Prevalence of 16S rRNA methylase, modifying enzyme, and extended-spectrum beta-lactamase genes amongAcinetobacter baumanniiisolates

Abstract

Multidrug-resistant Acinetobacter baumannii has become a worldwide problem, and methylation of 16S rRNA has recently emerged as a new mechanism of resistance to aminoglycosides, which is mediated by a newly recognized group of 16S rRNA methylases. 16S rRNA methylase confers a high-level resistance to all 4,6-substituted deoxystreptamine aminoglycosides that are currently used in clinical practice. Some of the A. baumannii isolates have been found to coproduce extended-spectrum beta-lactamases (ESBLs), contributing to their multidrug resistance. The aim of this study was to detect the determinants of the 16S rRNA methylase genes armA, rmtA, rmtB, rmtC, rmtD, rmtE, and npmA, the modifying enzyme genes aac(6')-Ib, ant(3″)-Ia, aph(3')-I, and the extended-spectrum beta-lactamase genes bla(TEM), bla(SHV), and bla(CTX-M-3) among A. baumannii isolates in northeastern Sichuan, China. Minimum inhibitory concentrations (MICs) of 21 different antimicrobial agents against the A. baumannii isolates were determined. The clinical isolates showed a high level of resistance (MIC≧256 μg/ml) to aminoglycosides, which ranged from 50·1 to 83·8%. The resistances to meropenem and imipenem, two of the beta-lactam antibiotics and the most active antibiotics against A. baumannii, were 9·1 and 8·2%, respectively. Among 60 amikacin-resistant isolates, only the 16S rRNA methylase gene armA was found to be prevalent (66·7%), but the other 16S rRNA methylase genes rmtA, rmtB, rmtC, rmtD, rmtE, and npmA were not detected. The prevalences of the modifying enzyme genes aac (6')-Ib, ant (3″)-Ia, and aph (3')-I were 51·7, 81·7, and 58·3%, respectively, which are different from a previous study in which the occurrences of these genes were 3, 64, and 72%, respectively. Among the 40 isolates that were armA-positive, the prevalences of bla(TEM), bla(SHV), and bla(CTX-M-3) genes were detected for the first time in China, and their occurrences were 45, 65, and 52·5%, respectively. In all, A. baumannii with all the 16S rRNA methylase, modifying enzyme, and ESBL genes is extremely prevalent in northeastern Sichuan, China, posing a serious clinical concern with a major therapeutic threat in the future.

Prevalence of carbapenemases among high-level aminoglycoside-resistant Acinetobacter baumannii isolates in a university hospital in China

“…In addition, further cases were reported in Korea (20,23), India (24), France (25), Bulgaria (26), Italy (27), Latvia (28), East Africa (29), Yemen (30), Japan (31), Brunei (32), Egypt (33) and China (21,34,35). The authors of the present study previously determined that extended-spectrum β-lactamase and 16S rRNA methylase are coproduced in A. baumannii (36). However, the high-level resistance to aminoglycosides, coupled with carbapenem resistance in A. baumannii , were not reported over the 4-year period in China, particularly in western China.…”

“…Primers listed in Table I were synthesized by Sangon Biotech Co., Ltd.. The PCR thermal cycling conditions were as follows: Initial denaturation at 94°C for 5 min in order to obtain partial activation of Taq polymerase; then, the number of cycles was increased to 30, each consisting of a denaturation step for 30 sec (at 94°C), an annealing step for 30 sec (at 55°C for armA , rmtA , rmtB , rmtC , rmtD , rmtE , rmtF , rmtG , rmtH and npmA , at 53°C for ant(2″)-Ia , aph(3′)-1a , aac(3)-Ia and aac(3)-IIa , and at 56°C for aac(6′)-Ib ) and an extension step for 30 sec (at 72°C). Each amplification experiment included a blank containing the reagent except for target DNA.…”

“…Acinetobacter baumannii is an important opportunistic pathogen that causes various types of human infections and has become a primary cause of nosocomial infections because of its broad antimicrobial resistance (1–3). Aminoglycosides, a type of broad-spectrum antibiotics, continue to serve an important role in treating serious infections caused by gram-negative bacteria (4).…”

“…The results showed that 75 (63.56%) isolates were high-level resistant to aminoglycosides, including gentamicin and amikacin (minimum inhibitory concentration, ≥256 µg/ml). Aminoglycoside-resistant genes ant(2″)-Ia , aac(6′)-Ib , aph(3′)-Ia , aac(3)-Ia , aac(3)-IIa , armA , rmtA , rmtB , rmtC , rmtD , rmtE , rmtF , rmtG , rmtH and npmA , and carbapenem-resistant genes bla OXA-23 , bla OXA-24 , bla OXA-51 , bla OXA-58 , bla SIM , bla IMP , bla NDM-1 and bla KPC , were analyzed using polymerase chain reaction. The positive rate of ant(2″)-Ia , aac(6′)-Ib , aph(3′)-Ia , aac(3)-Ia and aac(3)-IIa was 66.95, 69.49, 42.37, 39.83 and 14.41%, respectively.…”

The Genetic Analysis of an Acinetobacter johnsonii Clinical Strain Evidenced the Presence of Horizontal Genetic Transfer

“…There are multiple descriptions of phage related genes, cryptic prophages and prophage structures in Acinetobacter sp. [54, 71, 72, 74]. However, the role of phages in Acinetobacter is poorly understood.…”