Oligotrophic bacteria in ultra-pure water systems: Media selection and process component evaluations

Robert A. Governal, Moyasar T. Yahya, Charles P. Gerba, Farhang Shadman

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Presently, tryptic soy agar (TSA) medium is used in the semiconductor industry to determine the concentration of viable oligotrophic bacteria in ultra-pure water systems. Deionized water from an ultra-pure water pilot plant was evaluated for bacterial growth at specific locations, using a non-selective medium (R2A) designed to detect injured heterotrophic as well as oligotrophic bacteria. Results were compared to those obtained using Tryptic Soy Agar. Statistically greater numbers of bacteria were observed when R2A was used as the growth medium. Total viable bacterial numbers were compared both before and after each treatment step of the recirculating loop to determine their effectiveness in removing bacteria. The reduction in bacterial numbers for the reverse osmosis unit, the ion exchange bed, and the ultraviolet sterilizer were 97.4%, 31.3%, and 72.8%, respectively, using TSA medium, and 98.4%, 78.4%, and 35.8% using R2A medium. The number of viable bacteria increased by 60.7% based on TSA medium and 15.7% based on R2A medium after passage of the water through an in-line 0.2-μm pore size nylon filter, probably because of the growth of bacteria on the filter. Our results suggest that R2A medium may give a better representation of the microbial water quality in ultra-pure water systems and therefore a better idea of the effectiveness of the various treatment processes in the control of bacteria.

Original languageEnglish (US)
Pages (from-to)223-227
Number of pages5
JournalJournal of Industrial Microbiology
Issue number4
StatePublished - Nov 1991


  • Bacteria
  • Deionized water
  • Oligotroph
  • Ozone
  • R2A medium
  • Ultra-pure water
  • Ultra-violet sterilization

ASJC Scopus subject areas

  • Applied Microbiology and Biotechnology


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