In vitro Activities of Mecillinam Against Clinical Isolates of Enterobacteriaceae

Background : Mecillinam, an amidinopenicillin antibiotic, has been used to treat urinary tract infections and bacterial enteritis in many countries. In this study, we evaluated in vitro activity of mecillinam against Enterobacteriaceae isolates from urine, and Salmonella and Shigella isolates from patients with bacterial gastroenteritis. Materials and Methods : A total of 308 clinical strains were collected and were comprised of Escherichia coli (n=109), Klebsiella pneumoniae (n=52), Enterobacter spp. (n=30), Serratia marcescens (n=30) and Proteus spp. (n= 29) isolated from a university hospital in Korea in 2007, and of Salmonella spp. (n= 28) and Shigella spp. (n= 30) isolated from Korean diarrheal patients from 2001 to 2006. Antimicrobial susceptibility was tested by Clinical Laboratory Standard Institute (CLSI) agar dilution method. CLSI breakpoint of mecillinam for E. coli urinary tract isolates was applied to all other isolates. Results : In E. coli, rate of susceptibility to ampicillin was 30%, but 99-100% to amikacin and cefotaxime. Most (96%) of E. coli isolates, including extended-spectrum beta-lactamase (ESBL) producers, were susceptible to mecillinam. All ESBL producers, except for one isolate, were inhibited by <= 4 mu g/mL of mecillinam. MIC90 of mecillinam for K. pneumoniae and Enterobacter spp. was 8 mu g/mL and 1 mu g/mL, respectively, and the susceptibility rate was 92% and 97%, respectively. However, MIC90 of mecillinam for S. marcescens isolates was >128 mu g/mL and most of them were resistant to mecillinam. All Salmonella isolates and 27 of 30 Shigella isolates were susceptible to mecillinam. Conclusion : Mecillinam was active in vitro against most Enterobacteriaceae, Salmonella, and Shigella isolates except for S. marcescens. Therefore, mecillinam can be a good alternative agent for treating urinary tract infection and bacterial gastroenteritis.