J Korean Soc Microbiol.  1997 Jun;32(3):275-284.

Distribution of mec Regulator Genes in Methicillin - Resistant Staphylococci

• Cho DT
• Lim DG
• Kim JM

Abstract

In order to understand the role of mec regulator genes in the evolution of methicillin-resistant S. aureus (MRSA), the distribution of the mec regulator genes among the 66 clinical isolates of MRSA was analysed. And also the correlation between gene mutation and degree of phenotypic expression of resistance was studied. Fifty strains carried whole mec regulator region, while the mecI gene and nearly half of the 3'-end of the mecR#l gene were deleted in fifteen strains. The mecRl MS gene was detected among all of the mecA carried strains, but the mecRl PB gene was carried by 77% of the MRSA strains. At least a portion of the 5'-end region of the mecRl gene was carried by all MRSA strains tested. Forty-seven strains were finally confirmed to have mecI gene and each mecI gene of above strains was sequenced for identification of the relationship between repressor function of mecI gene on mecA transcription and MIC level of methicillin. Point mutations were detected in 11 strains of 47 strains. In 8 strains, there was one nucleotide substitution (C to T at position 202) that produced a new termination codon at position 201. In 3 strains, one nucleotide substitution from G to T at position 43 caused an amino acid substitution from Val to Phe. The MIC of methicillin of strains carrying mutated mecI genes ranged 256 ug/ ml to 1024 ug/ml. Transcription level of amplified cDNA corresponding to mecA was determined by the method of RT-PCR of extracted RNA. Total RNA was extracted from two strains with mutated mecI gene and a strain with intact mecI gene. Deletional loss or the mutational inactivation of the mecI gene did not affect the level of mecA transcription. Role of mecI gene as a strong repressor function on mecA gene seemed to be skeptical.

MeSH Terms

Amino Acid Substitution
Codon, Terminator
DNA, Complementary
Genes, Regulator*
Methicillin Resistance
Methicillin*
Methicillin-Resistant Staphylococcus aureus
Point Mutation
RNA
Codon, Terminator
DNA, Complementary
Methicillin
RNA