<P> About 10% of people report that they are allergic to penicillin; however, up to 90% of this group may not actually be allergic . Serious allergies only occur in about 0.03% . All penicillins are β - lactam antibiotics . </P> <P> Penicillin was discovered in 1928 by Scottish scientist Alexander Fleming . People began using it to treat infections in 1942 . There are several enhanced penicillin families which are effective against additional bacteria; these include the antistaphylococcal penicillins, aminopenicillins and the antipseudomonal penicillins . They are derived from Penicillium fungi . </P> <P> The term "penicillin" is often used generically to refer to benzylpenicillin (penicillin G, the original penicillin found in 1928), procaine benzylpenicillin (procaine penicillin), benzathine benzylpenicillin (benzathine penicillin), and phenoxymethylpenicillin (penicillin V). Procaine penicillin and benzathine penicillin have the same antibacterial activity as benzylpenicillin but act for a longer period of time . Phenoxymethylpenicillin is less active against gram - negative bacteria than benzylpenicillin . Benzylpenicillin, procaine penicillin and benzathine penicillin can only be given by intravenous or intramuscular injections, but phenoxymethylpenicillin can be given by mouth because of its acidic stability . </P> <P> While the number of penicillin - resistant bacteria is increasing, penicillin can still be used to treat a wide range of infections caused by certain susceptible bacteria, including Streptococci, Staphylococci, Clostridium, Neisseria, and Listeria genera . The following list illustrates minimum inhibitory concentration susceptibility data for a few medically significant bacteria: </P>

When was penicillin widely used for the first time