Extended-spectrum beta-lactamase producing Enterobacteriaceae : aspects on detection, epidemiology and multi-drug resistance

• Beta-lactam antibiotics are the largest and most commonly used group of antimicrobial agents in Sweden as well as world-wide. They show very good tolerability and many of the drugs can be administrated orally. Bacteria expressing extended-spectrum beta-lactamases (ESBLs), enzymes hydrolysing penicillins and cephalosporins, may not respond to therapy using some of these antibiotics. The isolates are also often co-resistant to other antimicrobial agents, thus further limiting treatment options. Often parenterally administrated carbapenems is one of few safe treatment options left.In this thesis we have investigated the occurrence of ESBL producing Enterobacteriaceae in clinical isolates from Östergötland, Sweden, from 2002 until end of 2007 and the occurrence of multiresistance among ESBL producing E. coli. During these investigations we developed a simple method well suited for high-throughput analysis, for detection and sub typing of common ESBL genes.During the six year period, the prevalence of ESBL producing Enterobacteriaceae in Östergötland was very low, <1%, but increasing. The number of patients with ESBL producing E. coli increased significantly from 5 to 47 per year; K. pneumoniae remained between one and four per year. The genes found were dominated by CTX-M group 1 (67%), followed by group 9 (27%). There has been no reason to suspect an outbreak of nosocomial origin. The total consumption of antimicrobial agents was 10.7-12.1 DID per year in primary care; 1.14-1.30 DID per year in hospital care.Of eight oral agents tested, only three showed a generally high susceptibility; mecillinam (91%), nitrofurantoin (96%) and fosfomycin (99%). The corresponding figures for the fifteen tested parenterally administrated drugs were; amikacin (96%), tigecycline (99%), colistin (99%) and ≥99% susceptibility for the carbapenems.Sixty eight percent of the isolates were multiresistant. The most common multiresistance pattern was ESBL phenotype with decreased susceptibility to trimethoprim, trimethoprimsulfamethoxazole, ciprofloxacin, gentamicin and tobramycin. A significant difference in susceptibility between CTX-M groups, in favor of group 9 over group 1, was seen for many of the antibiotics tested; amoxicillin-clavulanic acid, aztreonam, cafepime, ceftibuten, ceftazidime, ciprofloxacin, gentamicin, piperacillin-tazobactam, temocillin, and tobramycin.In conclusion this thesis shows that the prevalence of ESBL producing Enterobacteriaceae in Östergötland was very low but increasing, and the total consumption of antimicrobial agents was stable. A majority of the isolates were multiresistant and a significant difference in susceptibility between CTX-M groups, in favor of group 9 over group 1, was seen for many of the antimicrobial agents tested.

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