Color measurement as a means of quantifying surface biofouling

Laboratory reactors fitted with removable ceramic porcelain growth surfaces were inoculated with a consortium of biofilm forming environmental isolate s. A Minolta colorimeter CR-200 (Minolta Camera Co., Ltd, Ramsey, NJ) was u sed in conjunction with a specially designed adapter to evaluate the reflec tive color of the porcelain disks as biofilm accumulated on them. Areal via ble cell counts were monitored over a period of eleven days in two separate experiments and direct color measurements of the untreated, microbially fo uled test surfaces were collected. This colorimetric assay was both non-des tructive and immediate. A strong linear relationship between log cell densi ty and log color change was observed. The Pearson product moment correlatio n coefficient for all 45 observations combined was r = 0.95. Separate regre ssion lines for each experiment were not significantly different (P = 0.19) . When adjusted for time, the (partial) correlation coefficient between log cell density and log color change was r = 0.87, which suggests that the re lationship between the two measures can not be explained by their mutual de pendence on time. Reflective color measurement provided a rapid, non-destru ctive and quantitative measure of biofilm accumulation. (C) 1998 Elsevier S cience B.V. All rights reserved.