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In vitro activity of tigecycline and comparators against Acinetobacter baumannii isolated from severe infections in Italy

Abstract number: 1734_17

Mezzatesta M., Trovato M., Nicolosi V., Nicolosi D., Nicoletti G., Cassone A., Fadda G., Schito G., Stefani S.

Objectives: In a recent multi-centre survey (2003–2004), conducted in 45 laboratories throughout Italy with the aim of monitoring microrganisms responsible for severe infections and their antibiotic resistance, Acinetobacter baumannii was isolated from the ICU of 12 centres as the third most frequent pathogen. Due to the increasing importance of this microrganism in hospital epidemiology, which is partly due to its success in acquiring resistance to carbapenem or showing a multi-drug-resistance (MDR) phenotype, it is mandatory to look at the activity of new antimicrobial agents.

Methods: Included in the study were 88 clinically significant strains of A. baumannii. Tigecycline and comparators were tested by MICs following the CLSI guidelines. For the carbapenem resistant strains, a preliminary phenotypic screening for the presence of metallo-enzymes (MBL) was performed by Etest, and PCR was used to investigate the presence of blaOXA, blaIMP and blaVIM genes. PFGE was performed to test clonality.

Results:A. baumannii was a frequent cause of ventilator-associated pneumonia and bacteraemia. Resistance to ceftazidime, ciprofloxacin and aztreonam was widespread in almost 90% of strains; resistance to imipenem was 51% and resistance to meropenem was 64%, amikacin and gentamicin were active against 30% of strains and colistin was very active.

Tigecycline had a MIC90 value of 2 mg/L and our strains showed a unimodal distribution of susceptibility, demonstrating that this new drug is more active than other tetracyclines. Among the 45 imipenem-resistant isolates (MIC gt; 16 mg/L) only 17 strains showed a reduction in the imipenem MIC with EDTA indicating MBL activity, but no PCR products for blaIMP and blaVIM were obtained from the strains analysed. Further studies are in progress for the characterisation of the blaOXA resistance determinants. PFGE analyses showed the existence of a multiresistant A. baumannii clone, widespread in different hospitals.

Conclusion: In conclusion, tigecycline showed a potent activity against the MDR A. baumannii strains maintaining the same MIC90 of 2 mg/L against the majority of carbapenem-resistant strains. The use of additional molecular techniques to fingerprint isolates will provide further information on these clinically important MDR A. baumannii.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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