The iron-related bacteria (IRB) are recognized as being those bacteria that are iron utilizing. The form of this utilization can range from simply a passive bioaccumulation in the slime (biofilm) growths through to active use in metabolism. This test specifically uses the ability of bacteria to use ferric and ferrous iron in many ways to create various reactions, some of which are colored. It is now understood that some of the IRB may be able to derive respiratory or energy functions out of the reduction (ferrous) to oxidation (ferric) manipulations which occur through the activity of the IRB.
Some bacteria that are not IRB also do form copious slimes. They can cause many of the problems commonly associated with IRB but tend to generate white, grey, beige or black forms of slime rather than the browns. Under the right cultural conditions, many aerobic bacteria will generate slimes. The selective medium used in the SLYM-BART specifically encourages the formation of slimes. These are commonly seen as condensed cloudy/plate-like growths suspended in the liquid medium, gel-like rings (around the ball) or globular/swirl forms of slime in the basal cone. This group is known as the slime-forming bacteria.
Bacteria that are able to reduce sulfate to sulfide are often associated with corrosion (H2S electrolytic), odor problems ("rotten" egg) and black water. This test uses a medium selective for the SRB and provides a source of iron so that the black iron sulfides are produced when the SRB are active. To improve the selectivity of this test, the liquid medium is manipulated to generate an anaerobic (reductive) state that restricts growth to a narrow spectrum of anaerobes.
EMSL Test Codes:
Iron-Related Bacteria (IRB) - M121
Sulfate-Reducing Bacteria (SRB) - M122
Slime-Forming Bacteria (SLYME) - M123
Biofilm-Associated Bacteria (Group test for IRB, SRB, SLYME) - M125
Sample retention time - 1 week