[Study of plasmid-mediated 16S rRNA methylase genes and drug-resistant transferability of Acinetobacter baumannii isolated from burn ward].

OBJECTIVE: To investigate the drug-resistance of Acinetobacter baumannii (Ab) isolated from patients in burn ward, and study the incidence of 16S rRNA methylase genes mediated high-level aminoglycoside drug-resistance and its mechanism of transfer.

METHODS: A total of 40 Ab clinical isolates were collected from burn ward in Gansu Province People's Hospital from May 2006 to Dec. 2007. The sensitivity of Ab for 20 antibiotics were determinated by K-B agar diffusion. The minimal inhibitory concentrations (MIC) of amikacin, gentamicin, tobramycin, netilmicin, isepamicin and kanamycin against Ab strains were determinated by agar dilution. Five kinds of 16S rRNA methylase genes including armA, rmtA, rmtB, rmtC, rmtD were amplified by PCR, the positive PCR-products were purified and sequenced, and the plasmid were extracted by alkaline lysis. The transferability of drug-resistance were determinated by conjugation and plasmid transformation tests.

RESULTS: The drug-resistance rates of Ab against six aminoglycosides antibiotics was 72.5%, 72.5%, 70.0%, 67.5%, 70.0%, 70.0%, respectively. Twenty five strains were resistant to six aminoglycosides antibiotics (62.5%), among which 10 isolates were armA-positive (40.0%); rmtA, rmtB, rmtC and rmtD-positive isolates were not found. Ten transformants and 10 conjugates showed high-level resistance against aminoglycosides antibiotics, all of which the value of MIC > or = 256 microg/mL carried armA gene.

CONCLUSIONS: The drug-resistance of Ab clinical isolates have high drug-resistance. 16S rRNA methylases gene exists in Ab and locates in plasmid chromosome.