Iron Reducing Bacterial Broth
Iron Reducing Bacterial Broth has been designed for the detection of iron reducing bacteria following the NACE standard (TMO194-2014). It is an anaerobic yellow media that will turn turbid and green if iron reducing bacteria are actively present. IRB has become a very popular media due to the proliferation of iron reducing bacteria in many oil and gas systems affected by microbiologically influenced corrosion.
Frequently Asked Questions
1-I have ordered many batches of IRB of different TDS percentages and they look a little bit different from each other. Why is that?
Due to high concentration of salt and other chemicals, higher percentages will look more turbid and with a precipitant forming at the bottom of the vial. Regardless of these visual differences, IRB will provide the ideal conditions for the bacteria growing in each of the TDS percentages.
2-After inoculating some IRB vials, the media has turned dark, almost black, instead of green. Why is that?
There are some things to consider when working with IRB. Iron reducing bacteria will turn the media green due to their metabolism. It could go from light green, almost turquoise, to a very dark green. However, if the media turns almost black after being inoculated and incubated, there is a possibility of a very high concentration of SRB. Sulfate reducing bacteria can interact and work very closely with iron reducing bacteria under certain conditions. IRB media is very nutritious and some ingredients can be used by SRB to proliferate and secrete enough H2S that will react with the iron dissolved in the media, and forming the black precipitant very characteristic of SRB. In order to minimize this, it is recommended to keep inoculated IRB vials no longer than two weeks inside an incubator. If the media turns immediately black it means there is a high concentration of H2S already in the system and other measures probably need to be taken. It is recommended to do a side by side inoculation of IRB with MPB or API in order to determine how predominant is the concentration of sulfate reducing bacteria in the system.
3- Is IRB sensitive to oxygen?
IRB is manufactured under anaerobic conditions but it can tolerant small amounts of oxygen. However, if it is exposed to oxygenic condition for a prolonged period the time, the media could start turning orange on its own.
4-How can I know if the media is contaminated with microorganisms other than iron reducing bacteria?
The media will only turn green if there is iron reducing bacteria actively present. If there is a significant amount of SRB the media could potentially turn dark grey or black. Any other kind of bacteria won’t show any color change, and they’ll only turn the media turbid.