Bleeding management in computed tomography-guided liver biopsies by biopsy tract plugging with gelatin sponge slurry.

To evaluate the safety and impact of biopsy tract plugging with gelatin sponge slurry in percutaneous liver biopsy. 300 consecutive patients (158 females, 142 males; median age, 63 years) who underwent computed tomography-guided core biopsy of the liver in coaxial technique (16/18 Gauge) with and without biopsy tract plugging were retrospectively reviewed (January 2013 to May 2018). Complications were rated according to the common criteria for adverse events (NCI-CTCAE). The study cohort was dichotomized into a plugged (71%; n = 214) and an unplugged (29%; n = 86) biopsy tract group. Biopsy tract plugging with gelatin sponge slurry was technically successful in all cases. Major bleeding events were only observed in the unplugged group (0.7%; n = 2), whereas minor bleedings (4.3%) were observed in both groups (plugged, 3.6%, n = 11; unplugged, 0.7%, n = 2). Analysis of biopsies and adverse events showed a significant association between number of needle-passes and overall (P = 0.038; odds ratio: 1.395) as well as minor bleeding events (P = 0.020; odds ratio: 1.501). No complications associated with gelatin sponge slurry were observed. Biopsy tract plugging with gelatin sponge slurry is a technically easy and safe procedure that can prevent major bleeding events following liver biopsy.

Structural dynamics of the cell wall precursor lipid II in the presence and absence of the lantibiotic nisin.

Representing a physiological "Achilles' heel", the cell wall precursor lipid II (LII) is a prime target for various classes of antibiotics. Over the years LII-binding agents have been recognized as promising candidates and templates in the search for new antibacterial compounds to complement or replace existing drugs. To elucidate the molecular structural basis underlying LII functional mechanism and to better understand if and how lantibiotic binding alters the molecular behavior of LII, we performed molecular dynamics (MD) simulations of phospholipid membrane-embedded LII in the absence and presence of the LII-binding lantibiotic nisin. In a series of 2×4 independent, unbiased 100ns MD simulations we sampled the conformational dynamics of nine LII as well as nine LII-nisin complexes embedded in an aqueous 150mM NaCl/POPC phospholipid membrane environment. We found that nisin binding to LII induces a reduction of LII mobility and flexibility, an outward shift of the LII pentapeptide, an inward movement of the LII disaccharide section, and an overall deeper insertion of the LII tail group into the membrane. The latter effect might indicate an initial step in adopting a stabilizing, scaffold-like structure in the process of nisin-induced membrane leakage. At the same time nisin conformation and LII interaction remain similar to the 1WCO LII-nisin NMR solution structure.

Efflux pump-mediated antibiotics resistance: insights from computational structural biology.

The continuous rise of bacterial resistance against formerly effective pharmaceuticals is a major challenge for biomedical research. Since the first computational studies published seven years ago the simulation-based investigation of antibiotics resistance mediated by multidrug efflux pumps of the resistance nodulation division (RND) protein super family has grown into a vivid field of research. Here we review the employment of molecular dynamics computer simulations to investigate RND efflux pumps focusing on our group's recent contributions to this field studying questions of energy conversion and substrate transport in the inner membrane antiporter AcrB in Escherichia coli as well as access regulation and gating mechanism in the outer membrane efflux ducts TolC and OprM in E. coli and Pseudomonas aeruginosa.

Unilateral access regulation: ground state dynamics of the Pseudomonas aeruginosa outer membrane efflux duct OprM.

Acting as an efflux duct in the MexA-MexB-OprM multidrug efflux pump, OprM plays a major role in the antibiotic resistance capability of Pseudomonas aeruginosa, trafficking substrates through the outer cell membrane. Whereas the available crystal structures showed restricted OprM access on both ends, the underlying gating mechanism is not yet fully understood. To gain insight into the functional mechanism of OprM access regulation, we conducted a series of five independent, unbiased molecular dynamics simulations, computing 200 ns dynamics samples of the wild-type protein in a phospholipid membrane/150 mM NaCl water environment. On the extracellular side, OprM opens and closes freely under the simulated conditions, suggesting the absence of a gating mechanism on this side of the isolated protein. On the periplasmic side, we observe an opening of the tip regions at Val408 and to a lesser degree Asp416 located 1.5 nm further into the channel, leading to OprM end conformations being up to 3 and 1.4 times, respectively, more open than the asymmetric crystal structure. If our simulations are correct, our findings imply that periplasmic gating involves only the Asp416 region and that in vivo additional components, absent in our simulation, might be required for periplasmic gating if the observed opening trend near Asp416 is not negligible. In addition to that ,we identified in each monomer a previously unreported sodium binding site in the channel interior coordinated by Asp171 and Asp230 whose functional role remains to be investigated.