[Characterization of the resistance mechanism to beta-lactams in Acinetobacter baumannii strains isolated in the university hospital Sahloul in Tunisia (2005)].
OBJECTIVE
The bacterial multiresistance to beta-lactams and imipenem is an emergent feature in the university hospital Sahloul in Tunisia. This study was conducted to elucidate natural and acquired mechanism of resistance to beta-lactams in strains of Acinetobacter baumannii isolated in different wards of the hospital.


METHODS
A specimen of 26 clinical strains of Acinetobacter baumannii was studied. beta-lactamases characterization was done by isoelectric focusing on gel of crude enzymatic extract, phenotypic tests for detection of extended spectrum beta-lactamases (ESBL) and metallo-beta-lactamases (MBL) and finally by amplification (PCR) and sequencing of genes encoding naturally occurring AmpC, the insertion sequence ISAbaI and oxacillinase with carbapenemase activity. Study of clonality of strains was performed by analysis of genomic DNA digested by the restriction enzyme ApaI and separated by pulsed field gel electrophoresis (PFGE).


RESULTS
The isoelectric focusing on gel revealed two bands of beta-lactamase activity with a pI upper than 8. None ESBL or MBL was detected. PCR for AmpC, ISAbaI and OXA-69 were positive for all studied strains. The sequencing of PCR products show high identity (99-100%) with genes described previously. PFGE analysis has demonstrated clonality of studied strains.


CONCLUSIONS
Resistance to beta-lactams including imipenem is associated to the hyper production of the AmpC enzyme and expression of OXA-69. Those enzymatic mechanisms are associated with the natural low permeability to beta-lactams which characterize Acinetobacter baumannii strains. High clonal relationship of studied strains proved by PFGE analysis has shown the necessity of implementation of strict hygienic rules and rational antibiotic usage.
Mansour
W
W
Unité des infections à bactéries multirésistantes aux antibiotiques, UR/29/04, laboratoire de microbiologie, CHU Sahloul, 4054 Sousse, Tunisie. wejmbr@yahoo.fr
Bouallegue
O
O
Dahmen
S
S
Boujaafar
N
N
D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000302:isolation & purification; D017931:DNA Primers; D024881:Drug Resistance, Bacterial; D018432:Drug Resistance, Multiple; D006785:Hospitals, University; D014416:Tunisia; D001618:beta-Lactamases / Q000378:metabolism; D047090:beta-Lactams / Q000494:pharmacology*
D017931:DNA Primers; D047090:beta-Lactams; D001618:beta-Lactamases