Archaea As Emerging, Fastidious Members of the Human Microbiota

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EDITORIAL 10.1111/j.1469-0691.2012.03904.x

Archaea as emerging, fastidious members of the human microbiota

M. Drancourt Unite´ de Recherche sur les Maladies Infectieuses et Tropicales Emergentes UMR CNRS 6236 IRD 198, FR IDMM, Me´diterrane´e Infection, Aix-Marseille-Uni- versite´, Marseille, France E-mail: [email protected] Article published online: 25 May 2012

It was only approximately 20 years ago that the noun Ar- effective against both bacteria and eukaryotes [9]. Methano- chaea entered the lexicon of clinical microbiology, when it gens, chiefly M. oralis, are also susceptible to topical com- became increasingly apparent that these prokaryotic organ- pounds used as local treatments for periodontopathy. As isms, which form one of the four domains of life, were pres- reviewed by Dridi [3], as well as Mayer and collaborators ent in the human and animal microbiota [1]. Found in harsh [10], non-methanogenic archaeons, including halophilic archa- environments, archaeons were initially tagged as extremo- eons, have been detected by PCR-based methods in the philes, a term that prevented microbiologists from thinking human gut microbiota,. Interestingly, it has been shown that of them in terms of clinical microbiology. The window such organisms could be healthcare-related organisms deliv- opened for the Archaea to be viewed differently when one ered with the purgative administered before colonoscopy organism that forms methane in the mammalian gut, later [11]. This observation indicates that further work is war- named Methanobrevibacter smithii, was found to be an archa- ranted to precisely establish the susceptibility of archaeons, eon [2]. Methane-forming archaeons, named methanogens, including to the biocides that are used for the decontamina- are now recognized as members of the mammal and human tion of colonoscopes. Additionally, the availability of a few gut microbiota; four such methanogens have been cultured, human archaeal genomes (more than 20 M. smithii genomes as reviewed by Be´dis Dridi [3]. In fact, methanogens are fas- are available [12], and the fact that our group has genome- tidious organisms; the isolation and culture of the species sequenced M. luminyensis [4]), should prompt the develop- Methanomassilicoccus luminyensis took more than 1 year [4]. ment of additional molecular methods for the detection and In the review, Be´dis Dridi further states that methanogens genotyping of archaeons in the human microbiota. Genotyp- often escape routine detection, for three main reasons: ing will help to provide an understanding of the sources of microscopic examination is non-specific; the culturing of human archaeons and their dynamics in the microbiota. methanogens requires an unusual atmosphere consisting of Finally, in vitro susceptibility data lead to questioning of the hydrogen; and PCR-based detection requires specific primers effectiveness of current protocols for the decontamination of and probes. Nevertheless, several clinical microbiology teams colonoscopes. Microbiology terminology informs the way in have detected methanogens within the oral, gut and vaginal which microbiologists think about microbes, and clinical mi- microbiota with potential roles in some diseases, including crobiologists should be aware that the word Archaea is inap- obesity, as reviewed by Mayer and collaborators. There is propriate as a name to encompass the wide variety of these now strong evidence implicating the methanogen Methano- organisms, as they have been revealed to be common and brevibacter oralis [5] in periodontopathy. In this situation, not at all archaeal; rather, they now must be regarded as M. oralis has a ‘mafia’ strategy, as its survival is completely emerging and fastidious organisms. dependent on anaerobes, which provide it with hydrogen. Because of this complete dependency on anaerobes, which Transparency Declaration are highly susceptible to metronidazole [6], showing that oral metronidazole suppressed the major gut methanogen M. smithii [7] was somewhat difficult. Here, Saber Khelaifia and I The author has no conflicts of interest to declare. [8] show that, indeed, M. smithii and other methanogens are susceptible to metronidazole and related ornidazole deriva- References tives, which, along with fusidic acid, are the only known effective antibiotics for the treatment of potential methanogen infections. Indeed, methanogens illustrate a paradigm that 1. Boyer M, Madoui MA, Gimenez G, La Scola B, Raoult D. Phylogenetic and phyletic studies of informational genes in genomes highlight exis- the archaeons are susceptible to compounds that are also

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ª2012 The Author Clinical Microbiology and Infection ª2012 European Society of Clinical Microbiology and Infectious Diseases, CMI, 18, 823–824