| 摘要: | Oxacillin Resistant Staphylococcus aureus (簡稱ORSA)，是院內感染的重要致病性細菌。由於該類細菌常具多重抗藥性質，及易受環境變化所影響，因此，臨床實驗室對於該菌的分離，常需特別的注意，以避免錯誤的結果發生，造成治療與感染管制失敗。我們分析了1993年元月至1997年12月止， 本校附設醫院所發現的ORSA 感染的檢體共1939 件。並使用Oxacillin， Penicilin， Cephalothin， Cephamandole， Ceftaxime， Imipeneme，Vancomycin，Erythromycin，Tetracycline， Gentamicin， Clindamycin， Norfloxacin等12種抗生素， 進行Disc diffusion method的藥物感受性試驗。並比較在含2%， 4%，6% NaCl與不含鹽類的Mueller-Hinton培養基，ORSA對抗各種抗生素的抑制狀況，及評估流行病學調查使用的 Antibiogram Resistance Typing ( A R type )。結果發現5年來ORSA抗藥情形都有普遍上升傾向。治療方面仍以Vancomycin 最具療效。本篇文章將AR type 歸類， 可分 81 組，其中Type 1的全抗性是佔第一位(40.8%) 。即Vancomycin有效外， 所有抗生素皆顯示抗性。 分析鹽濃度對抗生素感受性試驗的影響。結果發現-lactam抗生素都具有Heterogeneous resistant的表現型，特別是Cephalothin
(92.0 %) 最多。而non--lactam抗生素方面，則皆為Homogeneous
resistant， 抑制圈呈抗性， 無變化。為進一步瞭解這些現象的發生機制，我們就其中的幾種抗生素Cephalothin， Imipenem及Penicilin進行在各種鹽濃度下，以進行抑菌試驗抑制菌生長百分之50的濃度(IC 50)測試。証明產生的抑制圈變化與抗生素種類， 劑量及培養基內含鹽有關。因此認為ORSA 在執行Disc diffusion method 的 susceptibility test 時， 使用的Mueller-Hinton plate 以不加 NaCl 為最適宜 。
Oxacillin Resistant Staphylococcus aureus (ORSA) is one of the important hospital infection agents. This bacterial strain frequently carries resistance determinants to many different antibiotics. However, their resistnace characteristics are variously measured due to the detection conditions. Therefore, cares should be taken to isolate the strain clinically
in order to make an accurate diagnosis, and subsequently a suitable
treatment and infection control will then be possible. In this thesis study,
we have analyzed 1,939 ORSA isolates found in Chung Shan Medical College Hospital from January, 1993 to December, 1997. Twelve
antibiotics, including oxacillin, penicillin cephalothin, cephamandole, ceftaxime, imipeneme, vancomycin, erythromycin, tetracyclin,
gentamicin, clindamycin and norflorxacin, were used to measure the drug susceptibility of those 1,939 ORSA isolates using disc diffusion method. Additionally, we have compared their drug susceptibilities using Mueller-Hintone medium in the presence of 0%, 2%, 4%, 6% of sodium chloride
as well as their Antibiogram Resistance Typing (AR type) were also determined. We found the drug resistance in these ORSA isolates was increased in recent years. Vancomycin is still the best choice for those
drug-resistant ORSA. In this thesis, 81 groups of AR types were found. Among them, type 1 (40.8%) is the most drug resistant strain, resistance
to almost every drugs tested in this study, and vancomycin will be the
drug of choice for the bacterial infection. In the presence of sodium
chloride, a heterogeneous resistance phenotype was found among those
-lactam drugs used in the assays, especially when cephalothin was used
(92.0%). However, the phenotype was not found when those non--
lactam antibiotics were used in the assays. To further understand the mechanism for the phenomena, we determined the IC50 for cephalothin, imipenem and penicillin in the presence of different concentrations of
sodium chloride. Our results have demonstrated that the inhibition
phenotype changed are related to only certain types of drug and the
presence of sodium chloride. Thus, we concluded that no need for sodium chloride in the susceptibility test when using disc diffusion method in
Mueller-Hinton plate. |
