Ampicillin (ATC Code J01CA01) is a broad-spectrum bactericidal aminopenicillin antibiotic that inhibits bacterial cell wall mucopeptide synthesis by binding irreversibly to Penicillin-Binding Proteins (PBPs 1A, 1B, and 3), triggering autolysin-mediated osmotic bacteriolysis.
Antimicrobial Spectrum & Clinical Indications
Because of its free amino group, Ampicillin penetrates the outer membrane porin channels of Gram-negative bacilli more effectively than benzylpenicillin (Penicillin G). Primary clinical indications include:
- Enterococcal Infections: Drug of choice for susceptible Enterococcus faecalis urinary tract infections (UTIs), endocarditis (in synergistic combination with gentamicin or ceftriaxone), and bacteremia.
- Listeria monocytogenes Meningitis & Sepsis: First-line intravenous therapy (2 g IV every 4 hours) for neonatal, maternal, and immunocompromised central nervous system listeriosis.
- Respiratory & Gastrointestinal Infections: Non-beta-lactamase-producing Haemophilus influenzae, Streptococcus pneumoniae, Proteus mirabilis, and Salmonella / Shigella species.
Resistance Mechanisms & Beta-Lactamase Combination (Ampicillin-Sulbactam)
Plasmid-mediated TEM-1 and SHV-1 beta-lactamases hydrolyze the beta-lactam ring of standalone ampicillin in up to 50–65% of community Escherichia coli isolates. Pairing ampicillin with the irreversible beta-lactamase inhibitor Sulbactam (Unasyn) restores activity against beta-lactamase-producing Staphylococcus aureus, H. influenzae, Bacteroides fragilis, and Acinetobacter baumannii.
• Urine Culture & Antimicrobial Susceptibility (ABST) Clinical Guide
• Urinary Tract Infection (UTI) Treatment Guidelines