Naegler’s reaction is given by –
**Core Concept**
Naegler's reaction is a diagnostic test used to identify the presence of _Acanthamoeba_ species, which are free-living amoebae that can cause granulomatous amoebic encephalitis (GAE) in humans. This reaction involves the detection of the enzyme cysteine proteinase, which is produced by _Acanthamoeba_.
**Why the Correct Answer is Right**
The Naegler's reaction involves the incubation of a clinical sample with a substrate that contains cysteine, resulting in the formation of a brown pigment due to the action of cysteine proteinase. This enzyme is produced by _Acanthamoeba_ and is responsible for the degradation of cysteine-containing proteins. The formation of the brown pigment indicates a positive Naegler's reaction, confirming the presence of _Acanthamoeba_ in the sample.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not related to the Naegler's reaction or _Acanthamoeba_ detection.
**Option B:** This option is incorrect because it refers to a different diagnostic test, such as the indirect immunofluorescence assay (IFA), which is used to detect other types of pathogens.
**Option C:** This option is incorrect because it is a different enzymatic reaction, such as the Elastase test, which is used to detect other types of pathogens.
**Clinical Pearl / High-Yield Fact**
It is essential to note that _Acanthamoeba_ can cause GAE in immunocompromised individuals, such as those with HIV/AIDS or cancer patients undergoing chemotherapy. Therefore, a positive Naegler's reaction should prompt further investigation and treatment to prevent the progression of the disease.
**Correct Answer:** Not provided in the question.