- 期刊
CAMP試驗鑑定乙型鏈球菌的影響因素
An Examination of Factors Affecting CAMP Tests Used for the Identification of Streptococcus agalactiae
摘要
乙型鏈球菌(Streptococcus agalactiae, B群鏈球菌，GBS)可引起新生兒敗血症、腦膜炎與肺炎，也可引起產婦肺炎及敗血症，因此產前檢查GBS將有助於預防新生兒及產婦感染。GBS的鑑定方法中以CAMP試驗最常操作，但其試驗結果常受到各種因素影響，若稍不小心即容易發生偽陽性。本研究模擬CAMP試驗的各種可能影響因素進行評估，結果指出CAMP試驗最理想的操作方法為(i)測試菌與產生-lysin的Staphylococcusaureus (ATCC 25923，金黃色葡萄球菌)接種距離以5~7mm左右為最佳；(ii)測試的BAP(血平板)培養基厚度為3~4 mm以及不能太乾或濕度太高；(iii)測試BAP的培養環境，若在一般培養箱，其判讀時間為18~24小時，但若在5% CO_2培養箱則需在5~6小時判讀，若呈陰性則在一般培養箱繼續培養18~24小時；(iv)接種後的BAP置放室溫過久再培養於35℃，將會因冷熱交替而促進溶血反應，可能導致偽陽性以及(v)必須包括化膿性鏈球菌(Streptococcus pyogenes, GAS)標準株作為陰性對照，因其為最容易產生偽陽性的菌種。基於上述發現，吾等認為利用CAMP試驗鑑定GBS時，檢驗人員必須熟悉GAS及GBS菌落特徵的差異以及配合其它必要的鑑定試驗(如bacitracin及/或SXT感受性、PYR試驗等)，以免發生錯誤。
並列摘要
Streptococcus agalactiae, GroupBStreptococcus (GBS), can cause septicemia, meningitis, and pneumonia in newborns as well as pneumonia and septicemia in new mothers in the postpartum period. Therefore, testing pregnant women for GBS could prevent related infections both during pregnancy and following delivery. The Christie, Atkins, and Munch-Peterson (CAMP) test is one of the most common methods used for GBS identification; however, the results can be influenced by various factors. This study will simulate these factors and evaluate their potential for interfering with the test results. The results of the study indicated that the optimal procedure for the CAMP test involves (i) an inoculation distance between the test organism and -lysinproducing Staphylococcus aureus (ATCC 25923) of around 5-7 mm; (ii) a thickness of 3~4 mm blood agar plate (BAP) in which is neither too dry nor too wet; and (iii) an adequate incubation environment for the BAP with an ambient incubator, the interpretation time is fixed at 18~24 h after incubation. However, if test results are negative after 5-6 h in a 5% CO2 incubator, the BAP should be further incubated for 18-24 h. Furthermore, (iv) if the inoculated BAP is left at room temperature for too long before it is incubated at 35°C, hemolysis may be enhanced, creating a false-positive reaction due to the hot-cold lysis. Lastly, (v) the test must include Streptococcus pyogenes, Group A Streptococcus (GAS), as a negative control, as it commonly causes a false-positive CAMP reaction. Based on the above findings, we believe it is important to understand the differences in colony morphology between GAS and GBS and to utilize the combined results of other necessary test methods (e.g. bacitracin susceptibility, sulfamethoxazole-trimethoprim susceptibility, and the pyrrolidonyl arylamidase test) to avoid the misidentification of GBS.