靛基質（Indole）試驗：

　　某mou些xie細xi菌jun能neng分fen解jie蛋dan白bai腖dong中zhong的de色se氨an酸suan，生sheng成cheng吲yin哚duo。吲yin哚duo的de存cun在zai可ke用yong顯xian色se反fan應ying表biao現xian出chu來lai。吲yin哚duo與yu對dui二er甲jia基ji氨an基ji苯ben醛quan結jie合he，形xing成cheng玫mei瑰gui吲yin哚duo，為wei紅hong色se化hua合he物wu。

　　試驗方法：將待試純培養物小量接種於試驗培養基管
，於36±1C培養24h時後，取約2ml培養液，加入Kovacs氏試劑2~3滴(di)
，輕(qing)搖(yao)試(shi)管(guan)，呈(cheng)紅(hong)色(se)為(wei)陽(yang)性(xing)，或(huo)先(xian)加(jia)少(shao)量(liang)乙(yi)醚(mi)或(huo)二(er)甲(jia)苯(ben)

，搖(yao)動(dong)試(shi)管(guan)以(yi)提(ti)取(qu)和(he)濃(nong)縮(suo)靛(dian)基(ji)質(zhi)，待(dai)其(qi)浮(fu)於(yu)培(pei)養(yang)液(ye)表(biao)麵(mian)後(hou)，再(zai)沿(yan)試(shi)管(guan)壁(bi)徐(xu)緩(huan)加(jia)入(ru)Kovacs氏試劑數滴
，在接觸麵呈紅色，即為陽性。

　　實驗證明靛基質試劑可與17種不的靛基質化合物作用而產生陽性反應，若先用二甲苯或乙醚等進行提取，再加試劑，則隻有靛基質或5-甲基靛基質在溶劑中呈現紅色，因而結果更為可靠。

Margaret (Peg) Johnson, Mesa Community College, Mesa, Ariz., USA

　　This image depicts the results of negative and positive indole tests. The indole test is frequently employed to distinguish Klebsiella or Enterobacter bacteria (indole negative) from Escherichia coli (indole positive). The presence of E. coli is used by public health officials as an indicator of fecal contamination of food and water supplies.

　　Prior to this test, Enterobacter aerogenes was used to inoculate one tryptone broth, while another tryptone broth was inoculated with Escherichia coli. The two broths were then incubated for 24 h and mixed with Kovas reagent (p-dimethylamino-benzaldehyde). Tryptone broth is rich in the amino acid tryptophan. Tryptophanase, an enzyme, is capable of cleaving tryptophan and producing indole, pyruvic acid, and ammonia. Indole can be detected by the development of a red color after adding Kovas reagent. Organisms that do not produce tryptophanase will be indole negative, as no indole will be present to react with the Kovas reagent.