he two natural penicillins obtained

he two natural penicillins obtained from culture filtrates of Penicillium notatum or the closely related species P. chrysogenum are penicillin G (shown in the diagram) and the more acid-resistant penicillin V. They are active only against Gram-positive bacteria (which have a thick layer of peptidoglycan in the wall) and not against Gram-negative species, including many serious pathogens like Mycobacterium tuberculosis (the cause of tuberculosis). (see Gram reaction for further details). Nevertheless, the natural penicillins were extremely valuable for treating wound pathogens such as Staphylococcus in wartime Europe.