404. That’s an error.
The requested URL /bookmarks/mark?op=add&bkmk=http%3A//science.sciencemag.org/content/138/3542/828&title=Electron%20Microscopy%20of%20Staphylococcus%20aureus%20Treated%20with%20Tetracycline
was not found on this server. That’s all we know.