Introduction There are 6 classic Gram-positive groups of bacteria that cause disease in humans 2 are cocci one of these is Staphylococcus the other is Streptococcus Streptococci vs staphylococcus on Gram stain, strep looks like a "strip" of bacteria, while staph looks like a cluster (shown at right) strep is catalase negative, staph is catalase positive most staph are penicillin G resistant (important to know for treatment!) 3 pathogenic staphylococcus species S. aureus S. epidermidis S. saprophyticus