Rabbit Ant-S. aureus PBP2a polyclonal antibody for ELISA, WB. Methicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen responsible for serious hospital infections worldwide. These bacteria are resistant to all beta-lactam antibiotics due to the production of an additional penicillin binding protein, the PBP2a (about 75 kDa) encoded by the mecA gene, which shows low affinity for this class of antibiotics. This enables transpeptidase activity in the presence of betalactams, preventing them from inhibiting cell wall synthesis.