Great question. Firstly, I am not a lawyer and for anything approaching a formal legal answer you'd need this to be migrated to Law.SE. With that caveat, I'll have a go.
Original content is covered automatically by copyright. Under the 1886 Berne Convention which first established the recognition of copyrights among sovereign nations, copyrights do not have to be asserted or declared, as they are automatically in force at creation: an author need not "register" or "apply for" a copyright in countries adhering to the Berne Convention.
Certain categories of work cannot be copyrighted. For example, a list of the materials required for a protocol cannot be copyrighted, at least under US copyright law (reference). However, the protocol itself can be.
Usage of copyrighted material is permitted under certain conditions, such as fair use. I'll probably expand on this later, but basically while fair use is not clearly defined it could fall within the usage described here.
If you did that, you should make it clear what part of the M&M in your paper is quoted from the source (and clearly attribute it).
For categories of work that are covered by copyright, unless covered by e.g. fair use reroduction of a substantial portion of the work is prohibited by the laws of copyright without a special license.
A free license or open license is a license agreement which contains conditions permitted to the user from the holder on a specific list of uses for his work. As originally defined (and thus with respect to software, which was the original target of these licenses) a license is free if it gives users the following freedoms:
- Freedom 0: The freedom to run the program for any purpose.
- Freedom 1: The freedom to study how the program works, and change it to make it do what you wish.
- Freedom 2: The freedom to redistribute and make copies so you can help your neighbor.
- Freedom 3: The freedom to improve the program, and release your improvements (and modified versions in general) to the public, so that the whole community benefits.
(Freedom 2 is the most relevant for our purposes.)
Licenses meeting these criteria and commonly in use by academic publishers include Creative Commons licenses such as CC-BY-4.0 (which is used by all PLOS journals).
TL;DR: the only way to guarantee you won't get sued for copyright infringement is to target studies published under open licenses, or get explicit permission from the copyright holder.