@sunnychu, welcome to Keyboard Maestro (KM) and its Forum.
KM is one of the best Mac automation tools available, its Forum is one of the best and friendliest forums on the Internet. Whenever you reach a tough stumbling block trying to use KM, please feel free to post your question/problem here for help.
I don't know if this is your actual, real-world use case, but if it is then I'd suggest that you use a grammar checker rather than KM.
For example, it is much more complicated to handle:
"This is a very red apple"
But, just for grins, I did write a macro that addresses your specific request:
It offers the following:
KM Variables at the top where you can set the prefix and suffix for each string.
Uses the RegEx metacharacter to match all characters other than vowels.
Below is just an example written in response to your request. You will need to use as an example and/or change to meet your workflow automation needs.