SURVEY OF THE MEC REGULATOR GENES IN CLINICAL ISOLATES OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 07807113
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: General surgery
• Research Institution: HIROSHIMA UNIVERSITY
• Principal Investigator: TAKESUE Yoshio Medical HOSPITAL,HIROSHIMA UNIVERSITY ASSISTANT PROFESSOR, 医学部・附属病院, 講師 (70197292)
• Co-Investigator(Kenkyū-buntansha): IMAMURA Yuuji Medical HOSPITAL,HIROSHIMA UNIVERSITY ASSOCIATE, 医学部・附属病院, 助手 (70274082)
• Project Period (FY): 1995 – 1996
• Keywords: nosocomial infection / antibiotic resistance / MRSA / gene / exotoxin / mec A / mec I / Southern hybridization

Research Abstract

The distribution of the mec regulator genes mec R1 and mec I were studied in methicillin resistant Staphylococcuc aureus (MRSA) clinical isolates collected in 1993 in the Hiroshima area. Coagulase types, enterotoxins production and toxic shock syndrome toxin-1 (TSST-1) production were determined in all 179 strains. 24strains which have various types of coagulase and enterotoxins production were selected and examined. All of the 24 strains hybridized with mec A and 5l-end region of the mec R1 by Southern hybridization using polymerase chain reaction (PCR) -amplified probes. These strains were diveded into two patterns of mec regulator genes ; one hybridized with all regulatory genes and another lacked 31-end region of the mec R1 and mec I from the halfway of mec R1 by Southern hybridization. Each group of strains classified by coagulase typing, enterotoxins and TSST-1 production had same pattern of mec regulator genes except coagulase IV enterotoxin A producing (IVA type) strains. Low methichillin MIC strains like strain N315 and high resistant strains were found in the strains which have all regulatory genes. The mec I gene of high resistant strains were found to harbor a point mutation, but the mecI gene of one of low methicillin MIC strains was the intact mec I gene. The basal level of mec A gene transcription was elevated in the strains which lack the mec I gene or carry point mutations in their mec I genes. These data suggested that the deletion and the mutation of the mec I gene which is the repressor on the mec A gene have important role for the methicillin resistance in clinical isolate of MRSA.But the inactivation of the mec I gene can not explain the mechanism of the high methicillin resistance.