Panton-Valentine leukocidin in pediatric community-acquired Staphylococcus aureus infections.

PURPOSE: Panton-Valentine Leukocidin (PVL) is an exotoxin produced by strains of Staphylococcus aureus (SA). Its importance as a virulence factor is controversial. We aim to further characterize the role of PVL in pediatric community-acquired SA infections. METHODS: In a cohort study conducted from July to November 2006, we prospectively collected all strains of SA isolated at the Montreal Children's Hospital causing community-acquired infections in children aged 18 years or younger. The strains were analyzed for the presence of the PVL encoding genes by PCR and were phage typed. Strains resistant to methicillin or pvl+ were analyzed by pulsed-field gel electrophoresis. A medical chart review blinded to patient pvl status was performed to retrieve demographic and clinical data. Data were analyzed by logistic regression. RESULTS: We identified 74 pediatric community-acquired SA infections. Nineteen strains (25.7%) were positive for the pvl genes. Four isolates (5.4%) were resistant to methicillin and three of these were pvl+. No predominant clone was identified by phage typing or pulsed field gel electrophoresis. Pvl+ and pvl- infections were statistically similar for patient age, hospital admission, length of hospital stay, invasive disease, intravenous antibiotics and outcomes. Pvl+ strains were more likely to cause abscesses (OR 20.79; 95% CI 4.93 - 87.58), less likely to cause superficial skin infections (OR 0.18; 95% CI 0.05 - 0.64) and less likely to be resistant to erythromycin (OR 0.048; 95% CI 0.004 - 0.52). CONCLUSIONS: In a clonally heterogeneous population of pediatric community-acquired SA infections, pvl+ strains were associated with abscess formation and erythromycin susceptibility, but not invasive disease.

Epidemiological, biochemical and antimicrobial susceptibility characteristics of Streptococcus pseudoporcinus isolated in Quebec, Canada, from 1997 to 2006.

From 1997 to 2006, in the province of Quebec, Canada, 15 isolates of Streptococcus pseudoporcinus from 1 urine and 14 vaginorectal cultures were recovered from the genitourinary tract of pregnant women. All these women originated from the Caribbean or sub-Saharan Africa (P=0.00045 compared with a suitable control group). The S. pseudoporcinus isolates were compared to eight isolates of Streptococcus porcinus identified in Quebec from 1995 to 2006, all from animals, of which five were swine. 16S rRNA gene sequencing was required to differentiate between S. pseudoporcinus and S. porcinus animal isolates.

Streptococcus pseudoporcinus sp. nov., a novel species isolated from the genitourinary tract of women.

Streptococcus strains from animal and human sources identified biochemically as Streptococcus porcinus were investigated by 16S rRNA gene sequencing. The nine human strains isolated between 1997 and 2005 formed a single cluster with more than 2.1% dissimilarity with S. porcinus strains from animal sources. A novel species, Streptococcus pseudoporcinus sp. nov., is proposed.

The N-terminal region of the CCAAT displacement protein (CDP)/Cux transcription factor functions as an autoinhibitory domain that modulates DNA binding.

The CCAAT displacement protein/Cut homeobox (CDP/Cux) transcription factor is expressed as multiple isoforms that may contain up to four DNA-binding domains: Cut repeats 1, 2, and 3 (CR1, CR2, CR3) and the Cut homeodomain (HD). The full-length protein, which contains all four DNA-binding domains, is surprisingly less efficient than the shorter isoforms in DNA binding. Using a panel of recombinant proteins expressed in mammalian or bacterial cells, we have identified a domain at the extreme N terminus of the protein that can inhibit DNA binding. This domain was able to inhibit the activity of full-length CDP/Cux and of proteins containing various combinations of DNA-binding domains: CR1CR2, CR3HD, or CR2CR3HD. Since inhibition of DNA binding was also observed with purified proteins obtained from bacteria, we conclude that autoinhibition does not require post-translational modification or interaction with an interacting protein but instead functions through an intramolecular mechanism. Antibodies directed against the N-terminal region were able to partially relieve inhibition. In vivo, the transition between the inactive and active states for DNA binding is likely to be governed by posttranslational modifications and/or interaction with one or more protein partners. In addition, we show that the relief of autoinhibition can be accomplished via the proteolytic processing of CDP/Cux. Altogether, these results reveal a novel mode of regulation that serves to modulate the DNA binding activity of CDP/Cux.

CDP/Cux stimulates transcription from the DNA polymerase alpha gene promoter.

CDP/Cux (CCAAT-displacement protein/cut homeobox) contains four DNA binding domains, namely, three Cut repeats (CR1, CR2, and CR3) and a Cut homeodomain. CCAAT-displacement activity involves rapid but transient interaction with DNA. More stable DNA binding activity is up-regulated at the G(1)/S transition and was previously shown to involve an N-terminally truncated isoform, CDP/Cux p110, that is generated by proteolytic processing. CDP/Cux has been previously characterized as a transcriptional repressor. However, here we show that expression of reporter plasmids containing promoter sequences from the human DNA polymerase alpha (pol alpha), CAD, and cyclin A genes is stimulated in cotransfections with N-terminally truncated CDP/Cux proteins but not with full-length CDP/Cux. Moreover, expression of the endogenous DNA pol alpha gene was stimulated following the infection of cells with a retrovirus expressing a truncated CDP/Cux protein. Chromatin immunoprecipitation (ChIP) assays revealed that CDP/Cux was associated with the DNA pol alpha gene promoter specifically in the S phase. Using linker scanning analyses, in vitro DNA binding, and ChIP assays, we established a correlation between binding of CDP/Cux to the DNA pol alpha promoter and the stimulation of gene expression. Although we cannot exclude the possibility that stimulation of gene expression by CDP/Cux involved the repression of a repressor, our data support the notion that CDP/Cux participates in transcriptional activation. Notwithstanding its mechanism of action, these results establish CDP/Cux as an important transcriptional regulator in the S phase.