Penicillin (whiles abbreviatit PCN or pen) is a group o antibiotics derived frae Penicillium fungi,[1] includin penicillin G, procaine penicillin, benzathine penicillin, an penicillin V.

Penicillin core structur, whaur "R" is the variable group.

Penicillin antibiotics are historically signeeficant acause thay are the first drugs that wur effective against mony previously serious diseases, such as syphilis, an infections caused bi staphylococci an streptococci. Penicillins are still widely uised the day, tho mony types o bacteria hae nou acome resistant. Aw penicillins are β-lactam antibiotics an are uised in the treatment o bacterial infections caused bi susceptible, uisually Gram-positive, organisms.