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Antimicrobial susceptibility to parenteral and oral agents in a largely polyclonal collection of CTX‐M‐14 and CTX‐M‐15‐producing

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Titelman E, Iversen A, Kahlmeter G, Giske CG. Antimicrobial susceptibility to parenteral and oral agents in a largely polyclonal collection of CTX‐M‐14 and CTX‐M‐15‐producing Escherichia coli and Klebsiella pneumoniae. APMIS 2011; 119: 853–63.

Activity of oral and parenteral antimicrobials against consecutively isolated extended‐spectrum β‐lactamase (ESBL)‐producing Escherichia coli (n = 149) and Klebsiella pneumoniae (n = 20) was determined, and susceptibility test methods were compared for parenteral β‐lactams. Polymerase chain reaction (PCR) targeting bla CTX‐M, bla SHV and bla TEM, and DNA sequencing and epidemiological typing with pulsed‐field gel electrophoresis were performed. PCR targeting pabB was screened for E. coli O25b‐ST131. Minimum inhibitory concentrations (MICs) were determined using Etest and broth microdilution. Disc diffusion was performed according to European Committee on Antimicrobial Susceptibility Testing (EUCAST). Dominating genotypes were bla CTX‐M‐15 (75%) and bla CTX‐M‐14 (23%). Four E. coli clusters (7–18 isolates) were found. Forty‐two per cent of E. coli belonged to O25b‐ST131. Ciprofloxacin resistance was 72%, trimethoprim resistance was 70%. Among E. coli, resistance to mecillinam (13%), nitrofurantoin (7%) and fosfomycin (3%) was low, although resistance was high in K. pneumoniae (25%, 60%, 85%). Susceptibility to ertapenem was 99%, piperacillin‐tazobactam 91%, tigecycline 96% and temocillin 76%. Susceptibility rates obtained with broth microdilution and Etest were in agreement for cefotaxime (2 vs 1%) and ceftazidime (9 vs 11%), but not for piperacillin‐tazobactam (59 vs 91%). With disc diffusion major errors occurred with piperacillin‐tazobactam (18/169). Several therapeutic alternatives exist for ESBL‐producing E. coli, but few exist for K. pneumoniae. Disc diffusion and Etest can accurately predict susceptibility to cefotaxime and ceftazidime, but not to piperacillin‐tazobactam with the present breakpoints.
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Document Type: Research Article

Affiliations: Clinical Microbiology, Karolinska Institutet-MTC, Karolinska University Hospital, Solna, Stockholm;

Publication date: December 1, 2011

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