Modified Postgate’s B

Modified Postgate’s B (MPB) is the NACE standard (TM0194-2014) media for the detection of sulfate reducing bacteria (SRB) in the oil and gas industry. MPB is a complex media manufactured and dispensed under strict anaerobic conditions. In contrast to other media designed for the detection of SRB, MPB has dissolved iron instead of an iron nail which facilitates and increases the growth rate of sulfate reducing bacteria. If positive, MPB will turn from a pale white color with a precipitant to a dark grey or black color due to the formation of iron sulfide as a result of bacterial metabolism.

 

Frequently Asked Questions

1- I noticed MPB is not the only media offered for SRB, what is the difference between MPB and API?

According to the NACE standard TMO194-2014, both MPB and API media are considered acceptable for SRB growth; however, there are a few differences between these two kinds of media. MPB has more carbon sources like lactate and acetate that will increase the chances of recovering more SRB species. API has only lactate as a carbon source, so it could limit the amount of SRB recovered from a system. MPB also has certain chemicals that will inactivate any amount of oxygen that could get inside the vial during inoculation, increasing the chance of a higher recovery rate. API does not contain these chemicals and the potential of some SRB dying during inoculation is higher. In contrast to API that has an iron nail as a main source of iron, MPB has iron already diluted in the media which makes it more accessible to SRB decreasing the time it takes a vial to turn positive. Regardless of which media is preferred, Biotechnology Solutions TX can guarantee both types of media to be high quality.

 

2-Is it possible for an MPB vial to turn positive by exposing it to oxygen?

No, a MPB vial will never turn black just by exposing it oxygen. The only mechanism that could turn a vial black is by SRB metabolic activity or by a high concentration of H₂S. Even other anaerobic bacteria that could potentially grow in this media will never turn it black since they won’t produce the necessary chemicals for the positive reaction to occur. If oxygen gets inside the vial, the media will turn pink or slightly purple for a short period of time until all the oxygen is consumed and inactivated inside the vial. However, expired vials have the potential of turning slightly yellow due to iron oxidation.

3-Can I incubate this media at high temperatures in order to mimic the conditions I have in my system?

Yes, MPB can be incubated at higher temperatures if needed. There are some SRB species that thrive under high temperatures so it is understandable to incubate them under conditions that mimic their natural habitat as closely as possible. Most chemicals will remain functional at high temperatures; however, at around 55°C some will become less effective causing the growth rate to slow down and even accelerating the expiration time of the vials. If you plan on changing the incubation parameters from the ones recommended by the manufacturer and NACE standards, please contact a Biotechnology Solutions TX representative to guide you during the inoculation and incubation processes.

4-I performed a serial dilution, but I noticed the color change skipped one vial. What does it mean?

There many factors that could cause a vial to skip the color change in a serial dilution. The most common ones we have encountered are human errors. Sometimes one vial is skipped unintentionally from the serial dilution, or there is either air left inside the syringe while inoculating a vial or residual biocide that could affect the growth of the first vials in a dilution series. There is also the possibility of a statistical anomaly, which means that all the bacteria got transferred from one vial to another without being diluted. To avoid this, we recommend being consistent with the mixing while performing a serial dilution.