Identification of plasmid- and integron-borne bla IMP-1 and bla IMP-10 in clinical isolates of Serratia marcescens

Abstract

The emergence of carbapenem-hydrolysing metallo-b-lactamases (MBLs) is a serious threat to the clinical utility of carbapenems. This study identified plasmid-and integron-borne bla IMP-1 and bla in clinical isolates of Serratia marcescens. The bla IMP-1 and bla IMP-10 gene cassettes were carried by a class 1 integron and followed by the aac(69)-IIc gene cassette. The bla IMP-1 and bla IMP-10 gene cassettes were preceded by a weak P ant promoter, TGGACA(N) 17 TAAGCT, and an inactive P2 promoter, TTGTTA(N) 14 TACAGT. These genes were easily transferred to Escherichia coli by conjugation and transformation, indicating that they are located on transferable plasmids. Due to the acquisition of bla IMP-1 , the susceptibility of E. coli transconjugants to imipenem, meropenem, panipenem and biapenem decreased by 32-, 256-, 64-and 128-fold, respectively. In comparison, after gaining bla IMP-10 , the susceptibility of E. coli transconjugants to the four carbapenems decreased by 64-, 2048-, 256-and 64-fold, respectively. Strains harbouring bla IMP-10 showed higher-level resistance to imipenem, meropenem and panipenem than the strains harbouring bla IMP-1 , although the nucleotide sequences of the class 1 integrons carrying bla IMP-10 and bla IMP-1 were identical except for a single point mutation. INTRODUCTIONCarbapenems are relatively stable agents that act against extended-spectrum b-lactamases produced by Gram-negative rods, and are one of the first-choice antibiotics for the treatment of Serratia marcescens infections (Gilbert et al., 2005). However, the occurrence and spread of genes encoding metallo-b-lactamases (MBLs) including IMP, VIM, SPM and GIM have been reported in a variety of clinical isolates of Enterobacteriaceae from 28 countries (Walsh et al., 2005). The clinical significance of MBLs is further highlighted by their ability to hydrolyse almost all b-lactams except for monobactams, and by the fact that to date there is no clinically available inhibitor (Bush, 1998;Livermore & Woodford, 2000;Nordmann & Poirel, 2002).The bla IMP-1 gene, which encodes IMP-1 MBL, was the first MBL determinant reported, initially in a clinical isolate of S. marcescens from Japan in 1994 (Ito et al., 1995; Osano et al., 1994). To date, the nucleotide sequences of 24 IMP variants have been determined (Lahey Clinic, 2008). bla IMP-10 is a point mutation derivative of bla IMP-1 and has been identified in clinical isolates of Pseudomonas aeruginosa and Alcaligenes xylosoxidans (Iyobe et al., 2002;Zhao et al., 2008). To our knowledge, the bla IMP-10 gene has not been identified among Enterobacteriaceae strains.MBL genes are usually found as gene cassettes in integrons, mostly in class 1 integrons (Shibata et al., 2003). An integron is a mobile DNA element that can capture and carry genes, particularly antibiotic-resistance genes, by site-specific recombination (Bennett, 1999;Stokes & Hall, 1989). Five classes of integron are known to play a role in the dissemination of antibiotic resistance, and class 1 integrons are the most ext...

Identification of a New Integron Harboring bla IMP-10 in Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates

“…Initially reported in 1997 (18), bla IMP-10 has been harbored by distinct integrons in Gram-negative bacilli, especially in Japan (18,19). Hu and Zhao reported Serratia marcescens isolates carrying bla IMP-1 or bla IMP-10 genes in class 1 integrons with identical cassette arrangements (19), which is similar to our findings.…”

Relevance of resistance levels to carbapenems and integron-borne bla IMP-1, bla IMP-7, bla IMP-10 and bla VIM-2 in clinical isolates of Pseudomonas aeruginosa

“…Using E. coli transconjugants and transformants, it was also observed that the bla IMP-10 -positive strains showed much higher levels of resistance to IPM, MEPM and PAPM than the strains harbouring bla IMP-1 (Hu & Zhao, 2009). The E. coli transconjugants and transformants are more suitable models than wild-type strains of S. marcescens and P. aeruginosa because factors such as the outer-membrane barrier, the efflux system and the chromosomal AmpC blactamases that are possibly possessed by these wild-type strains can be excluded.…”

Class 1 integrons in non-clonal multidrug-resistant Acinetobacter baumannii from Iran, description of the new bla IMP-55 allele in In1243

“…One of the major cassette-borne resistance genes reported in class 1 integron in recent years is the bla IMP gene encoding metallo-b-lactamase IMP belonging to molecular class B of b-lactamase (Hu et al, 2009). The IMP variants confer a high level of carbapenem resistance in A. baumannii isolates, as well as the very broad substrate specificity of IMP enzymes, including oxyiminocephalosporins, carbapenems and serine b-lactamase inhibitors, which accounts for their important clinical relevance (Poirel et al, 2006;Laraki et al, 1999).…”