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Comparison of Plate Counts, Petrifilm, Dipslides, and Adenosine Triphosphate Bioluminescence for Monitoring Bacteria in Cooling‐Tower Waters
Effective bacterial control in cooling‐tower systems requires accurate and timely methods to count bacteria. Plate‐count methods are difficult to implement on‐site, because they are time‐ and labor‐intensive and require sterile techniques. Several field‐applicable methods (dipslides, Petrifilm, and adenosine triphosphate [ATP] bioluminescence) were compared with the plate count for two sample matrices—phosphate‐buffered saline solution containing a pure culture of Pseudomonas fluorescens and cooling‐tower water containing an undefined mixed bacterial culture. For the pure culture, (1) counts determined on nutrient agar and plate‐count agar (PCA) media and expressed as colony‐forming units (CFU) per milliliter were equivalent to those on R2A medium (p = 1.0 and p = 1.0, respectively); (2) Petrifilm counts were not significantly different from R2A plate counts (p = 0.99); (3) the dipslide counts were up to 2 log units higher than R2A plate counts, but this discrepancy was not statistically significant (p = 0.06); and (4) a discernable correlation (r 2 = 0.67) existed between ATP readings and plate counts. For cooling‐tower water samples (n = 62), (1) bacterial counts using R2A medium were higher (but not significant; p = 0.63) than nutrient agar and significantly higher than tryptone‐glucose yeast extract (TGE; p = 0.03) and PCA (p < 0.001); (2) Petrifilm counts were significantly lower than nutrient agar or R2A (p = 0.02 and p < 0.001, respectively), but not statistically different from TGE, PCA, and dipslides (p = 0.55, p = 0.69, and p = 0.91, respectively); (3) the dipslide method yielded bacteria counts 1 to 3 log units lower than nutrient agar and R2A (p < 0.001), but was not significantly different from Petrifilm (p = 0.91), PCA (p = 1.00) or TGE (p = 0.07); (4) the differences between dipslides and the other methods became greater with a 6‐day incubation time; and (5) the correlation between ATP readings and plate counts varied from system to system, was poor (r 2 values ranged from <0.01 to 0.47), and the ATP method was not sufficiently sensitive to measure counts below approximately 10 4 CFU/mL.
Comparison of Plate Counts, Petrifilm, Dipslides, and Adenosine Triphosphate Bioluminescence for Monitoring Bacteria in Cooling‐Tower Waters
Effective bacterial control in cooling‐tower systems requires accurate and timely methods to count bacteria. Plate‐count methods are difficult to implement on‐site, because they are time‐ and labor‐intensive and require sterile techniques. Several field‐applicable methods (dipslides, Petrifilm, and adenosine triphosphate [ATP] bioluminescence) were compared with the plate count for two sample matrices—phosphate‐buffered saline solution containing a pure culture of Pseudomonas fluorescens and cooling‐tower water containing an undefined mixed bacterial culture. For the pure culture, (1) counts determined on nutrient agar and plate‐count agar (PCA) media and expressed as colony‐forming units (CFU) per milliliter were equivalent to those on R2A medium (p = 1.0 and p = 1.0, respectively); (2) Petrifilm counts were not significantly different from R2A plate counts (p = 0.99); (3) the dipslide counts were up to 2 log units higher than R2A plate counts, but this discrepancy was not statistically significant (p = 0.06); and (4) a discernable correlation (r 2 = 0.67) existed between ATP readings and plate counts. For cooling‐tower water samples (n = 62), (1) bacterial counts using R2A medium were higher (but not significant; p = 0.63) than nutrient agar and significantly higher than tryptone‐glucose yeast extract (TGE; p = 0.03) and PCA (p < 0.001); (2) Petrifilm counts were significantly lower than nutrient agar or R2A (p = 0.02 and p < 0.001, respectively), but not statistically different from TGE, PCA, and dipslides (p = 0.55, p = 0.69, and p = 0.91, respectively); (3) the dipslide method yielded bacteria counts 1 to 3 log units lower than nutrient agar and R2A (p < 0.001), but was not significantly different from Petrifilm (p = 0.91), PCA (p = 1.00) or TGE (p = 0.07); (4) the differences between dipslides and the other methods became greater with a 6‐day incubation time; and (5) the correlation between ATP readings and plate counts varied from system to system, was poor (r 2 values ranged from <0.01 to 0.47), and the ATP method was not sufficiently sensitive to measure counts below approximately 10 4 CFU/mL.
Comparison of Plate Counts, Petrifilm, Dipslides, and Adenosine Triphosphate Bioluminescence for Monitoring Bacteria in Cooling‐Tower Waters
Mueller, Sherry A. (author) / Anderson, James E. (author) / Kim, Byung R. (author) / Ball, James C. (author)
Water Environment Research ; 81 ; 401-406
2009-04-01
6 pages
Article (Journal)
Electronic Resource
English
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