MLSB계 항생물질 유도내성 세균에서 In vitro로 선발된 지속성 내성형 erm(A) and erm(C)의 분자적 특성 규명

Molecular Analysis of Spontaneous Mutations in erm(A) and erm(C) Selected In vitro as a Constitutive MLSB Resistant Staphylococci

The predominant macrolides-Lincosamide-Streptogramin B (MLSB) antibiotics resistance genes in staphylococci are erm(A) and erm(C). There is the phenomenon that the ratio of constitutively MLSB antibiotics resistance(cMLS) in erm(A) is much higher than in erm(C). Thus, we confirmed that the difference of the mutation ratio between erm(A) and erm(C) makes the phenomenon. We examined 8 staphylococci carrying inducibly expressed (iMLS)erm(A) and erm(C) genes. After overnight incubation in the presence of the non-inducer MLSB antibiotics, spontaneous mutants constitutively expressed MLSBresistance were selected. Against our expectation, the mutation ratio of erm(A) was lower than erm(C). Therefore, possibilities of other factors determining the ratio of cMLS phenotype might be concerned. All the mutants showed sequence alterations in translational attenuator and all the alterations seemed to give rise to change the second structure of mRNA to express constitutively. For erm(A), 4 different types of sequence deletions ranging from 72 bp to 122 bp and 3 different types of duplications ranging 24 bp to 93 bp were detected. Also, there were 9 different types of duplications ranging 15bp to 154bp in erm(C).