Pirbenicillin

Pirbenicillin exhibits antibacterial activity against 43 clinical isolates of Pseudomonas aeruginosa and 1 strain of Pseudomonas fluorescens^[1].
Pirbenicillin (0.5-64 μg/mL; 1 h) induces concentration-dependent morphological changes in Ampicillin (HY-B0522)-sensitive Escherichia coli ECSA 1, forming filamentous bacteria at low concentrations and spheroplasts and lysis-related morphologies at high concentrations^[1].
Pirbenicillin (2-128 μg/mL; 1 h) inhibits bacterial division and induces filamentation in Pseudomonas aeruginosa^[1].
Pirbenicillin (250 μg/mL; 20 h observation) induces lysis and sustained growth inhibition in 3 partially Ampicillin-sensitive E. coli strains, whereas it causes no obvious changes in the growth curves of 6 Klebsiella strains and 3 highly Ampicillin-tolerant E. coli strains^[1].
Pirbenicillin has MIC₅₀ and MIC₉₀ values of 12.5 and 25 μg/mL in BHI agar and 7.8 and 15.6 μg/mL in BHI broth against Carbenicillin (HY-B0525)-susceptible P. aeruginosa, and MIC₅₀ and MIC₉₀ values of 50 and 200 μg/mL in BHI agar against Carbenicillin-resistant strains^[2].
Pirbenicillin shows an MIC₅₀ of 3.12 μg/mL against 29 strains of Streptococcus faecalis, with the same concentration inhibiting all strains^[2].
When Pirbenicillin is used in combination with Gentamicin (HY-A0276A), the combined MIC of both components in 7 sensitive or resistant P. aeruginosa strains decreases to one-quarter or less of the MIC of each agent alone, demonstrating synergistic antibacterial activity^[2].