Bactericidal activity of ertapenem against A. baumannii
Abstract number: 1733_1573
Schneiders T., Amyes S.
Ertapenem is a new carbapenem targetted for clinical use against fermenters such as E. coli and Klebsiella spp. but with reduced or weak activity against non-fermenting Gram-negative bacteria such as Acinetobacter baumannii and Pseudomonas aeruginosa. Both Acinetobacter spp. and Pseudomonas spp. are established pathogens in the hospital setting and are resistant to a range of antibiotics which include the carbapenems. Since the carbapenems (e.g. meropenem) represent the last line of antibiotics against both Acinetobacter and Pseudomonas spp., it is imperative that this antibiotic class is preserved. Due to its reduced activity the introduction and use of ertapenem, suggests a potential for resistance development in these bacteria. The combination of increasingly carbapenem-resistant bacteria and a less efficacious antibiotic such as ertapenem against a rapidly evolving bacterial population could result in the emergence of completely untreatable bacteria. The efficacy of ertapenem against three characterised strains of A. baumannii was determined using time-kill studies at 4 times the MIC. The three strains of A. baumannii were ATCC 19606, a carbapenem sensitive clinical A. baumannii isolate, SD16, and another carbapenem sensitive A. baumannii clinical isolate, E13, which harbours a mutS mutation. As a comparator antibiotic, meropenem, was used. Against ATCC 19606 and at 4 times the MIC, ertapenem reduced the viable count by 2 log10 reduction in 3 hours and extended the killing to greater than 4 log10 after 24 hours. Against the sensitive clinical isolate SD16, ertapenem exerted a 3 log10 reduction in 3 hours and after 24 hours reduced the viable count to a 4 log10 reduction. Of note, the levels of reduction in viable cell counts by ertapenem were comparable to meropenem. Interestingly against the mutS mutant, E13, the viable counts obtained with either meropenem or ertapenem, showed little or no reduction over the 3 hour period which was in contrast to that observed with ATCC19606 and SD16. However a reduction to 4 log10 was observed with both ertapenem and meropenem after 24hrs. The results obtained here clearly demonstrate that ertapenem inhibits non-fermenters such as A. baumannii with similar efficacy as meropenem. These findings are significant as it is the first to describe the effect ertapenem has on A. baumannii and serves to re-examine the role of ertapenem either as a potential therapeutic option or a selector of resistance.
|Session name:||European Society of Clinical Microbiology and Infectious Diseases|
|Location:||ICC, Munich, Germany|
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