Study On The Distribution Of 16S RRNA Methylase Encoding Genes In Acinetobacter Baumannii

Acinetobacter spp. is glucose-nonfermenting and gram-negative bacillus which can survive widely in the water, soil, different hospital environments, and skin. Nosocomial infections caused by Acinetobacter species include pneumonia, meningitis, bloodstream, urinary tract, surgical wound, and soft tissue infections. Following the widely use of broad-spectrum antimicrobials, multi-resistant A. baumannii increased quickly. Acinetobacter baumannii has emerged as an important nosocomial pathogen in the world. It caused nosocomial outbreak in many countries. It is difficult to deal with in clinic.Aminoglycosides are used to treat a broad range of lifethreatening infections in humans and animals. The most important mechanism of aminoglycoside resistance is the enzymatic modifications of the drugs. Another important enzymatic modification is the posttranscriptional rRNA methylation by 16S rRNA methylases. This modification confers a high-level resistance to 4, 6-substituted deoxystreptamines, including amikacin, due to a loss of affinity of 16S rRNA to aminoglycosides.We collected 700 clinical isolates of Acinetobacter baimannii from Dec 2004 to Dec 2005 among 25 hospitals in China. Agar dilution method was used to determinate the MIC of these strains to 5 aminoglycosides. Three 16S rRNA methylase genes, armA, rmtA and rmtB, were detected by PCR-based assays. PCR products were purified, cloned and sequenced. The homology of armA-positive strains were analyzed by pulse-field gel electrophoresis (PFGE). Plasmid was extracted, conjugation and southern blot were performed.The resistance rates to tobramycin, amikacin, gentamicin, isepamicin, netilmicin were 67.7%, 70.9%, 75.7%, 63.5%, and 71.5%, respectively. 334 armA-positive isolates were identified. No rmtA, rmtB gene was detected. PFGE analysis indicated that 334 armA-positive isolates were mainly classified into 3 clones. Clone A, B and C had widely spread in all of these provinces. No plasmid was extracted and conjugation was not successful, despite multiple attempts. Southern blot confirmed that the armA gene was located on the chromosome Apal digested DNA patterns of these strains.Nosocomial spread of armA-producing Acinetobacter baumannii is quite severe in China. ArmA gene was located on the chromosome of these strains.