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Bacillus cereus is an endemic, soil-dwelling, Gram-positive, rod-shaped, beta hemolytic bacterium. Some strains are harmful to humans and cause foodborne illness, while other strains can be beneficial as probiotics for animals. It is the cause of "Fried Rice Syndrome". B. cereus bacteria are aerobes, and like other members of the genus Bacillus can produce protective endospores.
Staphylococcus epidermidis is one of thirty-three known species belonging to the genus Staphylococcus. It is part of our skin flora(commensal), and consequently part of human flora. It can also be found in the mucous membranes and in animals. Due to contamination, it is probably the most common species found in laboratory tests.
Although S. epidermidis is not usually pathogenic, patients with a compromised immune system are often at risk for developing an infection. These infections can be both nosocomial or community acquired, but they are more of a threat to hospital patients. This is related to hospitals carrying more virulent strains of the organism, due to continuous use of antibiotics and disinfectants.
S. epidermidis is also a major concern for people with catheters or other surgical implants because it is known to cause biofilms that grow on these devices.