pneumonia

EuroPneumo Special Issue / pneumonia 2015 Oct 21;7:I–72
2. Silva-Martín N, Retamosa MG, Maestro B, Bartual SG, Rodes MJ, García P, Sanz JM, Hermoso JA. Crystal structures of CbpF
complexed with atropine and ipratropium reveal clues for the design of novel antimicrobials against Streptococcus pneumoniae.
Biochim. Biophys. Acta 2014; 1840, 129-135
O3.3
Identification of new cell wall biogenesis factors in Streptococcus
pneumoniae using Tn-Seq
Andrew Fenton, Thomas Bernhardt, David Rudner
Harvard Medical School, Boston, Massachusetts, USA
The bacterial cell wall represents the best clinically validated target for antimicrobials against Streptococcus pneumoniae.
The main enzymes that build the cell wall are synthases belonging to the family of factors called penicillin-binding
proteins (PBPs), which are the targets of penicillin and related beta-lactam drugs. Resistance to the beta-lactams is on
the rise in S. pneumoniae, necessitating the discovery of new antibiotics to treat pneumococcal infections. One attractive
avenue towards this goal is to identify new weak points in the cell wall assembly pathway that can be exploited for the
development of novel therapeutics. Identification of these vulnerabilities will require a more thorough understanding
of cell wall biogenesis, especially with regard to how the process is regulated. Importantly, although the structure and
activity of the PBPs have been studied for decades, surprisingly little is known about how these enzymes are controlled
in vivo. To address this issue, we have used Tn-Seq to identify genetic interactions with a subset of the major synthetic
PBPs in S. pneumoniae. Our analysis has uncovered a novel regulatory factor which plays an essential role in controlling
the cell wall synthetic machinery required for cell division in pneumococci. The discovery of this factor and an analysis
of its activity will be discussed along with the implications for drug discovery.
O3.4
Engineered liposomes sequester pneumolysin and protect from severe
invasive pneumococcal disease in mice
Daniel Neill 1 , Suzanna Gore 1 , Laura Bricio Moreno 1 , Eduard Babiychuk 2 , Aras Kadioglu 1
1
University of Liverpool, Liverpool, UK, 2 University of Bern, Bern, Switzerland
Pneumolysin is a cholesterol-dependent cytolysin which forms pores in the membrane of eukaryotic cells leading to
cellular death. Artificially created liposomes with high concentrations of lipids can be used as decoy targets to sequester
bacterial membrane-damaging toxins, such as pneumolysin. It was observed that in the presence of cholesterol-containing
liposomes, epithelial and endothelial cells were protected against pneumolysin-induced cell lysis. Liposomes were also
able to reduce pneumolysin-induced CXCL8 in HUVEC endothelial cells. In an in vivo model of invasive pneumococcal
disease liposomes were able to increase the survival of mice infected with D39 after a single dose of liposome, which
also reduced the bacterial load in lungs and blood at 24 hours post-infection. During a sepsis in vivo model where
mice infected with D39 typically die 33 hours post-infection, liposomes were able to protect against bacteraemia when
administered 6 or 10 hours post-infection, but not when administered 16 hours post-infection. Liposomes were also
able to reduce bacterial load and levels of TNF-α and pro-inflammatory recruitment of polymorphonuclear leukocytes
in blood. Antibiotic treatment against pneumococci can lead to release of pneumolysin due to bacterial lysis, with
substantial pro-inflammatory and pathogenic consequences to the host. A combination of antibiotic and liposomal toxinsequestration
treatment increased the survival of mice infected with D39 when compared to antibiotic only treated
groups, suggesting that adjunct therapy with liposomes could be a highly effective treatment against infections caused
by pathogens producing cholesterol-dependent cytotoxins.
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