Not all antibiotics work equally well against the same germ — and knowing which germ you're dealing with is the first step to finding out which one does. In this experiment, colonies grown from hand swabs are gram stained to confirm they are coagulase-negative staphylococcus before antibiotic testing begins. That identification step matters: when you spread bacteria onto Mueller Hinton plates and place antibiotic discs on each one, the death zones you measure afterward only mean something if the species is consistent across plates. Without confirming the bacterial type first, the sensitivity results could reflect a random mix of germs rather than one known species.