Molecular Genetic Study on Methicillin-Resistant Staphylococci Using Polymerase Chain Reaction of mecA and mec Related Hypervariable Region DNA

Kim, Min Jung; Oh, Yang Hyo

Abstract

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) are becoming increasingly responsible for the outbreaks of nosocomial infections around the world. Because MRSA are often resistant to antimicrobial agents and because of the current necessity to use non-beta-lactam antimicrobial therapy, infections with these organisms are difficult to treat. The purpose of this study was to explain how the genetic background contributes to the phenotypic expression of MRSA and to enable immediate and proper identification of MRSA in nosocomial infections.
METHODS
A total of 240 staphylococci strains were tested for epidemiological research. The molecular genetic methods, such as dot blot hybridization, polymerase chain reaction, and southern blot hybridization, were compared in terms of the immediate and proper identification of the pathogens. The arrangement of dru sequence, the repeat unit of genes, was clarified particularly through mecA probe to compare and distinguish the isolated MRSA strains.
RESULTS
By the dot blot hybridization, the mecA gene was detected in 120 MRSA strains and in 8 of 50 methicillin-suscpetible S. aureus (MSSA) in Group II (resistance to methicillin is induced in vitro). Among isolates included in Group I (resistance to methicillin is not induced in vitro) mecA genes were not detected. By PCR, the amplified DNA band of 533 bp was confirmed in 120 MRSA but not in MSSA. By the southern blot hybridization, the signal of the amplified electrophoresis band in PCR was similarly observed. The amplified band of mec related hypervariable region was observed in all methicilin resistant (MR) staphylococci but not in MSSA. The size of PCR products was between 194 bp and 1,353 bp. mec-related HVR was classified into seven genotypes. The nucleotide sequence of genotype E was similar to that of mec related HVR and eight units were directly repeated.
CONCLUSION
Both methods allowed rapid detection of mecA gene. Further differentiation of MRSA and other staphylococci strains was possible by PCR detection of polymorphism of HVR sequence which would be useful in tracing back the source of resistant clones.