MEDIA FOR THE DETECTION OF SULFIDE-PRODUCING BACTERIA IN INDUSTRIAL WATER-SYSTEMS

The importance of sulphate-reducing bacteria (SRB) in microbiological induced corrosion (MIC) has been widely recognized for many years [1]. There are many formulations of culture media used for enumerating SRB [2,3]. Previous studies indicated that viable count procedures undere stimated the in situ population by a factor of approximately 1000 comp ared to in situ sulphate reduction activity [1,4]. The aim of this stu dy was to evaluate different isolation media and carbon sources for th e isolation and detection of SRB in South African industrial water sys tems. Modified iron sulphite (IS) medium yielded the highest numbers w hen used to enumerate SRB from pure cultures and industrial water samp les. When comparing API, SABS, IS, Oxoid and modified synthetic medium using pure cultures of Desulfovibrio desulfuricans IS-medium gave a 1 2.1%, 40%, 53.3% and 60.3% higher recovery than SABS-, Postgate-, API- and synthetic medium, respectively (p <0.05). IS-medium gave a 20.1%, 61.8% and 100% higher recovery than SABS-, API- and Oxoid medium, res pectively, when using pure cultures of Desulfotomaculum orientis (p <0 .05). The dominant sulphide-producing bacteria isolated from the indus try using IS-medium were facultative aerobic gram-negative rods that w ere able to produce sulphide from sulphite under strictly anaerobic co nditions. IS-medium was therefore not selective for SRB only. H2S-prod ucing bacteria that utilized lactate, acetate, formate or palmitic aci d as different carbon sources were also isolated from industrial water samples when using synthetic medium.