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, leqslant R: less-than-or-eq, slant55.4%) 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 Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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