Hello and welcome to healthcare forum.
Cause of ineffectivity of any antibiotic is resistance of microorganism to that antibiotic.
So, before starting any antibiotic go for swab culture and sensitivity test which will identify the infecting microorganism as well suggest proper antibiotic for its treatment.
By this way every infection, including staph is treatable.
I hope i have answered your query.
Best wishes for your health.
staph is very common and smart bacteria.
it learn to resist antibiotic very fast.
many antibiotic are there in market.
but many of them do not work as there is resistant develop by bacteria
so now a day ,it is advisable to do sensitivity test and then take proper medicine
if minor infection is there ,it cover by penicillin group of drug mainly,
if skin infection is there ,u need to apply mupirocin cream over it