Increased antimicrobial susceptibility profiles among polymyxin-B-resistant Acinetobacter baumannii clinical isolates
Abstract number: P1159
Mendes R., Fritsche T., Sader H., Jones R.
Objective: Infections caused by multidrug-resistant (MDR) A. baumannii have become a major treatment challenge, requiring the re-introduction of polymyxins into clinical practice. Given this situation, the emergence of polymyxin B (PB) resistance (R) is expected. Recently, increased antimicrobial susceptibility (S) among in vitro passaging of colistin-R A. baumannii isolates was observed when compared with the parent colistin-S strains. The aim of this study was to compare the S profile between PB-R and PB-S A. baumannii patient isolates submitted to the SENTRY Antimicrobial Surveillance Program.
Methods: A collection of 5,561 A. baumannii clinical isolates was S tested by the CLSI broth microdilution method and the S rates of 24 epidemiologically unrelated PB-R isolates were compared to those of PB-S isolates. S rates were analysed by chi2 test using the Epi Info Version 3.4.1 software package. P values <0.05 were considered to be statistically significant.
Results: The majority of the antimicrobials tested showed limited spectrums of activity (S rates, 55.4%) against the PB-S A. baumannii group, except for imipenem (73.2%), meropenem (76.5%) and some tetracyclines. Doxycycline, minocycline and tigecycline showed the highest S rates 74.7, 91.7 and 97.0%, respectively. Overall, the polymyxin-R group showed a higher S rate for the vast majority of antimicrobials tested. This shift was not observed among those antimicrobial agents with higher activity against the PB-S group (i.e. carbapenems and tetracyclines). Statistically significant differences were observed among most drugs showing lower activity, including ampicillin/sulbactam (S rate 3× higher), aztreonam (4×), cefoxitin (20×), ceftriaxone (2×) and cefuroxime (8×). Tigecycline was highly active regardless the susceptibility to PB.
Conclusions: PB-R A. baumannii clinical isolates showed higher S rates when compared to PB-S isolates for the majority of antimicrobials tested. These findings suggest that possible lipopolysaccharide modifications among PB-R bacterial cells may increase permeability to the antimicrobial agents. These data may provide additional insights for combination therapeutic options and also for possible novel antimicrobial agents in drug development.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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