Impetigo comes from a bacterium known as staphylococcus aureus. Cefalexin does not treat methicillin-resistant "Staphylococcus aureus" infections. For Methicillin-resistant Staphylococcus aureus (MRSA), vancomycin or teicoplanin is recommended. Such organisms include methicillin-resistant "Staphylococcus aureus" (MRSA). Vancomycin is used if infection with methicillin-resistant "Staphylococcus aureus" (MRSA) is suspected. The bacteria most commonly involved are streptococci and "Staphylococcus aureus". Infections resulting in bacteremia from "Staphylococcus aureus" require removal of the catheter and antibiotics. However, it is ineffective against methicillin-resistant Staphylococcus aureus (MRSA). Infection is usually caused by "Staphylococcus aureus". It is also useful in the treatment of superficial methicillin-resistant "Staphylococcus aureus" (MRSA) infections. It is not active against methicillin-resistant "Staphylococcus aureus". Cefalexin is not effective against infections caused by methicillin-resistant "Staphylococcus aureus" (MRSA), "Enterococcus", or "Pseudomonas". It is not effective for methicillin-resistant "Staphylococcus aureus" (MRSA). It is typically due to either "Staphylococcus aureus" or "Streptococcus pyogenes". It is also under research as an bactericidal agent against "Escherichia coli" and "Staphylococcus aureus".