16 research outputs found
Rapid evolution of virulence and drug resistance in the emerging zoonotic pathogen Streptococcus suis
Background: Streptococcus suis is a zoonotic pathogen that infects pigs and can occasionally cause serious infections in
humans. S. suis infections occur sporadically in human Europe and North America, but a recent major outbreak has been
described in China with high levels of mortality. The mechanisms of S. suis pathogenesis in humans and pigs are poorly
understood.
Methodology/Principal Findings: The sequencing of whole genomes of S. suis isolates provides opportunities to
investigate the genetic basis of infection. Here we describe whole genome sequences of three S. suis strains from the same
lineage: one from European pigs, and two from human cases from China and Vietnam. Comparative genomic analysis was
used to investigate the variability of these strains. S. suis is phylogenetically distinct from other Streptococcus species for
which genome sequences are currently available. Accordingly, ,40% of the ,2 Mb genome is unique in comparison to
other Streptococcus species. Finer genomic comparisons within the species showed a high level of sequence conservation;
virtually all of the genome is common to the S. suis strains. The only exceptions are three ,90 kb regions, present in the two
isolates from humans, composed of integrative conjugative elements and transposons. Carried in these regions are coding
sequences associated with drug resistance. In addition, small-scale sequence variation has generated pseudogenes in
putative virulence and colonization factors.
Conclusions/Significance: The genomic inventories of genetically related S. suis strains, isolated from distinct hosts and
diseases, exhibit high levels of conservation. However, the genomes provide evidence that horizontal gene transfer has
contributed to the evolution of drug resistance
An Outbreak of Severe Infections with Community-Acquired MRSA Carrying the Panton-Valentine Leukocidin Following Vaccination
Background: Infections with community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are emerging
worldwide. We investigated an outbreak of severe CA-MRSA infections in children following out-patient vaccination.
Methods and Findings: We carried out a field investigation after adverse events following immunization (AEFI) were reported. We reviewed the clinical data from all cases. S. aureus recovered from skin infections and from nasal and throat swabs were analyzed by pulse-field gel electrophoresis, multi locus sequence typing, PCR and microarray. In May 2006, nine children presented with AEFI, ranging from fatal toxic shock syndrome, necrotizing soft tissue infection, purulent abscesses, to fever
with rash. All had received a vaccination injection in different health centres in one District of Ho Chi Minh City. Eight children had been vaccinated by the same health care worker (HCW). Deficiencies in vaccine quality, storage practices, or preparation and delivery were not found. Infection control practices were insufficient. CA-MRSA was cultured in four children and from nasal and throat swabs from the HCW. Strains from children and HCW were indistinguishable. All carried the Panton-Valentine leukocidine (PVL), the staphylococcal enterotoxin B gene, the gene complex for staphylococcal-cassette-chromosome mec type V, and were sequence type 59. Strain HCM3A is epidemiologically unrelated to a strain of ST59 prevalent in the USA, althoughthey belong to the same lineage.
