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

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.

Competitive exclusion against Salmonella gallinarum of Salmonella enteritidis infected chickens

To evaluate the degree of competitive exclusion against Salmonella gallinarum(S. gallinarum) of Salmonella enteritidis(S. enteritidis) infected chickens, fifty-six, 4-week old Hyline layer suspected of S. enteritidis infection were challenged with S. gallinarum. All chickens were tested for S. enteritidis isolation using cloacal swabs and serum plate agglutination test using S. enteritidis Ag. before challenge and classified into four groups(SE isolated, SE nonisolated, SE seropositive and SE seronegative). None of the SE isolated and the SE seropositive groups died after challenge and the average weight gains were 245.5g and 254.6g, respectively. But in the SE nonisolated and the SE seronegative groups, mortality was 18.2% and 20.6% and the average weight gains were 150.1g and 111.2g. The incidence of reisolation of S. gallinarum of the SE isolated and the SE seropositive groups were 41.7% and 47.6% from liver, 33.3% and 47.6% from spleen and 8.3% and 14.3% from cecum, respectively, and the SE nonisolated and the SE seronegative group were 63.6% and 64.7% from liver, 84.1% and 88.2% from spleen and 47.7% and 52.9% from cecum. The serological response of the SE isolated and the SE seropositive groups hardly changed from 75.0 and 81.8% before challenge to 75.0 and 85.7% after. But, the other two groups were found to be significantly higher after challenge and increased from 0 and 18.2% to 100%. Consequently, S. enteritidis preinfected chickens were found to be significant different in terms of mortality, weight gain, reisolation of S. gallinarum and serological response compared to noninfected chickens. Moreover, our study shows that S. enteritidis infected chickens appear strong competitive exclusion against the colonization of S. gallinarum.