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Mechanisms of environmental persistence of multidrug-resistant Acinetobacter baumannii isolates responsible for outbreaks in three Italian hospitals

Abstract number: P705

Landini P., Fugazza G., Spalla M., Migliavacca R., Giacobone E., Navarra A., Labonia M., Pagani L.

Objectives:Acinetobacter baumannii (Ab), an environmental Gram-negative bacterium, is considered one of the most dangerous emerging pathogens. The increasing number of outbreaks by clonally related multidrug resistant (MDR) Ab underlines the importance of clonal spread in nosocomial infections. We investigated the mechanisms of persistence in the hospital environment of Ab isolates responsible for outbreaks in three Italian hospitals.

Methods: 52 clinical isolates, collected from 2 acute care hospital and 1 long-term and rehabilitation facility between 2002–2006, were identified and tested for susceptibility with standard procedures. Genotyping was performed by PFGE analysis. Biofilm formation was determined by crystal violet assay. To assess contribution of cellulose production to biofilm formation, cultures were grown in the presence of different concentrations of cellulase.

Results: Genotyping by PFGE showed that most of MDR Ab isolates, susceptible to carbapenems, able to cause recurrent outbreaks in the studied settings belonged to the same DNA group (clone A), while the others, resistant to carbapenems too, belonged to clone B, which shows close relationship to European clone II. Both clone A and clone B isolates are proficient in biofilm formation, which was favoured by growth in nutrient-deficient medium in comparison to rich medium, and by lower growth temperature. Biofilm formation was inhibited by treatment with the lytic enzyme cellulase in both clones, suggesting that cellulose may act as an important adhesion factor in Ab. However, biofilms formed by clone A were less susceptible to cellulase treatment; in addition, clone A, but not clone B, displays a dark red phenotype on Congo Red-supplemented medium. These observations strongly suggest production of additional cell surface-associated structures involved in biofilm formation in clone A. Finally, clone A showed much stronger resistance to desiccation than clone B.

Conclusions: Our results show that biofilm formation in Ab is favoured in conditions more typical of the external environment rather than of the human host, confirming that biofilm might be involved in the Ab persistence in the environment. We show that cellulose is an important adhesion factor for Ab; however, the clone A identified in our study seems to possess additional biofilm determinants involved in resistance to environmental stresses such as desiccation, and thus potentially important in environmental persistence.

Session Details

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