Does a change of articles "reset" the item count when it comes to serial commas? For instance, if using the serial comma, does the statement "I am the author of the book XYZ, a presenter and teacher," require a comma after presenter, or does the change in article reset the number of items to two? I don't have a specific reason why it would, but in writing a similar sentence it struck me as a possibility.
In order to maintain parallel structure in your sentence, you would repeat the article, like this:
I am the author of the book XYZ, a presenter, and a teacher.
Personally, I prefer the serial comma but it is considered a style choice. You could omit the comma there and the sentence would still be clear. You would still need the article for parallel structure though:
I am the author of the book XYZ, a presenter and a teacher.