Publisher's Synopsis
All penicillins function by activating other enzymes that tear down the protective wall of the microbe, and by blocking the enzymes responsible for cell wall formation in bacteria that are multiplying. They only work on bacteria that are actively multiplying and making new cell walls, and they have no impact on human cells as a result (which fundamentally lack cell walls).
Staphylococcus aureus, which was once susceptible to penicillin, has developed a specific resistance to the naturally occurring penicillins. This resistance can take the form of either the production of -lactamase (penicillinase), an enzyme that disrupts the internal structure of penicillin and thus destroys its antimicrobial action, or the absence of cell wall receptors for penicillin, greatly reducing the ability of the drug to enter bacterial cells. Because of this, penicillins that are resistant to penicillinase have been developed (second-generation penicillins). Even though they are resistant to -lactamase, these medicines are not as efficient against Staphylococcus as the natural penicillins and have a higher risk of liver damage. Methicillin-resistant Staphylococcus aureus is one type of Staphylococcus that has evolved resistance to penicillinase-resistant penicillins (MRSA).
