Negative correlation between biofilm formation and antibiotic sensitivity in clinical isolates of clonally related Acinetobacter baumannii

Abstract number: 1733_109

Fugazza G., Landini P., Migliavacca R., Spalla M., Nucleo E., Navarra A., Daturi R., Pagani L.

Objectives:Acinetobacter baumannii has emerged worldwide as an important nosocomial pathogen and an increasing number of outbreaks, mainly in ICUs, caused by multidrug resistant (MDR) strains, has been reported over the last years. Since biofilm formation by pathogenic bacteria might increase resistance to antimicrobial agents, we investigated the possibility that biofilm formation might be a resistance factor in A. baumannii.

Methods:A. baumannii analysed in this study included 35 clinical isolates, collected from 2 different hospitals in Northern Italy. Identification and susceptibility testing were carried out following standard procedures. Genotyping was performed by REP-PCR and PFGE analysis. Biofilm formation was tested in two different growth media: M9GSup, a defined growth medium with glucose as main carbon source, and LB, a rich, peptone-based medium. In addition, two different growth temperatures were tested: 37°C (host temperature) and 30°C (sub-optimal growth temperature).

Results: All isolates belonged to the same DNA group and showed either identical or highly similar profiles. Consistent with the identification results, all strains displayed the same MDR phenotype, but were sensitive to both tetracycline and imipenem. Four strains, chosen as representative, were tested for biofilm production and found capable of efficient biofilm formation, thus suggesting that production of adhesion factor is well conserved in this clone of A. baumannii. However, biofilm formation was greatly favoured when bacteria were grown in M9GSup; in contrast, little biofilm formation was observed in LB, possibly suggesting that adhesion factor production might be stimulated by growth on glucose. Growth at 30°C resulted in slight stimulation of biofilm formation compared to growth at 37°C in both media. Interestingly, MICs were roughly 4-fold lower in M9GSup medium for both tetracycline and imipenem, suggesting that sensitivity to antibiotics was actually increased in conditions favouring biofilm formation.

Conclusions: Our results suggest that biofilm formation by A. baumannii does not play a major role in antibiotic resistance. Increased sensitivity to imipenem in M9GSup medium is consistent with the reported bactericidal effect of this antibiotic on slow-growing bacterial cells. Future experiments will allow us to assess sensitivity of A. baumannii biofilm cells to imipenem, in order to evaluate its therapeutic potential against biofilm-related infections.

Session Details

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