medium and, combined with Western blot analysis, this allows for the identification of both porins. Application of this identification system showed that most isolates lacking expression of extended-spectrum beta-lactamases express the two porins, whereas most isolates producing these beta-lactamases express only porin OmpK36, and the OmpK35 porin is either very low or not expressed.

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