I remain convinced that properly formulated antimicrobial soaps have a benefit over bland, non-antimicrobial soaps. You have free article s left. Already a subscriber? Sign in. See Subscription Options. Get smart.
Good 'ol regular soap and water still does the trick.
Sign up for our email newsletter. Of the eligible participants, we enrolled 20 adult males that ranged in age from 18 to 75 years. After obtaining a second informed written consent facilitated by Malagasy translators, ten individuals were randomly assigned to the experimental group to use antibacterial soap for one week, while the other ten individuals were assigned to the control group that would not be administered antibacterial soap.
We selected individuals at random because most participants reported using only local soap, which we observed was used for bathing, washing clothes, and cleaning dishes. We administered Santex antibacterial soap containing Triclocarban, an antimicrobial agent common in Western hygiene products [ 33 ] to the experimental group, as it was difficult to acquire in Mandena and would only be used by the experimental group with explicit instructions to solely use the soap for bathing.
At the conclusion of the study, all subjects were given two bars of Santex soap as compensation for participation. Surveys that inquired about basic health, lifestyle, and demographic characteristics were administered with the help of local Malagasy translators. We sampled each individual at four skin sites right ankle, right medial forearm, right outer hand, right armpit using sterile, dual-tipped rayon swabs Fisher BD BBL CultureSwab, Media-free. All skin swab samples were obtained by rubbing the swab across the site for 30 seconds, with all sampling conducted by authors MBM and JJY.
We provided individuals in the experimental group with both written and verbal instructions to maintain their typical bathing schedule, but to use the soap on specific body parts at each bath time i. We did not provide the control group with instructions regarding soap use because avoiding hygienic practices in this rural environment could put these individuals at risk of disease, and we wished to minimize disruptions to the typical behaviors of our participants. All subjects were swabbed at three different time points to investigate how antibacterial soap use impacts skin microbial composition.
The first sampling event, defined as Time Period 1, took place before the introduction of soap to obtain a baseline skin microbial community sample ; the second, Time Period 2, occurred after one week 7—8 days of antibacterial soap use to investigate the immediate effects of soap use ; and the third, Time Period 3, occurred two weeks 14—15 days after discontinuation of antibacterial soap use to determine any lasting effects of antibacterial soap use Table 1.
We collected the remaining soap at Time Period 2 to ensure discontinuation of antibacterial soap use in the experimental group. At each sampling event, all participants were swabbed once over a span of three days, regardless of whether they received soap. The soap that was administered to the experimental group was weighed at the beginning and end of Time Period 2 to quantify the amount of soap used by each individual. One participant used his entire bar of soap before the sampling event at Time Period 2 and was given a second bar. Because Mandena is not supported by electricity and a laboratory was inaccessible, we stored the samples in a uniformly cool environment in the field and during transit, rather than exposing samples to repeated freeze-thaw cycles.
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A previous study found that differences in short-term storage conditions did not significantly alter microbial communities, and that samples stored in non-freezing conditions were still useful for analyses [ 34 ]. Samples were transported to the United States on three separate flights all within two weeks of collection , using insulated envelopes with ice packs on the plane and hotel room refrigerators when possible during layovers.
To ensure there were no biases between the experimental group and control group, we were first compared the two groups with two separate t-tests, one comparing Shannon diversity index between the two groups and the other comparing observed OTUs between the two groups. We found no significant differences between the two groups for either measure of alpha diversity.
To investigate the impact of antibacterial soap on alpha diversity of skin microbial communities, we compared the change in bacterial taxa for all individuals between Time Period 1 and 2, grouping together individuals that used soap experimental group and individuals that did not use soap control group. We quantified alpha diversity as taxonomic richness number of OTUs , and as combined taxonomic richness and abundance Shannon diversity index. We used paired t-tests with an alpha of 0. We repeated this to compare between Time Period 2 and 3, following discontinuation of soap use.
To investigate if change in alpha diversity covaries with amount of soap used Prediction 2 , we used linear regression models including both the control and experimental group to assess whether the amount of antibacterial soap used had an impact on the number of OTUs or the Shannon diversity index from Time Period 1 to 2. We repeated this process from Time Period 2 to 3 to investigate the relationship between discontinuing soap use and resulting alpha diversity Prediction 3. We defined beta diversity as the UniFrac distance between two of the same samples collected from the same body site on the same individual from different time periods [ 35 ].
A greater UniFrac distance indicates greater dissimilarity between two samples, while a smaller change indicates more similarity. To investigate the impact of antibacterial soap on beta diversity Prediction 4 , we combined all the samples from both the experimental and control group, and then created a general linear regression model to predict the UniFrac distance between two of the same samples from Time Period 1 and Time Period 2, using amount of soap used and age as predictors to determine a dose-response relationship, Prediction 5.
To test whether antibacterial soap use had an impact on microbial composition two weeks after discontinuation of soap Prediction 6 , we generated a general linear mixed model including both the experimental group and control group to predict beta diversity with time period, amount of soap used, and age as fixed effects and participant identity as a random effect. All statistical tests were run in R version 3.
We used linear discriminant analysis effect size LEfSe analysis for the experimental group, separated by time period, to investigate differential abundance of particular microbial taxa affected by soap use [ 37 ]. The amount of soap used significantly predicted beta diversity from Time Period 1 to Time Period 2 Table 2.
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The coefficient indicated a positive dose-response relationship, i. This variable also predicted beta diversity in a general linear mixed model, although sampling period did not Table 3. At all four body sites, with the exception of ankles, soap use was associated with an increase in beta diversity from Time Period 1 to Time Period 2 Fig 1.
