Ampicillin

Ampicillin is a beta-lactam antibiotic that has been used extensively to treat bacterial infections since 1961. It is considered part of the aminopenicillin family and is roughly equivalent to amoxicillin in terms of spectrum and level of activity. It can sometimes result in allergic reactions that range in severity from a rash (e.g. patients with mononucleosis) to potentially lethal anaphylaxis.

Mechanism of action
Belonging to the penicillin group of beta-lactam antibiotics, ampicillin is able to penetrate Gram-positive and some Gram-negative bacteria. It differs from penicillin only by the presence of an amino group. The amino group helps the drug penetrate the outer membrane of gram-negative bacteria. Ampicillin acts as a competitive inhibitor of the enzyme transpeptidase. Transpeptidase is needed by bacteria to make their cell walls. It inhibits the third and final stage of bacterial cell wall synthesis, which ultimately leads to cell lysis.

Indications
Ampicillin is closely related to amoxicillin, another type of penicillin, and both are used to treat urinary tract infections, otitis media, uncomplicated community-acquired pneumonia, Haemophilus influenzae, salmonellosis and Listeria meningitis. It is used with flucloxacillin in the combination antibiotic co-fluampicil for empiric treatment of cellulitis; providing cover against Group A streptococcal infection whilst the flucloxacillin acts against the Staphylococcus aureus bacterium. Of concern is the number of bacteria that become resistant to Ampicillin necessitating combination therapy or use of other antibiotics.

All Pseudomonas and most strains of Klebsiella and Aerobacter are considered resistant.

Use in research
Ampicillin is often used in molecular biology as a test for the uptake of genes (e.g., by plasmids) by bacteria (e.g., E. coli). A gene that is to be inserted into a bacterium is coupled to a gene coding for an ampicillin resistance (in E. coli, usually the bla gene, coding for β-lactamase). The treated bacteria are then grown on a medium containing ampicillin. Only the bacteria that successfully take up the desired genes become ampicillin resistant, and therefore contain the other desired gene as well.