Profiling of 16S rRNA methylase genes and the flanking sequences in extensively drug resistant Pseudomonas aeruginosa / 中国感染与化疗杂志

Objective To profile 16S rRNA methylase genes and the flanking sequences in extensively drug resistant (XDR) Pseudomonas aeruginosa. Methods A total of 59 strains of XDR P. aeruginosa were collected. MICs of antimicrobial agents against these strains were determined by agar dilution method. The genes encoding 16S rRNA methylase (armA, rmtA, rmtB, rmtC, rmtD, rmtE, and npmA) were analyzed by PCR. The homology of strains was studied by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR). The structure of armA and rmtB flanking regions were characterized. Results The overall prevalence of armA or rmtB genes was 62.7％ (37/59) in XDR P. aeruginosa isolates, specifically armA positive in 17 strains and rmtB positive in 22 strains. The rmtA, rmtC, rmtD, or npmA gene was not identified in any strain. ERICPCR generated 19 types (or clones) from the 59 strains. The 17 armA-positive strains were distributed in 3 clones, and 88.2％ of the armA-positive strains (15) belonged to clone D. The rmtB gene was dispersed in 9 clones. Flanking sequence analysis demonstrated that armA gene was located in a mobile element carrying multiple transposases. The sequence of the mobile element showed 99％ similarity with the sequence of armA-positive plasmid carried by E. coli and A. baumannii. The rmtB gene was also located in a mobile element containing multiple transposases. The sequence of the mobile element was highly consistent with that of rmtB-positive plasmid carried by E. coli and K. pneumoniae. Conclusions The genes encoding 16S rRNA methylase are prevalent in XDR P. aeruginosa strains. All the genes were identified in high-level gentamicin-resistant strains. Clonal dissemination may explain the spread of armA among P. aeruginosa isolates.

In Vivo Selection of Pan-Drug Resistant Acinetobacter baumannii during Antibiotic Treatment

PURPOSE: Colistin resistance in Acinetobacter baumannii (A. baumannii) is mediated by a complete loss of lipopolysaccharide production via mutations in lpxA, lpxC, and lpxD gene or lipid A modifications via mutations in the pmrA and pmrB genes. However, the exact mechanism of therapy-induced colistin resistance in A. baumannii is not well understood. MATERIALS AND METHODS: We investigated the genotypic and phenotypic changes that underlie pan-drug resistance mechanisms by determining differences between the alterations in extensively drug-resistant (XDR) A. baumannii (AB001 and AB002) isolates and a pan-drug resistant (PDR) counterpart (AB003) recovered from one patient before and after antibiotic treatment, respectively. RESULTS: All three clinical isolates shared an identical sequence type (ST138), belonging to the global epidemic clone, clonal complex 92, and all produced OXA-23 carbapenemase. The PDR AB003 showed two genetic differences, acquisition of armA gene and an amino acid substitution (Glu229Asp) in pmrB gene, relative to XDR isolates. No mutations were detected in the pmrA, pmrC, lpxA, lpxC, or lpxD genes in all three isolates. In matrix-assisted laser desorption ionization-time of flight analysis, the three isolates commonly showed two major peaks at 1728 m/z and 1912 m/z, but peaks at 2034 m/z, 2157 m/z, 2261 m/z, and 2384 m/z were detected only in the PDR A. baumannii AB003 isolate. CONCLUSION: Our results show that changes in lipid A structure via a mutation in the pmrB gene and acquisition of armA gene might confer resistance to colistin and aminoglycosides to XDR A. baumannii strains, resulting in appearance of a PDR A. baumannii strain of ST138.

The prevalence of 16S rRNA methylase gene armA and drug resistance in Acinetobacter baumannii / 中华微生物学和免疫学杂志

Objective To investigate the prevalence of 16S rRNA methylase gene armA and to analyze their effect on the drug resistance in multi drug-resistant strains of Acinetobacter baumannii . Methods A total of 72 Acinetobacter baumannii isolates were collected from the Second Xiangya Hospital from Jan. 2008 to Dec. 2008. The size of inhibitory zone of these strains to gentamycin, tobramycin and amikacin were determinate using Kirby-Bauer( K-B) method. The 16S rRNA methylase genes armA were detected by PCR. PCR products were purified and sequenced. Then we used randomly amplified polymorphic DNA method (RAPD) genotyping technology for the establishment of DNA fingerprinting. In addition, we compared drug sensitivity test with RAPD technology. Results Twenty isolates of 72 strains were armA positive and the resistance rates of the strains with armA gene to gentamycin, tobramycin, amikacin were 90.0% , 90.0% and 90. 0% , respectivily. armA positive stains were divided into 7 types using RAPD technology. A genotype was the advantage type. Conclusion The study showed that 16S rRNA methylases gene armA was prevalent in Acinetobacter baumannii which could lead to resistant to almost all aminoglycosides at a high level. And the main form of armA gene prevalence in our hospital was the spread of the same clone strain inside and outside of clinic department.