Antimicrobial resistance (AMR) is a major threat to global health. Understanding the emergence, evolution, and transmission of individual antibiotic resistance genes (ARGs) is essential to develop sustainable strategies combatting this threat. Here, we use metagenomic sequencing to analyse ARGs in 757 sewage samples from 243 cities in 101 countries, collected from 2016 to 2019. We find regional patterns in resistomes, and these differ between subsets corresponding to drug classes and are partly driven by taxonomic variation. The genetic environments of 49 common ARGs are highly diverse, with most common ARGs carried by multiple distinct genomic contexts globally and sometimes on plasmids. Analysis of flanking sequence revealed ARG-specific patterns of dispersal limitation and global transmission. Our data furthermore suggest certain geographies are more prone to transmission events and should receive additional attention.

Endodontic treatment of immature teeth is often complicated because of flaring root canals and open apices for which apexification is needed. Long-term prognosis for these teeth is surprisingly low because of cervical root fractures occurring after an impact of weak forces. In this study, an experimental model was developed to determine the fracture resistance of immature teeth and to test the hypothesis that endodontic materials succeed in reinforcing them. Compact and hollow bone cylinders from bovine femurs were used as standardized samples. In order to evaluate the experimental model, fracture resistance in both groups was evaluated by determining the ultimate force to fracture (UFF) under diametral tensile stress. Analysis of variance (ANOVA) revealed a statistically significant difference between the mean values of UFF for both groups, independently of the sampling location or subject. In a following setting, the hypothesis that obturation with gutta percha (GP), mineral trioxide aggregate (MTA), or calcium phosphate bone cement (CPBC) reinforces the hollow bone samples was investigated. Obturation resulted in a significant reinforcement for all materials, but the degree of reinforcement depended on the material. The experimental model appeared to be suitable for in vitro investigation of reinforcement and fracture resistance in a standardized way.

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In this study the composition of K + -and CO 3 2--containing hydroxyapatites (KCAp's) obtained by the hydrolysis of octacalcium phosphate (OCP), Ca 8 (HPO 4 ) 2 (PO 4 ) 4 ‚5H 2 O, was investigated as a function of the carbonate concentration c kc and the molar K/CO 3 ratio R of the aqueous solution. OCP was hydrolyzed at 95 °C in K +and CO 3 2--containing solutions with 2.5 e c kc (mM) e 100 and 2 e R e 20. Physical and chemical analyses showed that the precipitates were carbonated apatites with a carbonate content ranging from 2.5 to 5.5 wt %. The samples also contained a significant amount of monohydrogen phosphate (1.3-2.2 wt %) and an appreciable amount of water (3.5-5.5 wt %) after drying at 25 °C under vacuum. The chemical composition of the KCAp's can be explained by the occurrence of a main substitution mechanism [I: Ca 2+ + PO 4 3-+ OH -T V Ca + CO 3 2-+ V OH ] and a coupled K + and CO 3 2incorporation [III: Ca 2+ + PO 4 3-T K + + CO 3 2-] where V X stands for a vacancy in the X sublattice. The relative contribution of mechanism III with respect to mechanism I increases with increasing c kc and R.

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