MODEL RELEASED. Staphylococcus bacteria research. Bacteriologist holding petri dishes containing Staphylococcus sp. bacteria. This bacterium is usually harmless as it is found naturally on the skin and mucous membranes of humans and many animals. However, it can cause infections if it comes into contact with broken skin and can cause food poisoning if ingested. Some strains have also developed wide ranging antibiotic resistance, such as methicillin-resistant S. aureus (MRSA). MRSA is a dangerous hospital pathogen, as it can infect post-surgery wounds and cause pneumonia to develop in those with weakened immune systems. Photographed at St. Mary's Hospital in Lacor, Gulu, Uganda.