Abstract
To determine evolution and genotype of new chromosomal AmpC $\beta$-lactamases among clinical isolates of Enterobacter species, we performed antibiotic susceptibility testing, pI determination, sequencing, and phy-logenetic analysis using developed expression/secretion vector. Six isolates have shown to produce AmpC $\beta$-lactamases. Six genes of AmpC $\beta$-lactamases that are responsible for the resistance to cephamycins (cefoxitin and cefotetan), amoxicillin, cephalothin, and amoxicillin-clavulanic acid were cloned and characterized in pMSG12119. Insert fragment containing the ampC genes was sequenced and found to have an open reading frame coding for 381-amino-acid $\beta$-lactamase. The nucleotide sequence of four ampC genes ($bla_EcloK992004.l$, $bla_EcloK995120.1$, $bla_EcloK99230$, and $bla_EareK9911729$) shared considerable homology with that of chromosomal ampC gene ($bla_EcloMHN1$) of E. cloacae MHN1 (more than 99.6% identity). The sequences of two ampC genes ($bla_EcloK9973$ and $bla_EcloK9914325$) showed close similarity to the chromosomal ampC gene ($bla_EcloQ908R$) of E. clo-acae 908R (99.7% identity). The results from phylogenetic analysis suggested that six ampC genes could be originated from $bla_EcloMHN1$ / or $bla_EcloQ908R$ / MIC patterns and exact pI values of six transformants indicated that the developed expression/secretion vector (pMSG1219) was suitable for the characterization of foreign genes in E. coli strain.
임상균주인 Enterobacter spp.가 생성하는 신규 chromosomal AmpC $\beta$-lactamases의 유전자형 및 진화적 측면을 고찰하기 위해서 항생제 감수성 시험, pI값 측정, DNA 염기서열 분석, 진화적 유연관계를 새로운 발현$.$분비 벡터를 이용하여 수행하였다. 6개 임상균주에서 cephamycins (cefoxitin and cefotetan), amoxicillin, cephalothin 및 amoxicillin-clavulanic acid에 내성 요인인 AmpC $\beta$-lactamase 유전자를 pMSG1219에 cloning하여 그 특성을 조사하였다. 381-amino-acid $\beta$-lactamase를 암호화 하는 4개의 ampC 유전자($bla_EcloK992004.1$, $bla_EcloK995120.1$, $bla_EcloK99230$ 및 $bla_EareK9911729$)는 E. cloacae MHN1의 chromosomal ampC 유전자($bla_EcloMHN1$)와 99.6% 이상의 상동성을 나타냈으며 두 ampC 유전자($bla_Eclok9973$ and $bla_EcloK9914325$)는 E. cloacae 908R의 chromosomal ampC 유전자($bla_EcloQ9908R$)와 99.7% 상동성을 나타냈다. 이런 결과는 6개 ampC 유전자가 $bla_EcloMHN1$ or $bla_EcloQ9908R$로부터 유래되었음을 시산한다. 발현ㆍ분비 벡터를 이용하여 제조한 6개 transformant의 MIC값 양상 및 정확한 pI값은 E. coli 균주에 외부 유전자의 특성을 고찰하는 목적에 개발된 발현$.$분비 백터(pMSG1219)가 유용함을 의미한다.