In gram positive bacteria have a peptidoglycan layer outside of the cell wall. Gram negative bacteria have peptidoglycan between membranes.
The natural penicillin have activity against non beta lactamase producing gram - positive cocci, which includes such as - viridans streptococci, anaerobic streptococcus. Penicillin work indirectly bursting bacteria cell walls. It kills bacteria through binding of that betalactum ring.
Gram positive bacteria have a much thicker layer of peptidoglycan and lack of the protection of an outer membrane. This class , penicillin was first antibiotic to be used widely and prevents the final cross linking step. There are some more classes of penicillin like- natural , penicillin-stable, aminopenicillins and extended-spectrum penicillin.
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