How to bold mismatched parts?

There is a database of links, we insert a link in the search database, for example and search gives the following results:

how to make so that the output is shown here:
April 4th 20 at 00:59
2 answers
April 4th 20 at 01:01
look at the task differently: allocate each result – search string. And the rest make bold )

Help easy to replace str_replace(), or if possible multiple occurrence of the search fragment in the string, preg_replace().

To replace the search string it the same in the wrapper, for example, the tags <span>search string</span>. Gimoto/airnote to make styles.
April 4th 20 at 01:03

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