High prevalence of plasmid-mediated 16S rRNA methylase gene rmtB among Escherichia coliclinical isolates from a Chinese teaching hospital

Abstract

BackgroundRecently, production of 16S rRNA methylases by Gram-negative bacilli has emerged as a novel mechanism for high-level resistance to aminoglycosides by these organisms in a variety of geographic locations. Therefore, the spread of high-level aminoglycoside resistance determinants has become a great concern.MethodsBetween January 2006 and July 2008, 680 distinct Escherichia coli clinical isolates were collected from a teaching hospital in Wenzhou, China. PCR and DNA sequencing were used to identify 16S rRNA methylase and extended-spectrum β-lactamase (ESBL) genes, including armA and rmtB, and in situ hybridization was performed to determine the location of 16S rRNA methylase genes. Conjugation experiments were subsequently performed to determine whether aminoglycoside resistance was transferable from the E. coli isolates via 16S rRNA methylase-bearing plasmids. Homology of the isolates harboring 16S rRNA methylase genes was determined using pulse-field gel electrophoresis (PFGE).ResultsAmong the 680 E. coli isolates, 357 (52.5%), 346 (50.9%) and 44 (6.5%) isolates were resistant to gentamicin, tobramycin and amikacin, respectively. Thirty-seven of 44 amikacin-resistant isolates harbored 16S rRNA methylase genes, with 36 of 37 harboring the rmtB gene and only one harboring armA. The positive rates of 16S rRNA methylase genes among all isolates and amikacin-resistant isolates were 5.4% (37/680) and 84.1% (37/44), respectively. Thirty-one isolates harboring 16S rRNA methylase genes also produced ESBLs. In addition, high-level aminoglycoside resistance could be transferred by conjugation from four rmtB-positive donors. The plasmids of incompatibility groups IncF, IncK and IncN were detected in 34, 3 and 3 isolates, respectively. Upstream regions of the armA gene contained ISCR1 and tnpU, the latter a putative transposase gene,. Another putative transposase gene, tnpD, was located within a region downstream of armA. Moreover, a transposon, Tn3, was located upstream of the rmtB. Nineteen clonal patterns were obtained by PFGE, with type H representing the prevailing pattern.ConclusionA high prevalence of plasmid-mediated rmtB gene was found among clinical E. coli isolates from a Chinese teaching hospital. Both horizontal gene transfer and clonal spread were responsible for the dissemination of the rmtB gene.

Characterization of an rmtB-carrying IncI1 ST136 plasmid in avian Escherichia coli isolates from chickens

“…This indicated that both horizontal gene transfer and clonal spread were responsible for the dissemination of the rmtB gene in the E. coli strains in this study. The prevalence of plasmids carrying rmtB has frequently been observed to be associated with the incompatibility group F (IncF) in humans and other animals in China (Yu et al, 2010;Hou et al, 2012), and with IncA/ C in humans and IncF in companion animals in Korea (Kang et al, 2008;So et al, 2012). However, all rmtB-carrying plasmids in the present study belonged to IncI1.…”

“…Recently, the rmtB gene has often been found to coexist with bla CTX-M and fosA3 (Hou et al, 2012;Lee et al, 2012;Sun et al, 2012;Pan et al, 2014), which could pose a threat to animal husbandry and public health. The dissemination of plasmids carrying rmtB has frequently been observed to be associated with the IncF and IncA/C incompatibility groups (Kang et al, 2008;Yu et al, 2010;Hou et al, 2012), whereas IncI1 plasmids harbouring rmtB are scarce. The aim of this study was to characterize the IncI1 plasmid carrying rmtB from avian Escherichia coli strains.…”

“…The positive rate for the rmtB gene was found to be much lower among Klebsiella pneumoniae and Proteus mirabilis in humans in Greece (Galani et al, 2012). In China, the rmtB gene is highly prevalent among Enterobacteriaceae strains from humans (Wu et al, 2009;Yu et al, 2010;Yang et al, 2011), and is also the most widespread among Enterobacteriaceae strains from pigs, chickens and companion animals (Chen et al, 2007;Du et al, 2009;Deng et al, 2011;Sun et al, 2012). The rmtB gene is located between the Tn2 transposon and insertion elements such as IS26, ISCR1 and ISCR3 (Doi et al, 2008;Du et al, 2009).…”

Study of Aminoglycoside Resistance Genes in Enterococcus and Salmonella Strains Isolated From Ilam and Milad Hospitals, Iran

“…The 16S rRNA methylase confers high-level resistance to 4, 6-substituted deoxystreptamines, including, arbekacin, amikacin, kanamycin, tobramycin and gentamicin, by posttranscriptional methylation of 16S rRNA leading to loss of affinity for aminoglycosides (8). Despite the existence of more than 85 aminoglycoside-modifying enzymes, only a limited number of them, ANT(2′′)-I, AAC(6′)-I, AAC(3)-I, AAC(3)-II, AAC(3)-III, AAC(3)-IV and AAC(3)-VI, appear to have been undergoing selection process and causing the majority of aminoglycoside resistance (9).…”

Identification of aac(2')-I Type b aminoglycoside-modifying enzyme genes in resistant Acinetobacter baumannii

“…These enzymes can modify specific aminoglycoside groups that enter bacterial cells; this modification results in a loss of aminoglycoside biological activities (Mingeot-Leclercq et al, 1999). In addition, the mechanism is related to the 16S rRNA methylase (Mingeot-Leclercq et al, 1999;Yu et al, 2010) and drug "efflux pumps" (Sun et al, 2010;Luo et al, 2011), which have been widely examined in recent years.…”