Conclusions. We describe an outbreak of infections with CA-MRSA in children, transmitted by an asymptomatic colonized HCW during immunization injection. Consistent adherence to injection practice guidelines is needed to prevent CA-MRSA transmission in both in- and outpatient settings
Chemical force microscopy of stimuli-responsive adhesive copolymers
Atomic force microscopy with chemically sensitive tips was used to investigate the hydrophobic and electrostatic interaction forces of a stimuli-responsive adhesive polymer, and their dynamic changes in response to water immersion and salt concentration. Block copolymer-filled coatings were obtained by incorporating an amphiphilic block copolymer containing a polydimethylsiloxane (PDMS) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix. Topographic images of fresh samples revealed the presence of nanoscale domains associated with the presence of copolymers,covered by a thin layer of PDMS. Prolonged (30 days) immersion in aqueous solution led to the exposure of the hydrophilic PDMAEMA chains on the surface. Using adhesion force mapping with hydrophobic tips, we showed that fresh samples were uniformly hydrophobic, while aged samples exhibited lower surface hydrophobicity and featured nanoscale hydrophilic copolymer domains. Force mapping with negatively charged tips revealed remarkable salt-dependent force plateau signatures reflecting desorption of polyelectrolyte copolymer chains. These nanoscale experiments show how solventinduced conformational changes of stimuli-responsive copolymers can be used to modulate surface adhesion
Distal Hydrophobic Loop Modulates the Copper Active Site and Reaction of AA13 Polysaccharide Monooxygenases
Polysaccharide
monooxygenases (PMOs) use a type-2 copper
center
to activate O2 for the selective hydroxylation of one of
the two C–H bonds of glycosidic linkages. Our electron paramagnetic
resonance (EPR) analysis and molecular dynamics (MD) simulations suggest
the unprecedented dynamic roles of the loop containing the residue
G89 (G89 loop) on the active site structure and reaction cycle of
starch-active PMOs (AA13 PMOs). In the Cu(II) state, the G89 loop
could switch between an “open” and “closed”
conformation, which is associated with the binding and dissociation
of an aqueous ligand in the distal site, respectively. The conformation
of the G89 loop influences the positioning of the copper center on
the preferred substrate of AA13 PMOs. The dissociation of the distal
ligand results in the bending of the T-shaped core of the Cu(II) active
site, which could help facilitate its reduction to the active Cu(I)
state. In the Cu(I) state, the G89 loop is in the “closed”
conformation with a confined copper center, which could allow for
efficient O2 binding. In addition, the G89 loop remains
in the “closed” conformation in the Cu(II)-superoxo
intermediate, which could prevent off-pathway superoxide release via
exchange with the distal aqueous ligand. Finally, at the end of the
reaction cycle, aqueous ligand binding to the distal site could switch
the G89 loop to the “open” conformation and facilitate
product release
Distal Hydrophobic Loop Modulates the Copper Active Site and Reaction of AA13 Polysaccharide Monooxygenases
Polysaccharide
monooxygenases (PMOs) use a type-2 copper
center
to activate O2 for the selective hydroxylation of one of
the two C–H bonds of glycosidic linkages. Our electron paramagnetic
resonance (EPR) analysis and molecular dynamics (MD) simulations suggest
the unprecedented dynamic roles of the loop containing the residue
G89 (G89 loop) on the active site structure and reaction cycle of
starch-active PMOs (AA13 PMOs). In the Cu(II) state, the G89 loop
could switch between an “open” and “closed”
conformation, which is associated with the binding and dissociation
of an aqueous ligand in the distal site, respectively. The conformation
of the G89 loop influences the positioning of the copper center on
the preferred substrate of AA13 PMOs. The dissociation of the distal
ligand results in the bending of the T-shaped core of the Cu(II) active
site, which could help facilitate its reduction to the active Cu(I)
state. In the Cu(I) state, the G89 loop is in the “closed”
conformation with a confined copper center, which could allow for
efficient O2 binding. In addition, the G89 loop remains
in the “closed” conformation in the Cu(II)-superoxo
intermediate, which could prevent off-pathway superoxide release via
exchange with the distal aqueous ligand. Finally, at the end of the
reaction cycle, aqueous ligand binding to the distal site could switch
the G89 loop to the “open” conformation and facilitate
product release
Modification of the Adhesive Properties of Silicone-Based Coatings by Block Copolymers
The improvement of the (bio)adhesive
properties of elastomeric
polydimethylsiloxane (PDMS) coatings is reported. This is achieved
by a surface modification consisting of the incorporation of block
copolymers containing a PDMS block and a poly(2-(dimethylamino)ethyl
methacrylate) (PDMAEMA) block in a PDMS matrix, followed by matrix
cross-linking and immersion of the obtained materials in water. Contact
angle measurements (CA), X-ray photoelectron spectroscopy (XPS), and
atomic force microscopy (AFM) showed the presence of the PDMAEMA block
at the surface, drastic morphology changes, and improved adhesion
properties after immersion in water. Finally, underwater bioadhesion
tests show that mussels adhere only to block copolymer-filled coatings
and after immersion in water, i.e., when the PDMAEMA blocks have been
brought to the coating surface. These observations highlight the significant
role of hydrophilic groups in the surface modification of silicone
coatings