Introduction of MGP test
MGP stands for methyl-α-D-glucopyranoside. MGP test is effective for species identification of Enterococcus. Enterococcus gallinarum and Enterococcus casseliﬂavus are MGP test positive while Enterococcus faecalis and Enterococcus faecium negative. Vancomycin-resistant Enterococcus faecium (VREF) is a serious nosocomial problem which is difficult to differentiate from Enterococcus gallinarum and Enterococcus casseliﬂavus, while not important for purposes of control of nosocomial infections, show intrinsic resistance to vancomycin due to the vanC gene. Another side, E. gallinarum and E. casseliﬂavus are difﬁcult to differentiatefrom VREF by conventional biochemical tests, since they are phenotypically closely related. Therefore,MGP test is useful in preventing the misidentiﬁcation of vancomycin-resistant E. gallinarum as VREF for laboratories that cannot perform the rapid tube motility test. It is an alternative to the motility test. Typically, E. gallinarum and E. casseliﬂavus can be differentiated from E. faecium based on motility: E. gallinarum and E. casseliﬂavus are motile, while E. faecium is non motile.
Principle of MGP test
MGP broth is useful to differentiate enterococci based on the ability to acidify the carbohydrate MGP. Phenol red indicator present in medium that helps to identify the organisms on the basis color development i.e. development of yellow color, MGP test positive where as red or orange negative.
Requirements for test
Procedure of MGP test
- With the help of inoculating needle, Inoculate the MGP broth by lightly touching a single, isolated colony.
- Do not use a heavy inoculum.
- Incubate aerobically at 35°C for 24 hours.
- Observe for development of yellow color change in the medium.
MGP test Positive: Development of a yellow color acidiﬁcation of MGP
MGP test Negative: Red or orange color
E. gallinarum ATCC 49573: MGP test Positive
E. faecalis ATCC 29212: MGP Negative
- A heavy inoculum may give false-positive result.
- Longer incubation times may result in false-positive reactions.
- The test has reported sensitivity of 98-100% and a speciﬁcity of 95%
- Enterococcus vagococcus gives a positive result.
- Cowan and Steel’s ,manual for the identification of medical bacteria
- Lynne S. Garcia ,Clinical Microbiology Procedures Handbook