Is there any way to change the style of part of an axis title while keep the rest part unchanged? In my case, How could I italicize \"bacteria X\" in the y-axis title? T
I believe RFelber's suggestion is what you are after. Try this:
labs(x="Groups", y=expression('No. of'~italic(bacteria X)~'isolates with corresponding types'), fill="Var1")
I did not need to use the bquote() function. The tildes produce single spaces for terms that are outside of the quotes.
bquote()