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KMID : 0352819920080020105
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Kosin Medical Journal
1992 Volume.8 No. 2 p.105 ~ p.134
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Growth Patterns of Methicillin resistant Staphylococcus aureus in -Lactam Antibiotic Containing Muller-Hinton Broth
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Abstract
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Methicllin-resistant Staphylococcus aureus(MRSA) has become a major pathogen in patients with nosocomial or community-acquired infections.
In the present study, we examined the minimum inhibitory concentration(MBC) of methicllin, oxacillin, cefatrizine and tetracycline on MRSA, then followed growth patterns of MRSA and formation of L-form at the respective MIC for various
strains
to
elucidate the mechanism of paradoxic effect of penicillin antibiotics on MRSA.
@ES Following results were obtained
@EN 1. In twenty strains of MRSA, the MBC of methicillin equal to MIC was 15%, the MBC two fold greater than MIC was 60%, the MBC three fold greater than MIC was 20% and the MBC four greater than MIC was 20%.
2. With oxacillin, the MBC with equal to MIC was 10%, the MBC twofold greater than MIC was 50%, the MBC three fold greater than MIC was 20% and the MBC four fold greater than MIC was 20%. 3 With cefatrizine, the MBC with equal to MIC was
10%,
the
MBC two fold greater than MIC was 60%, the MBC three fold greater than MIC was 20% and the MBC four fold greater
than MIC was 10%.
4. With tetaracycline, the MBC with equal to MIC was 10%, the MBC two fold greater than MIC was 55%, the MBC three fold greater than MIC was 25% and the MBC four fold greater than MIC was 5%.
5. In all strains of MRSA showing a paradoxical effect of methicillin, growth was significantly more with 0.5×MIC than with 1 xMIC in using Muller-Hinton.
6. In some strains of MRSA, the paradoxical effect of methicillin, growth was significantly more with 0.5×MIC in the 50% serum containing Muller-Hinton broth.
7. The paradoxical effects of oxacillin and cefatrizine occurred at 1×MIC in Muller-Hinton broth and at 0.5×MIC in 50% serum containing Muller-Hinton broth.
8. With tetracycline, the paradoxical effect was not observed both in Muller-Hiton broth and 50% containg Muller-Hinton broth.
9. MRSA strains formed L-form in the media containing 0.5×IC of methicillin, oxacillin, cefatrizine containg agar, but not in tetracycline containing agar.
These results indicate in some strains of MRSA paradoxical effects of methicillin, oxacillin, and cefatrizine can be observed at 0.51×MEC, and this is due to the formation of L-form bacteria.
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KEYWORD
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