Abstract
Imipenemase-6 (IMP-6) type carbapenemase-producing Enterobacteriaceae is regarded as dangerous due to its unique lack of antimicrobial susceptibility. It is resistant to meropenem (MEPM) but susceptible to imipenem (IPM). In addition to carbapenemase, outer membrane porins and efflux pumps also play roles in carbapenem resistance by reducing the antimicrobial concentration inside cells. Extended-spectrum β-lactamase (ESBL) is transmitted with IMP-6 by the plasmid and broadens the spectrum of antimicrobial resistance. We collected 42 strains of IMP-6-producing Escherichia coli and conducted a molecular analysis of carbapenemase, ESBL, porin, efflux, and epidemiological characteristics using plasmid replicon typing. Among the 42 isolates, 21 strains were susceptible to IPM (50.0%) and 1 (2.4%) to MEPM. Seventeen strains (40.5%) co-produced CTX-M-2 type ESBL. We found that the relative expression of ompC and ompF significantly correlated with the MIC of IPM (p = 0.01 and p = 0.03, respectively). Sixty-eight% of CTX-M-2-non-producing strains had IncI1, which was significantly different from CTX-M-2-producing strains (p < 0.001). In conclusion, 50.0% of our IMP-6-producing strains were non-susceptible to IPM, which is different from the typical pattern and can be attributed to decreased porin expression. Further studies investigating other types of carbapenemase are warranted.
Highlights
The prevalence of imipenemase-6 (IMP-6) type carbapenemase-producingEnterobacteriaceae (CPE) is increasing in Japan, and this is regarded as dangerous due to its unique lack of antimicrobial susceptibility [1,2]
CPE can produce a variety of carbapenemases, which are divided into three groups as class A, class B, and class D according to the Ambler classification [4]
Previous study from Osaka showed that 130 (97.0%) of 134 carbapenem-resistant E. coli produced IMP-6 [1]. Their susceptibility rates to MEPM and IPM were 0% and 100.0%, respectively, which is a typical pattern of IMP-6-producing carbapenem resistance Enterobacteriaceae (CRE)
Summary
Enterobacteriaceae (CPE) is increasing in Japan, and this is regarded as dangerous due to its unique lack of antimicrobial susceptibility [1,2]. They are generally resistant to meropenem (MEPM), they are susceptible to imipenem (IPM) [2,3]. In Japan, the most common carbapenemase type is IMP, one of the class B carbapenemases It exhibits metallo-β-lactamase and is able to decompose almost all βlactam drugs, including carbapenems, by a wide range of instrumental specificity. CPE often co-produces extended-spectrum β-lactamase (ESBL), which inactivates penicillins, cephalosporins, and monobactams [3,6] for wider spectrum antimicrobial resistance. IMP-6 generally does not inactivate penicillins and monobactams [2,7], but if an IMP-6-producing strain co-produces
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