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Authors’ contributions DM, FL and JPF carried out all PCR experiments. OF performed statistical studies. HS and VDG helped to draft the manuscript with the assistance of all authors. JD and GC conceived and coordinated the study. All authors read and approved the manuscript.”
“Background Streptococcus pneumoniae is one of the main aetiological agents of invasive infectious disease. Penicillin-resistant pneumococci were first observed in the 70s, and resistance to penicillin and multidrug-resistance have since then increased worldwide. Cell-wall biosynthetic enzymes named Penicillin Binding Proteins (PBP) are the targets for β-lactam antibiotics; mutations in these proteins constitute a major mechanism of resistance in clinical isolates. In laboratory strains, murMN, ciaRH and Cetuximab clinical trial cpoA genes are also involved in penicillin susceptibility
suggesting their involvement in cell wall metabolism [1–3]. One of the first steps of cell wall biosynthesis is catalysed by the
phosphoglucosamine mutase GlmM . In Escherichia coli, GlmM is activated by phosphorylation and it has been shown, in vitro, that GlmM of S. pneumoniae is a substrate for the serine/threonine kinase Stk, suggesting a role for StkP in cell wall metabolism [5, 6]. StkP protein from S. pneumoniae contains a eukaryotic kinase domain (Hanks kinase domain) and a PASTA (penicillin-binding protein and serine threonine kinase) domain signature only found in prokaryotes and putatively involved in cell wall sensing . In this study we evaluate the role of StkP in β-lactam susceptibility both in “”the model laboratory strain Cp1015″” and in natural clinical isolates carrying different PBP alleles. Methods Bacterial strains, ioxilan plasmids and growth conditions The plasmids and strains used in this study are described in Table 1. Escherichia coli was grown in LB (Difco, Sparks, Maryland) supplemented or not with ampicillin (100 μg ml-1) (Atral, Castanheira do Ribatejo, Portugal). S. pneumoniae clinical isolates were grown at 35°C on Columbia agar plates supplemented with 5% horse blood (Biomerieux, Carnaxide, Portugal), in an atmosphere enriched with 5% CO2. Serotyping was performed by the Quellung reaction with antisera produced by the Statens Seruminstitut, Copenhagen, Denmark .