Effect of triclosan as an antibacterial agent

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Effect of Triclosan as an Antibacterial Agent on Hand Bacterial Flora

Department of Biological Sciences
Vanderbilt University
November, 2009

Triclosan is one of several antimicrobial agents used in commercially-available liquid soaps. The effectiveness of triclosan in reducing bacterial growth on the hands was shown to be significant at high concentrations, but itseffectiveness at lower, commercially-available concentrations and in normal handwashing conditions has been questioned. Using a randomized method, 8 subjects washed one hand with antimicrobial soap and one with nonantimicrobial soap. Finger-stamp cultures of each hand were taken and incubated for 24 hours. The bacterial reduction between pre- and post-wash plates for both the antimicrobial andnonantimicrobial soaps were run in a paired-t test which indicated that the efficacies of each type of soap had no significant difference (prob>|t|=0.8547).

Concerns regarding the efficacy of antimicrobial agents against disease-causing pathogens have led to recent studies into the nature of triclosan, a wide-spectrum antibacterial agent found in consumer “antibacterial” soaps inconcentrations between 0.1% and 0.45% (Aiello et al., 2007). In 5 of 9 recent triclosan studies examined in the Aiello review, researchers reported a statistically significant reduction of bacterial counts on the hands compared to a placebo soap. In many of these studies (Leyden et al., 1991; Bendig, 1990) triclosan was used in high concentrations ≥1.0% Ts or under abnormal handwashing conditions. As of yetthere is insufficient evidence of the effectiveness of triclosan under normal handwashing conditions and in concentrations readily available in consumer antibacterial soaps: only one study (Larson et al., 2003) reported statistically significant reduction in bacterial counts under normal handwashing conditions.
This experiment tested for a significant difference in the percent decrease ofbacterial life (measured in bacterial colony counts) between hands washed with antimicrobial soap and nonantimicrobial soap. Our hypothesis was that there was no significant difference in percent decrease in bacterial growth. Using a randomized finger stamp method, the efficacies of handwashing with antimicrobial and nonantimicrobial soap were compared under normal handwashing conditions.

Materialsand Methods
The first step was to use a graphing calculator program to randomize the order of treatments per subject as well as which hand would be sampled from for each subject. Each subject was assigned a number between 1 and 8 (for labeling purposes). Concerning the order of treatment, the number 0 was assigned to washing hands with the nonantimicrobial soap first and the number 1 wasassigned to washing hands with the antimicrobial soap first. The calculator was programmed to randomly choose one number between 0 and 1 to determine the order. Concerning which hand would be tested for each subject, the number 0 was assigned to the left hand and the number 1 was assigned to the right hand. The calculator was again programmed to randomly choose one number between 0 and 1 to determinewhich hand would be used on the finger stamp. The pointer finger of the assigned hand was assumed to represent the entire hand as a whole. The same hand used for the baseline finger stamp was used for the post-wash finger stamp as well. The agar plates were labeled with each person’s assigned number, the left side was designated as the baseline finger stamp region and the right side of the platewas designated as the post-wash finger stamp region.
At the beginning of lab class, each subject was randomly assigned a hand to be used for the finger stamps. The pointer finger of said hand was slid in a zigzag pattern down the left side of the agar plate assigned to each person, being sure to cover the entire side. Next, each person respectively was given 1 pump of whichever type of soap was...
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