Results on SRB-BART show a pink ring around the ball and some cloudiness in the culturing media under the ball. How should this be interpreted?
Pink ring on SRB-BART
It is negative for sulfate-reducing bacteria (SRB; i.e. no black base or black ball/top reaction). The pink ring (1) most commonly relates to the bacterial genera Chromobacterium, Flavobacterium, or Serratia forming a pink to red pigment usually at the interface between the ball and the surface of the culturing medium Clouding (2) is common when there is growth of anaerobic (fermentative) bacteria able to utilize some of the nutrients within the BART tester. In the SRB BART these events would be considered negative for the sulfide producing bacteria The only other bacteria that may generate pinks (most likely as reds to purples) are purple sulfur bacteria that can sometimes be detected in waters that are very reductive with high sulfur content. Clouding as described is extremely common and the manufacturer’s experience is that most SRB tests on natural water samples will show these types of reactions while the pink product reaction is rare (<5%). In the development of the SRB tester it has been found to be the most effective for separating the two major groups of hydrogen sulfide generators using either sulfates or sulfur-amino acids.