Chemical naturebeta-lactam antibiotic
SpectrumBroad-spectrum (effective against both gram-positive and gram-negative bacteria 
Antibacterial effectBactericidal, Only kills multiplying bacteria
TargetPenicillin-binding proteins (PBP)
Mode of actionInhibition in the cross-linkage of peptidoglycan
Mode of resistance (resistance gene in plasmid vectors)β-lactamase gene (ampicillin hydrolysis before ampicillin enters the cell) 
OriginSemi-synthetic derivative of penicillin
Amphoteric compound (can react with both acid and base) (Hill et al., 1975)
  • Ampicillin belongs to a group of beta-lactam antibiotics. It is classified as critically important human medicine by WHO.Ampicillin
  • Ampicillin is used to treat many different types of bacterial infections including bladder infections, ear infections, gonorrhea, pneumonia, and E. coli and salmonella infection.
  • Ampicillin is one of the synthetic derivatives of penicillin. It was generated by adding an amino group side chain on penicillin.
  • In contrast to penicillin which is primarily active against gram-positive bacteria, ampicillin is active against both gram-positive and gram-negative bacteria.
  • Ampicillin inhibits the synthesis of the bacterial cell wall by stopping the peptidoglycan cross-linking.
  • Ampicillin functions as a competitive inhibitor of the enzyme transpeptidase which is required for the synthesis of the bacterial cell wall.
  • Due to the inhibition of cell wall synthesis, bacteria do not grow and have a risk to die due to lysis in the presence of ampicillin. However, as the ampicillin concentration decreases below the critical level in the surroundings, live bacteria resume cell wall synthesis and growth.
  • Ampicillin is one of the most extensively used antibiotics as a selection marker in molecular biology and bacteriology. Many commonly used vectors have an ampicillin resistance gene.
  • Commercially ampicillin is available in 3 forms: Ampicillin anhydrous, Ampicillin trihydrate, and Ampicillin sodium salt.
PropertyAmpicillin anhydrousAmpicillin trihydrateAmpicillin sodium salt
CAS Number69-53-4 7177-48-2 69-52-3 
Molecular formulaC16H19N3O4 C16H19N3O4S.3H2C16H18N3O4Na 
Molecular weight349.4 403.4 371.4


  • Hill et al., 1975. Dissolution and bioavailability of the anhydrate and trihydrate forms of ampicillin. J Pharm Pharmacol. 27(8), 594-598. PMID-239175; Full Text Link: oup, docksci

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