Study on resistant mechanism of two clinical strains of Enterobacter aerogenes to ertapenem

Abstract:

ObjectiveTo study resistant mechanisms of two clinical strains of Enterobacter aerogenes (Ea293 and Ea2880)to ertapenem. MethodsThe minimum inhibitory concentrations (MICs) of antimicrobial agents were determined by microbroth dilution method, drug resistance of strains to imipenem，meropenem，and ertapenem were determined by KB test; carbapenemase was confirmed by modified Hodge test, carbapenemase genes（KPC，IMP1 group，IMP2 group，VIM）, broadspectrum and extendedspectrum βlactamases genes（TEM，SHV，CTXM1 group，CTXM2 group，CTXM9 group） were amplified by polymerase chain reaction (PCR), and sequences were analysed; Outer membrane protein (Omp) was analyzed by sodium dodecylsulfatepolyacrylamide gel electrophoresis (SDSPAGE) and the coding gene OmpE36 was amplified by PCR. ResultsAntimicrobial susceptibility test showed that Ea293 and Ea2880 were all resistant to ertapenem. Among amplified 4 carbapenemase genes and 5 broadspectrum and extendedspectrum genes, only  blaSHV and blaCTXM9 group ESBLs in Ea2880 were positive, BlaSHV DNA sequence was SHV11 type. SDSPAGE showed that compared with ertapenemsensitive isolate Ea1885, ertapenemresistant isolate Ea293 and Ea2880 lacked the protein band with 42kD which might be the outer membrane protein gene OmpE36. OmpE36 was amplified by PCR, Ea2880 appeared the excepted bands, but Ea293 didn’t. The similarity of DNA and amino acid sequences of OmpE36 of Ea2880 with the standard Enterobacter aerogenes ATCC13048 from GenBank were both 87%.ConclusionThe resistance of clinical strains of Enterobacter aerogenes Ea293 and Ea2880 to ertapenem might be associated with the loss of outer membrane protein gene OmpE36. Furthermore，Ea2880 might be associated with production of CTXM9 group ESBLs.