Susceptibility and analysis of resistance to β-lactum agents of Enterobacteriaceae detected in blood cultures

Abstract

We studied resistance to β-lactum agents in 329 strains of Enterobacteriaceae detected in blood cultures in the 10 years between 1991 and 2000. Drug sensitivity tests showed good sensitivity (MIC₉₀:≤0.5g/mL) in third-generation cephem and in carbapenem to Escherichia coli and Klebsiella pneumoniae. We found relatively good sensitivity of fourth-generation cephem (the sensitivity of third-generation cephem was slightly lower) and carbapenem to Enterobacter cloacae, Citrobacter freundii, and Serratia marcescens. For all Enterobacteriaceae, meropenem was the lowest (MIC₉₀:≤0.12μg/mL). Resistance among bacterial species using ceftazidime was the highest in E. cloacae (50.5%). Double-disk synergy tests (DDST) were positive in 19 strains and 2-mercapto propionic acid tests (2-MP) were positive in 5 strains. As resistance genes, the extended spectrum β-lactamase (ESBL)-producing gene, CTX-M 1/3, was detected in 18 of 19 strains. The metallo β-lactamase (MBL)-producing gene was detected in 5 strains which were IMP-1. In K. pneumoniae detected in 1991, the presence of SHV ESBL-producing bacteria was confirmed. A clinical background survey showed a high incidence of serious conditions such as malignant tumors and cerebrovascular diseases as underlying diseases, and IVH catheters had been inserted in all patients. Clinical symptoms were improved after administration of carbapenem and aminoglycosides in patients with ESBL-producing bacteria infection, and by administration of aztreonam in patients with MBL-producing bacteria infection.