Antimicrobial susceptibilities of Listeria monocytogenes strains isolated from 1958 to 1982 in Sweden.

Antibiotic susceptibility was studied in 175 clinical isolates of Listeria monocytogenes. There were no major changes in the susceptibility of strains between 1958 and 1982. Benzylpenicillin and ampicillin had MICs for 90% of the strains (MIC90) of 0.5 micrograms/ml. Gentamicin also had good activity against L. monocytogenes, with an MIC90 of 1.0 microgram/ml. All the new beta-lactamase-stable cephalosporins tested had relatively poor activity against L. monocytogenes. Of the bacteriostatic antibiotics, trimethoprim had by far the lowest MIC90 (0.06 microgram/ml), and in combination with sulfamethoxazole (co-trimoxazole), it had an MIC90 of 0.5 microgram/ml. Both erythromycin and doxycycline had low MIC90s (0.25 microgram/ml).