Conjugative Transfer of Multiresistance Plasmids from ESBL−positive Escherichia coli and Klebsiella spp. Clinical Isolates to Escherichia coli Strain K12 C600 Transfer koniugacyjny plazmidów wielooporności z ESBL−dodatnich klinicznych szczepów Escherichia coli i Klebsiella spp. do szczepu Escherichia coli K12 C600

Objectives. The aim of this study was to evaluate the transfer frequency of plasmid−borne genes coding for extend− ed−spectrum β−lactamases (ESBLs) from clinical isolates of E. coli and Klebsiella spp. to the E. coli K12 C600 recipient strain. Additionally, the antimicrobial susceptibility of the donor strains and transconjugants obtained in mating experiments were studied. Material and Methods. A total of 51 ESBL−producing E. coli (n = 32) and Klebsiella spp. (n = 19) clinical strains isolated from children hospitalized in the Medical University Hospital in Wroclaw, Poland, were used in this study. Transfer of plasmids carrying ESBL−encoding genes was performed using the conjugational broth method. ESBL production was detected by the double−disk synergy test (DDST). The minimal inhibitory concentrations (MICs) of antimicrobial drugs were determined by an agar dilution technique on Mueller−Hinton agar. The presence of the blaCTX−M gene in donor strains and transconjugants was determined by PCR. Results. The majority of the isolates studied (92.2%) transferred ESBL−encoding plasmids to the E. coli K12 C600 recipient strain with a frequency of 10 −5 –10 –1 per donor strain. Donor strains and transconjugants displayed resis− tance patterns typical of ESBL producers. They were resistant to cefotaxime, cefrtiaxone, and aztreonam but sus− ceptible to carbapenems and oxyimino−β−lactams (ceftazidime, cefotaxime, ceftriaxone, and aztreonam) in combi− nation with clavulanic acid. Moreover, the majority of the strains exhibited a high level of resistance to non−β−lac− tam antimicrobials (gentamicin, amikacin, co−trimoxazole). The MIC values of cefotaxime and cefrtiaxone were significantly higher than those of ceftazidime, suggesting that this resistance may result from CTM−X−type ESBLs. PCR based on primers specific for CTX−M−type β−lactamases confirmed the presence of the blaCTX−M gene in 31 (66%) donor strains and 23 (48.9%) transconjugants. Conclusions. The majority of the strains tested harbored conjugative plasmids coding for CTX−M−type ESBLs. Additionally, genes conferring resistance to antimicrobial agents other than β−lactams were often co−transferred to the recipient strain in the conjugation process, indicating that these determinants were carried by ESBL−encoding plasmids (Adv Clin Exp Med 2007, 16, 2, 239–247).