THE MEASUREMENT OF CHLORINE ACTIVITY IN BIOFILM CONTAMINATED DENTAL UNIT WATER LINES

Potentially pathogenic microorganisms may participate in the formation of microbial biofilms on the interior walls of the plastic tubing use d to supply coolant and irrigating water in dental units. A program wa s designed to test the effect of diluted commercial bleach (5.25% sodi um hypochlorite) on bacteria colonizing dental unit water lines. A bas eline bacteriological assay was performed on 24 dental units located a t four separate institutional dental clinics located in the same metro politan area. Twelve units at three clinics (designated Clinics I, II, and III) had been treated once weekly with 1:10 NaOCl for periods ran ging from 6 mo to 6 yr. Twelve units at Clinic IV, which had never bee n treated with hypochlorite, were selected for a 28-day study of the e ffectiveness of two dilutions (1:10, 1:100) of 5.25% sodium hypochlori te for control of biofilm growth in dental water Lines. Eight units we re treated weekly with either 1:10 or 1:100 solutions of commercial bl each. The four control units were treated only with sterile deionized water. The eight units at Dental Clinics I and II had relatively low l evels of planktonic bacterial colony forming units/ml (CFU/ml) ranging from 0 to 8.8 x 10(3) CFU/ml with a mean of 1.1 x 10(3) CFU/ml (5 of 8 units had 0 CFU/ml and two had only 30 CFU/ml). Characteristic profi le curves were produced when chlorine concentration (ppm) was plotted versus a cumulative volume of solution hushed through the units. The c hlorine concentration showed very little initial change, then rapidly fell to zero as the solutions were flushed from the units with sterile deionized water. The total chlorine mass recovered at these clinics v aried from 94 to 101.7%, with the average being approximately 96%. Whe n chlorine concentration was plotted against the total volume of efflu ent recovered (including diluent), a characteristic chlorine profile c urves resulted which was dubbed a Type I Curve. Planktonic bacteria co unts at Clinics III and IV were much higher (Clinic III range: 1 x 10( 2) CFU/ml to 4.8 x 10(5) CFU/ml, median: 1.0 x 10(4) CFU/ml; Clinic IV range: 5.6 x 10(4) CFU/ml to 1.1 x 10(6) CFU/ml, mean: 4.7 x 10(5) CF U/ml), suggesting high levels of biofilm contamination. The chlorine r ecovered from Clinics III and IV varied from 40 to 88% with the averag e being 80%. The chlorine profile curves for the units at Clinics III and IV initially fell very rapidly, then more slowly as sterile distil led water was used to flush residual hypochlorite from the lines throu ghout the dilution flush phase of the treatment. These curves were cal led Type II Curves. The difference in the two profile curves may be du e to absorption and reaction of the available chlorine by adherent bio films. At the conclusion of the 28-day treatment of Clinic IV units, t he average percent chlorine recovered for the 1:10 NaOCl group increas ed to 99.7% and the profile curves yielded the same characteristics as those observed for Clinics I and II, suggesting low levels of microbi al contamination. Although each subsequent treatment of units in the 1 :100 NaOCl group consumed less chlorine than the previous treatment, p lanktonic bacteria were still recovered at the end of the 28 day study (range: 30 CFU/ml to 5 x 10(6) CFU/ml, median: 130 CFU/ml). A linear regression of all samples (n = 52) using the percentage of active chlo rine recovered versus log CFU/ml yielded an inverse relationship, indi cating that there is an indirect relationship between the amount of ch lorine consumed when treating a dental unit and the number of plankton ic bacteria in the water lines. (C) 1997 Academic Press.