First evidence of polar flagella in Klebsiella pneumoniae isolated from a patient with neonatal sepsis

The genus Klebsiella belongs to the family Enterobacteriaceae, and is currently considered to be non-motile and non-flagellated. In the present work, 25 Klebsiella strains isolated from nosocomial infections were assessed for motility under different growth conditions. One Klebsiella isolate, KpBUAP021, demonstrated a swim-like motility phenotype. The K. pneumoniae genotype was confirmed by 16S rRNA and rpoB gene sequence analysis. Multilocus sequence typing analysis also revealed that the KpBUAP021 strain places it in the ST345 sequence type, and belongs to the phylogenetic Kpl group. Transmission electron microscopy and the Ryu staining technique revealed that KpBUAP021 expresses polar flagella. Finally, the presence of fliC, fliA and flgH genes in this K. pneumoniae strain was confirmed. This report presents the first evidence for flagella-mediated motility in a K. pneumoniae clinical isolate, and represents an important finding related to its evolution and pathogenic potential.

Ler and H-NS, regulators controlling expression of the long polar fimbriae of Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 colonizes the human intestine and is responsible for diarrheal outbreaks worldwide. Previously we showed that EHEC produces long polar fimbriae (LPF) and that maximum expression is observed during the exponential phase of growth at 37 degrees C and pH 6.5. In this study, we analyzed the roles of several regulators in the expression of LPF using the beta-galactosidase reporter system, and we found that H-NS functions as a transcriptional silencer while Ler functions as an antisilencer of LPF expression. Interestingly, deletion of the hns and ler genes in EHEC caused constitutive expression of the fusion reporter protein. Semiquantitative reverse transcription (RT)-PCR was also used to analyze LPF expression in the EHEC ler or hns mutant strain. The hns mutant exhibited an increase in lpf mRNA expression, while expression in the ler mutant was decreased, compared to that in the wild-type strain. Using primer extension analysis, we identified two potential transcriptional start sites within the regulatory region of lpf and located consensus hexamers of -10 (CAAGAT) and -35 (TTCAAA), which are commonly found in sigma(70)-dependent promoters. Further, we determined whether H-NS and Ler interact directly with the lpf promoter region by using purified His-tagged proteins and electrophoretic mobility shift assays. Our data are the first to show direct binding interactions between the H-NS and Ler proteins within the regulatory sequence of the lpf operon. Based on the electrophoretic mobility shift assay, RT-PCR, primer extension, and beta-galactosidase assay results, we concluded that the E. coli O157:H7 lpf operon possesses a promoter dependent on sigma(70), that H-NS binds to the regulatory sequence of lpfA and "silences" the transcription of lpf, and that Ler binds to the regulatory sequence and inhibits the action of the H-NS protein.