Antimicrobial susceptibility of Serratia marcescens isolated from clinical materials

This study was undertaken to determine the source, serological characteristics and susceptibility to the chemotherapeutic agents on recently isolated strains of Serratia marcescens. Of the 351 isolates, the most frequent source was the respiratory tract and the second urinary tract. The most common serotype was type 14 and the second 4. Among the types of S. marcescens, type 14 and 4 were most frequently associated with respiratory infections. The strains from infected urine had common types 14, 4 and 14.12. By the disk sensitivity testing, the strains from urine had a tendency of multiple resistance and the strains type 14.12 also had the same tendency. In vitro tests for susceptibility to 16 chemotherapeutic agents were performed. Norfloxacin and ofloxacin were most active drugs and inhibited about 70% of the strains at a concentration of 0.39 microgram and 0.78 microgram or less per ml, respectively. The new cephalosporins (cefmenoxime, ceftizoxime and latamoxef) and aztreonam inhibited from 76 to 86% of the strains at 6.25 micrograms or less per ml. This was comparable to the percentage inhibited by some aminoglycosides (gentamicin, tobramycin, amikacin and sisomicin) ranging from 60 to 80%. Minocycline and nalidixic acid were moderate in activity. Chloramphenicol was less active.