Pencillins (from the family ofbeta-lactam antibiotics) work by preventing the peptidoglycan cross liking of bacterial cell walls by binding to the enzyme DD-transpeptidase. Some bacteria have developed resistance to these now by producing beta-lactamase - which breaks down the DD-transpeptidase causing it to be ineffective. This ability has spread though the mixing of bacterial genes, which occurs though a number of mechanisms including gene transfer and 'picking up' genes from lysed cells.
