Antibiotic resistant bacteria. Petri dish culture of antibiotic resistant Staphylococcus aureus bacteria. The bacteria have been plated (streaked) across an agar growth medium, and are seen growing as white colonies. Staphylococcus aureus is a Gram-positive spherical (coccus) bacteria. It is found on healthy skin and mucous membranes, such as the lining of the mouth. But S. aureus may also cause boils, internal abcesses and food poisoning. The strain cultured here is especially dangerous as it has developed resistance to all known antibiotic drugs and is therefore untreatable. Photographed at Magainin Pharmaceuticals, Pennsylvania, USA.