Staphylococcus aureus culture. Test-tube containing S. aureus bacteria (white) in a nutrient solution. These Gram-positive cocci (round) bacteria are found on the skin and mucous membranes of humans and many animals. They are usually harmless, but infections can occur on broken skin or within a blocked sweat or sebaceous gland, resulting in boils, pustules and abscesses. S. aureus can also cause food poisoning, producing toxins that induce vomiting. Certain strains cause the potentially fatal toxic shock syndrome (TSS). Some strains have developed wide-ranging antibiotic resistance, such as methicillin- resistant S. aureus (MRSA) and are hospital pathogens.