[Detection of methicillin-resistant Staphylococcus aureus using PCR and non-radioactive DNA probes: IV. Mutational sequences in the region upstream of the mec A gene in clinical staphylococcal strains].
Expression of mec A is regulated by two regulatory genes (mecR1 and mecI); the intact regulatory genes exist in the N315 strain of methicillin-sensitive S. aureus, whereas the repressor gene (mecI) is deleted in the MR108 strain of methicillin-resistant S. aureus (MRSA). However, our previous findings that clinical strains of N315 type were methicillin-resistant suggest possible mutations within the operator region, by which the inhibitory effect of MecI is released to induce the constitutive expression of mec A. Therefore, we analyzed nucleotide sequences in the region upstream of the mec A gene and in the regulatory genes, by using PCR-direct sequencing and ASO probes. Analysis of selected clinical strains by ASO probes revealed that 74% of MRSA and 36% of MRSE (methicillin-resistant S. epidermidis) lacked the mecI gene whereas 26% of MRSA and 64% of MRSE possessed the intact regulatory genes. Furthermore, PCR-direct sequencing identified four different mutations in the operator nucleotide sequence and one mutation in Shine-Dalgarno sequence. Additionally, these mutations were shown to occur in the strains of N315 type with higher probability rather than in those of MR108 type. The data suggest that one or more of these mutational sequences at least may have some influence on the expression of methicillin-resistance in clinical staphylococcal strains.
Clinical Laboratory, Hyogo College of Medicine, Nishinomiya.
K
K
Yamashita
Y
Y
Takarada
T
T
Muto
N
N
Otsuka
S
S
Kagawa
A
A
Matsuoka
D001483:Base Sequence; D015342:DNA Probes; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016106:Methicillin Resistance / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D009875:Operator Regions, Genetic; D016133:Polymerase Chain Reaction; D017421:Sequence Analysis; D013211:Staphylococcus aureus / Q000235:genetics* / Q000302:isolation & purification
D015342:DNA Probes