[Comparative bacteriostatic and bactericidal activities of mezlocillin against Listeria (author's transl)]

The bacteriostatic activity of mezlocillin was compared with those of benzylpenicillin, ampicillin, amoxicillin, carbenicillin and cephalothin against 197 strains of Listeria monocytogenes, including 18 laboratory strains belonging to various serotypes. The most active antibiotics were benzylpenicillin and amoxycillin (0.25 micrograms/ml inhibited 100% of the strains), followed by ampicillin (0.5 micrograms/ml); 98% of the strains were inhibited by mezlocillin 1 micrograms/ml. The bactericidal activity of mezlocillin was compared with that of ampicillin against 10 strains of Listeria. After 6 or 24 hours of incubation, the antibiotics had weak bactericidal activities. After 48 hours, MICs and MBCs were almost identical. The bactericidal activity of mezlocillin was one dilution greater than that of ampicillin.