Describe the Methyl Red Test With Enterococcus Faecalis

As its name would imply, Enterococcus faecalis is a common bacterium in the human intestine. In healthy people it doesn't typically cause any problems. Patients with weakened or compromised immune systems, however, are more vulnerable, and E. faecalis can sometimes "take the opportunity" to colonize other regions of the body where it can actually become harmful, especially the bladder and urinary tract. The methyl red test is a technique often used to help identify bacteria that may be E. faecalis.

Significance

• While E. faecalis is a normal inhabitant of your gastrointestinal tract, patients whose immune systems aren't functioning properly —for example, people taking certain chemotherapy drugs to treat cancer—may be at risk for infections from bacteria like E. faecalis that wouldn't ordinarily pose any threat.
  In recent years, however, E. faecalis has become one of the leading causes of hospital-acquired infections. These cases are often difficult to treat because some strains of E. faecalis are resistant to many of the more common antibiotics. It's important to be able to identify E. faecalis if its presence is suspected in a sample.

Function

• Many bacteria produce energy through a process called fermentation that releases compounds like lactic acid or ethanol as waste products. Bacteria called mixed acid fermenters excrete a mix of acids like formic acid and lactic acid. Adding a pH indicator—a chemical that changes color in response to changes in pH—to a culture broth can help identify mixed acid fermenters, since these bacteria create acidic conditions.

Effects

• Methyl red is a pH indicator that turns red when added to low-pH solutions; in neutral solutions, on the other hand, it retains its yellow color. The test is fairly straightforward. Several drops of the chemical are added to two test tubes, one of which contains broth with the bacteria to be identified and the other is a control. If the solution turns a bright red color, the test is positive; if it turns yellow or orange, it is negative. E. faecalis tests positive for methyl red.

Benefits

• Methyl red can help identify unknown bacteria from a sample. E. coli, for example, tests positive for methyl red while Enterobacter aerogenes is methyl-red negative. The methyl red test can be used for E. faecalis as well.

Considerations

• Because all mixed-acid fermenters should test positive, methyl red is typically only one of a series of tests necessary to differentiate between bacteria. Knowing that a bacterium is methyl-red positive doesn't identify it as a specific species. Generally microbiologists will perform other tests in addition to methyl red to rule out other possibilities when identifying bacteria.