Cefsulodin is a β-lactam antibiotic that lyses actively-growingE. coliby binding specifically to the intermembrane proteins, penicillin-binding proteins 1a and b, whose transglycosylase and transpeptidase activities are involved in cell elongation and septation.1Cefsulodin has been used in combination with other β-lactam antibiotics, such as cefazolin as a strategy to circumvent drug resistance.2