Hi @Microbio,
I am not in the Biosciences field, but I believe that this should apply to any field. Having publications, in general, is a really good thing if you are applying to a Ph.D. program at any university since it shows that you have had concrete research experience in the past. I don't think that changing your research focus for your Ph.D. would be a problem, but you should provide the university with an explanation of why you want to change your focus area. This can be done when writing your statement of purpose. I believe that all of the skills that you have learned in the other field within biology are somehow transferable to this new field, so it should still have a positive impact in your application.
Hope this helps.