LefSe analysis results showed that for the experimental group, differences in microbial communities were at least partially driven by the genera Ramlibacter and Variovorax for Time Period 1 before soap use and Acidovorax for Time Period 2 after one week of soap use Fig 2. We found no significant differences in alpha diversity number of OTUs or Shannon diversity index between samples collected at Time Periods 1 and 2 Table 4.
The control group showed a significant difference in Shannon diversity between Time Periods 2 and 3, while the difference in the number of OTUs approached significance Table 5. In contrast, neither number of OTUs nor Shannon diversity differed significantly between Time Periods 2 and 3 for the experimental group Table 5.
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The amount of soap used or body site was not a significant predictor of change in these metrics across the three time periods. We found that soap use impacts the community composition of microbes on human skin, but may not affect the taxonomic richness of these communities. Changes in community composition persisted for at least two weeks in the experimental group, which suggests that continued use of antibacterial soap may have long-term effects on skin microbial communities.
Similar effects have been documented for the use of other hygienic products, such as antiperspirant and deodorant [ 38 ]. Although we expected that use of antibacterial soap would change the taxonomic richness of skin microbes Prediction 1 , we failed to find any evidence of that relationship, as measured by the number of OTUs and Shannon diversity index across the four body sites Table 4.
Moreover, there was no effect across Time Period 1 to 2 soap use or Time Period 2 to 3 post-soap use Prediction 3. It could be that our small sample size—associated with the challenges of fieldwork in a remote location—limited our ability to detect significant effects. However, the direction of statistically significant results in additional analyses was opposite to that of our predictions, suggesting there was sufficient power in our sample size to detect differences in taxonomic richness.
In addition, each of the 20 participants contributed samples from four different body sites over three time periods, thus vastly increasing our sample size while controlling for the individual sampled. Despite the lack of change in alpha diversity, we found support for predictions related to changes in beta diversity.
There was greater dissimilarity in microbial communities across time in samples from the experimental group than in samples from the control group Table 2 , Prediction 4. This indicates soap use is a driver of variation in microbial community composition. In addition, the magnitude of the coefficients in our models covaried with the amount of soap used Table 2 , indicating a dose-response relationship Table 2 , Prediction 5. Interestingly, soap use covaried with greater beta diversity i. This may be due to increased contact between ankles and the outside environment, compared to other body sites.
This is in line with findings from a similar study in Mandena, where ankle samples exhibited greater similarity to domesticated cattle than did other body sites, likely due to shared environment of unshod human feet and cattle while working in the agricultural fields [ 8 ]. In this light, perhaps soap use affected microbial communities on body sites that contained typical human skin microbes, whereas ankles contained more environmentally-sourced microbes that were less affected by soap use.
Our LefSe analysis Fig 2 indicated that the differences in microbial communities over the three time periods were driven by the genera Ramlibacter , Variovorax , and Acidovorax , all of which are part of the family Comamonadaceae , which consists of environmental bacteria from water and soil, as well as certain pathogens [ 39 ]. It may be that soap use reduced certain bacterial taxa, allowing other formerly unsuccessful taxa to colonize the open niches. Previous research demonstrated that bacteria compete for limited resources, and that when certain bacterial strains die, other species can successfully colonize the area [ 15 , 19 ].
While this would present a community-level shift in composition, it may result in minimal changes in overall species richness i. This could also explain our finding that soap use does not predict change in alpha diversity, but does have an effect on beta diversity. In this rural setting, individuals come into close contact with multiple, diverse sources of environmental bacteria [ 8 ]. This could result in two, non-mutually exclusive phenomena: i after soap use, open niches on the skin could quickly be filled by environmentally-derived taxa that normally are unable to compete with the resident skin microorganisms; and ii irrespective of soap use, human skin microbial communities harbor taxa that are typically considered to be environmentally sourced.
The latter could explain the unexpected finding that Shannon diversity index significantly increased in samples from the control group Table 5. In addition, it may be that the introduction of soap prompted the experimental group to bathe more frequently than is typical in this setting and perhaps more frequently than the control group , due to an induced pressure to use the soap and present clean skin at sample collection events.
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The common practice of bathing outdoors in the communal river could lead to increased exposure to water and soil taxa, therefore counteracting effects of soap use on skin microbial communities that are observed in Western settings. Importantly, time period was not a significant predictor of beta diversity based on our general linear mixed model Table 3 , indicating that shifts in microbial communities persisted for at least two weeks Prediction 6. This is relevant for considering potential long-term health impacts of antibacterial soap.
Further studies could investigate the duration of the effects of soap, and whether they can induce a permanent change in microbial community composition. This effect on microbial communities may also be an avenue for the emergence of antimicrobial resistance; as such, future studies should target bacterial taxa that are most likely to acquire resistance.
In , the FDA urged continued research on the possible effects of antibacterial soap use, especially soaps containing the active ingredients Triclosan and Triclocarban. Three years later, the FDA prohibited the sale of hygiene products containing these antibacterial agents [ 26 ]. As the soap used in our study contained Triclocarban, these results are relevant to concerns raised by governmental organizations and citizen advisory groups, and future studies should continue to investigate the effects of these products on health.
While evidence suggests that soap use is more effective at reducing bacterial contamination than is washing with only water [ 23 ], recent studies indicate that washing with antibacterial soap is no more effective at reducing bacterial levels than is the use of regular soap [ 42 — 45 ].
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Similarly, antibacterial soap is no more effective at reducing disease incidence on a community level than is non-antibacterial soap [ 24 ]. Antibacterial cleaning agents have fast become a popular alternative to traditional cleaning products. These soaps, shampoos, dishwashing detergents, and toothpastes …show more content….
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