You have isolated a Staphylococcus aureus from a superficial wound swab from a community patient. What antibiotics do you need to test against?
If you are fortunate enough to have Automated Susceptibility testing (Vitek, Phoenix etc) you may test the isolate against a panel of 20 different Gram positive antibiotics at a not unsignificant cost. You will also be testing against a lot of antibiotics that are never going to be used to treat that patient.
If you perform anti-microbial susceptibility testing mainly by disc diffusion on agar plate, then you will likely test the Staphylococcus aureus against 6 or 7 antibiotics of your choosing. Again, in the vast majority of patients, some of these antibiotics will neither be reported nor used.
In the laboratory I work in, we cut the number of antibiotics routinely tested for a Staphylococcus aureus isolate from six to three, of which we routinely report two of them to the clinicians. In the three years that we have had this policy we have not had one negative comment from our laboratory users. (On occasion of course we do test more, ie MRSA isolate, patient with multiple allergies.)
It made me realise just how much susceptibility testing that we do on a “Just in Case” basis, not only for Staphylococcus aureus, but also for a multitude of other micr-organisms also.
It will be very interesting if MALDI-TOF technology becomes proficient at identifying MRSA in the future. If this happens, then (if no history of allergy on the request form), one could simply put out a report saying: “Staphylococcus aureus isolated, (not MRSA). Susceptibilities on request.”
A radical, but ultimately reasonable and cost-effective approach, which I am sure would be accepted by laboratory users…