Can alcohol kill harmful microbes from our skin?

Dear Editor

Our investigation of the skin microflora after washing hands with the 70% alcohol raised an important concern on the use of hand sanitizers in recent COVID-19 pandemic. Besides that, we have also observed some deadly pathogens commonly found on plants and animals. The human body is one of the largest reservoir of microbial habitats exhibiting a typical biological association with diverse microflora. Usually, biological associations are classified as antagonism or commensalism or mutualism. Human-associated microbial flora is already documented for their association with human health such as - food digestion, pathogen resistance, and educating our immune system (Dethlefsen et al., 2007; Wilson, 2009). Recent studies have further explored gut microflora employing state-of-the-art diagnostic technologies. However, there are limited studies available on skin microflora to understand their impact on human health and forensic implications (Fierer et al., 2010; (Fierer et al., 2008). Human skin microflora, more precisely referred to as the human skin microbiome, refers to the various microorganisms which form the natural habitat of human skin. These unknown residents of human skin are normally thought to be nonpathogenic (Grice and Segre, 2011). The samples were taken in the laboratory before the start of the usual work. For this study a working group consisting of one officer and two research staff engaged in DNA fingerprinting division of State Forensic Science Laboratory, Sagar was randomly recruited for swabbing the skin surface prior to start of work. A pre-sterile swab was used for each individual for taking swabs. A control swab was also taken to remove the possibility of any environmental contamination or observation. The skin swab was taken after 5 min of applying 70% alcohol to the skin surface and rubbing the hands to dry.

Initially, we designed this study with the point of forensic investigation to find the microbial signatures of human skin flora. Interestingly, we observed two major points. First is the observation of harmful bacterial flora isolated through traditional surface sterilization by 70% alcohol. The second observation is the prevalence of microorganisms on the human skin, which have not yet been reported from the skin, though they have been reported as plants (Grice and Segre, 2011; Coenye et al., 2001) and animals pathogens (Musharrafieh et al., 2014).

Previous studies have reported animal-associated microflora, causing disease in human beings (Musharrafieh et al., 2014). We focused on the fingertips and palm bacteria because they mostly come in contact with other surfaces. The skin microbiome has mostly been ignored because hardly 1% of bacterial species can be recovered and identified by culture-dependent assays (Grice et al., 2009; (SWGMAT), 2005; Deedrick and Koch, 2004). Therefore this study has used 16S rRNA based identification of bacterial flora of skin from three individuals (one male and two females) and identified a large assemblage of bacteria, a few significant ones which survived 70% alcohol wash shown in Table S1. Bacteria like Staphylococcus warneri, S. pasture, and other species of Staphylococcus are normal inhabitants of human skin, which were found residing even after 70% alcohol wash as apparent from their growth on normal bacteriological media (Brain Heart Infusion Agar). Moreover, the presence of bacterial genera like Pontibacter indicus, Ornithinimicrobium pekingense, E.coli, Micrococcus luteus, Bacillus pumilus, and Burkholderia sp. raised an alarm as these are potentially pathogenic ones and have survived 70% alcohol wash of the hands. Neighbor-joining tree as well as PCA is presented in Fig. 1 and Fig. 2, respectively, to show the genetic association of these observed microbial signatures with each other from all the three individuals. Though, we did not directly check the effect of 70% alcohol on the SARS-CoV-2. This study becomes more relevant in the present scenario with COVID-19 hazard and blind reliance on hand sanitizers and or alcohol to wash or clean hands for disinfection. The finding raises a serious issue of whether these measures should be relied upon by a common man who believes that using these will completely kill all microbes. The other serious problem is the occurrence of pathogenic bacteria, which can also pose a threat to human life.

Fig. 1.

NJ tree of observed bacterial flora obtained from three individuals.

Fig. 2.

PCA plot of observed bacterial flora obtained from three individuals.

Previous studies have reported animal-associated microflora, causing disease in human beings (Musharrafieh et al., 2014). We focused on the fingertips and palm bacteria because they mostly come in contact with other surfaces. The skin microbiome has mostly been ignored because hardly 1% of bacterial species can be recovered and identified by culture-dependent assays (Grice et al., 2009; (SWGMAT), 2005; Deedrick and Koch, 2004). Therefore this study has used 16S rRNA based identification of bacterial flora of skin from three individuals (one male and two females) and identified a large assemblage of bacteria, a few significant ones which survived 70% alcohol wash shown in Table S1. Bacteria like Staphylococcus warneri, S. pasture, and other species of Staphylococcus are normal inhabitants of human skin, which were found residing even after 70% alcohol wash as apparent from their growth on normal bacteriological media (Brain Heart Infusion Agar). Moreover, the presence of bacterial genera like Pontibacter indicus, Ornithinimicrobium pekingense, E.coli, Micrococcus luteus, Bacillus pumilus, and Burkholderia sp. raised an alarm as these are potentially pathogenic ones and have survived 70% alcohol wash of the hands. Neighbor-joining tree as well as PCA is presented in Fig. 1 and Fig. 2, respectively, to show the genetic association of these observed microbial signatures with each other from all the three individuals. Though, we did not directly check the effect of 70% alcohol on the SARS-CoV-2. This study becomes more relevant in the present scenario with COVID-19 hazard and blind reliance on hand sanitizers and or alcohol to wash or clean hands for disinfection. The finding raises a serious issue of whether these measures should be relied upon by a common man who believes that using these will completely kill all microbes. The other serious problem is the occurrence of pathogenic bacteria, which can also pose a threat to human life.

The need of the hour is to look into this important issue which may lead to a severe health hazard in the society. We suggest thorough investigational research on this topic to frame some concrete guidelines in the public interest.

The following are the supplementary data related to this article.

Table S1

Identified bacterial flora and their known pathogenicity.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.genrep.2021.101207.

Funding

There was no funding body for this study.

Ethics approval

The ethical committee of Jiwaji University, Gwalior approved the study wide letter-number JU/IHEC/2017-A/06 dated 9.3.2017.

Consent to participate

Written informed consent was obtained.

Consent for publication

Written informed consent as per the declaration of Helsinki was obtained from the participants of the study.

Availability of data and material

All the relevant data are given in the manuscript and available on reasonable request from corresponding author.

Code availability

Not applicable.

CRediT authorship contribution statement

PS conceptualized the study, PS and TJ collected the samples and did the processing, VN, and NK helped in the analysis, PS and VN wrote the manuscript, MKG, PKS, RK and GC reviewed the manuscript. PS and VN contributed equally. All the authors read and approve the manuscript.

Declaration of competing interest

Authors declares that they have no competing interests.