IMVC TESTS

ما هي فحوصات IMVIC كل فحص لوحده وصفات هذه الفحصات وبعض البكتيريا تقارن بهذه الفحوصات

هذه الكلمة هي مختصر او جمع لاربعة اختبارات تستخدم بصورة رئيسية في تشخيص العائلة المعوية وهي:
I:indol test
الكشف عن تكون الاندول, الوسط المستخدم هو ماء الببتون الكاشف هو كوفاكس
الوسط غني بالتربتوفان
النتيجة:+ظهور حلقة حمراء على سطح الوسط بعد اضافة الكاشف
-ظهور حلقة صفراء
M:methyl red الكاشف هو المثيل الاحمر الذي يضاف بعد التحضين
النتيجة:+تحول لون الوسط الى احمر وردي
-لون الوسط يصبح اصفر او لا يظهر لون احمر
VP:فحص فوكس بروس كاور
الكاشف 40%KOH
5%alpha naphthol
النتيجة:+ظهور لون احمر قرمزي بعد عدة دقائق من اضافة الكاشف
الوسط MR-VPيستخدم لاختبار المثيل الاحمر ولفوكس بروس كاور
Citrat:الكشف عن استهلاك السترات كمصدر وحيد للكاربون من قبل البكتريا
الوسط Simmons citrat والكاشف ضمن الوسط
النتيجة:+تحول لون الوسط الى ازرق
-عدم تغير لون الوسط الاخضر
E.coli In+ Mr+ post VP- Citrat:negative
Enterobacter aerogenes بالعكس تماما اي سالبة للاندول والمثيل الاحمر وموجبة لفوكس والسترات
وتقدر تجد معلومات وافية عن هذه الاختبارات في اي كتاب عملي للمايكروبايولوجي



MicroVision

IMViC
Enterobacteriaeae (enterics) are Gram-negative bacteria that grow in the intestinal tract of humans and other animals. The IMViC tests are frequently employed for identification of this group of microbes which includes such organisms as Klebsiella, Enterobacter, and Escherichia coli. The presence of E. coli is used by public health officials as an indicator of fecal contamination of food and water supplies. While Enterobacter and Klebsiella resemble E.coli in being lactose fermenters, their presence does not necessarily indicate fecal contamination because they are widespread in soil and grass. The IMViC tests can be used to differentiate these three organisms.

IMViC is an acronym that stands for indole , methyl red, Voges-Proskauer , and citrate . To obtain the results of these four tests, three test tubes are inoculated: tryptone broth (indole test), methyl red - Voges Proskauer broth (MR-VP broth), and citrate.

The Indole Test

The test organism is inoculated into tryptone broth, a rich source of the amino acid tryptophan. Indole positive bacteria such as Escherichia coli produce tryptophanase, an enzyme that cleaves tryptophan, producing indole and other products. When Kovac's reagent (p-dimethylaminobenzaldehyde) is added to a broth with indole in it, a dark pink color develops. The indole test must be read by 48 hours of incubation because the indole can be further degraded if prolonged incubation occurs. The acidic pH produced by Escherichia coli limits its growth.

The Methyl Red and Voges-Proskauer Tests

The methyl red (MR) and Voges-Proskauer (VP) tests are read from a single inoculated tube of MR-VP broth. After 24-48 hours of incubation the MR-VP broth is split into two tubes. One tube is used for the MR test; the other is used for the VP test.

MR-VP media contains glucose and peptone. All enterics oxidize glucose for energy; however the end products vary depending on bacterial enzymes. Both the MR and VP tests are used to determine what end products result when the test organism degrades glucose. E. coli is one of the bacteria that produces acids, causing the pH to drop below 4.4. When the pH indicator methyl red is added to this acidic broth it will be cherry red (a positive MR test).

Klebsiella and Enterobacter produce more neutral products from glucose (e.g. ethyl alcohol, acetyl methyl carbinol). In this neutral pH the growth of the bacteria is not inhibited. The bacteria thus begin to attack the peptone in the broth, causing the pH to rise above 6.2. At this pH, methyl red indicator is a yellow color (a negative MR test).

The reagents used for the VP test are Barritt's A (alpha-napthol) and Barritt's B (potassium hydroxide). When these reagents are added to a broth in which acetyl methyl carbinol is present, they turn a pink-burgundy color (a positive VP test). This color may take 20 to 30 minutes to develop. E. coli does not produce acetyl methyl carbinol, but Enterobacter and Klebsiella do.


The Citrate Test

The citrate test utilizes Simmon's citrate media to determine if a bacterium can grow utilizing citrate as its sole carbon and energy source. Simmon's media contains bromthymol blue, a pH indicator with a range of 6.0 to 7.6. Bromthymol blue is yellow at acidic pH's (around 6), and gradually changes to blue at more alkaline pH's (around 7.6). Uninoculated Simmon's citrate agar has a pH of 6.9, so it is an intermediate green color. Growth of bacteria in the media leads to development of a Prussian blue color (positive citrate). Enterobacter and Klebsiella are citrate positive while E.coli is negative.

Thus E.coli gives ++-- results on the IMViC tests, while Enterobacter and Klebsiella give the reverse: --++



indol test






methyle red





Voges-Preskauer




citrate