Antibiogram Patterns of Staphylococcus aureus Isolates and Molecular Typing of MRSA Isolates from an Hospital in Andong City Using the Coagulase PCR-RFLP Method

Kim, Shin; Kim, Sang Yun; Woo, Yong Ku; Kim, Eun Hee

Abstract

BACKGROUND: Up to date the antimicrobial resistance of Staphylococcus aureus (S. aureus) have been increased. The antimicrobial resistance patterns of Korean S. aureus strains were varied according to their isolated regions, periods, and treated method, etc. Recently methicillin-resistant S. aureus (MRSA) has already appeared one of the important nosocomial pathogens and also established the endemicity among many large scale hospitals in Korea. So far the animicrobial resistance of S. aureus isolates and MRSA isolation rates in the Andong city have been not reported yet. Therefore, it is necessary to know how many MRSA exist in one of the hospitals in Andong city. The aim of this study is to investigate the antibiogram patterns of S. aureus isolates and to differentiate the genetic relatedness among the MRSA strains using the coagulase gene product PCR-RFLP method from an hospital in Andong city over 2 years period from 1999 to 2000.
METHODS
S. aureus isolates from various clinical specimens were collected from one of the hospitals in Andong city during 2 years period from 1999 to 2000. The identification of S. aureus was carried out according to the biochemical and polymerase chain reaction (PCR) method. The antimicrobial susceptibility test was carried out according to the method of NCCLLS. Methicillin resistance was tested by both MIC (microdilution method) method of NCCLLS and mecA gene PCR. The molecular typing of MRSA strains was performed by coagulase PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) using the restriction enzyme (Alu I).
RESULTS
One hundred fifteen S. aureus isolates were cultured from clinical specimens. Antimicrobial susceptibility test and mecA gene PCR showed that 61.4% of S. aureus isolates were identified as MRSA strains. All MRSA isolates had more than 5 drug resistance patterns. But only 34.1% (15/44) of methicillin-susceptible S. aureus (MSSA) strains had established resistence to more than 4 drugs. Depending on the results of coagulase PCR-RFLP for MRSA strains, a total of 5 genetic types were discriminated with according to the DNA band size and number. Type A and B were generally the major genetic types, which were accounted for 71.4% (50 strains) and 15.7% (11 strains), respectively and other types were isolated only in small numbers.
CONCLUSIONS
MRSA strain has already been prevalent in an hospital in Andong city because 61.4% of S. aureus (70/114) isolates were typed as a MRSA strain. As the results of coagulase PCR-RFLP, type A and B were determined as a most predominant clones in this area. It is presumed that they have already been isolated from clinical specimens continuously and also established the endemicity in this area hospital. According to the diseases prevention and control strat-egy, it is necessary to block the spread of dominant MRSA clones and to study the transmission routes of dominant MRSA clones. The coagulse PCR-RFLP technique was an useful molecular typing tool for the MRSA isolates with no difficulty in manipulation.