Bavoil, Patrik

Greub, Gilbert

Kaltenboeck, Bernard

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LETTER TO THE EDITORIn Chlamydia veritasDOI: 10.1111/2049-632X.12026Final version published online 12 February 2013.To the EditorMicrobial taxonomy is an essential tool used to classifystrains into different clades, that is, taxonomic units. Anatural classification system should be based on evolution-ary history, but this is often incompletely known. Hence,taxonomy remains an evolving field changing as newinformation becomes available. While such a classificationsystem is essential for both researchers and clinicians, it isoften poorly adhered to by those who should value it most.Indeed, despite the obvious importance of taxonomy, it isoften considered by clinical and basic researchers as anarbitrary tool of little use or scientific value, and to some, it isjust a painful reminder of years fruitlessly spent learningLatin in high school. Nevertheless, the science we do is onlyas good as the words we use to report it, and taxonomicdenomination and its derivatives lie at the very core of themyriad of scientific words microbiologists use.Take Chlamydia as an example!Chlamydia, known as a sexually transmitted pathogen bysome and as an ocular pathogen by others, is actually apathogen that causes widespread disease in animals andhumans, some of which was first described in antiquity(Trompoukis & Kourkoutas, 2007). Chlamydia provides arich taxonomic history from one of its early scientificdescriptions in 1945 when it was known as Miyagawanella(Jones et al., 1945), and variably later as Chlamydia,Bedsonia or Rakeia (Page, 1966). Fast forward to 1957,and the taxonomic authorities of the time decided on onefamily, the Chlamydiaceae, including two species, Chla-mydia psittaci encompassing all veterinary chlamydialinfections, and Chlamydia trachomatis encompassing ocu-lar and genital infections of humans (Rake, 1957). Thistaxonomy could not withstand the introduction of new,molecular methods, which began to reveal the diversity ofthe Chlamydiaceae, and in 1999, Everett et al. (1999)proposed a new chlamydial taxonomy with two genera,Chlamydia and Chlamydophila, and nine species. Whatfollowed is best described as the era of the ‘Taxon Wars’(www.chlamydiae.com), during which fleets of Chlamydia-philes and Chlamydophiles took over the Chlamydia uni-verse. The former group exceeded the latter and therecommended use of Chlamydophila was poorly adheredto. At the root of the taxonomic dysfunction was a relativelyminor distortion of the taxonomic rules set out in the Everettet al. paper that were not applied to the letter in theproposed classification (Schachter et al., 2001). Others feltthat, as a tool, taxonomy should be practical to its users(Greub, 2010) and that a new genus was simply unneces-sary. More significantly, however, the Everett et al. papersparked a healthy scientific discussion among Chlamydia-philes and Chlamydophiles alike about the unique evolu-tionary path of Chlamydia (and Chlamydophila). Indeed, asdescribed by Stephens et al. (2009) these obligate intracel-lular pathogens have evolved more slowly than their free-living cousins owing to the sequestration and evolutionaryconstancy of their own environment, the cytosolic vacuolebetter known as the chlamydial inclusion. The Everettclassification, however, provided a much-needed practicalclassification at the species level that is now well respectedacross all Chlamydia research disciplines. We refer thereader to the latest rendition of Bergey’s manual (Horn,2011; Kuo & Stephens, 2011), the taxonomic ‘bible’, for adetailed description of the current taxonomy of Chlamydiaand Chlamydia-like organisms, whereby a single genus,Chlamydia, is now used, as well as nine species (abortus,caviae, felis, muridarum, pecorum, pneumoniae, psittaci,suis and trachomatis).We hope this clarifies a confusing situation and concludethis letter by providing a lexicon of commonly usedChlamydia terms.‘Chlamydia’ (italics, always cap C) is the genus(Chlamydophila requiescat in pace) and is most appropriatewhen referring to Chlamydia in general terms.‘Chlamydia’ or ‘chlamydiae’ (plural) (no italics, lower case,cap C only at the start of a sentence) are the latinizedcommon descriptors and should be used equivalent to‘bacterium’ or ‘bacteria’. As a rule, if you can easily replacechlamydia/chlamydiae with bacterium/bacteria in a sen-tence, then that is the way it should be written.‘Chlamydial’ (no italics, lower case, cap C only at the startof a sentence) is the adjective and should be usedequivalent to ‘bacterial’. If you can replace chlamydial withbacterial in a sentence, then you are good.Then, there are the taxonomic groups:‘Chlamydiae’ (always cap C, italics) strictly speaking is thePhylum and hence should be used when referring globally tothe Chlamydiaceae, Parachlamydiaceae and all otherso-called Chlamydia-like organisms not catalogued ordiscovered yet.Below the Phylum, there is the Class ‘Chlamydiia’ (not atypo, two ‘i’s!!!), which no-one ever uses because it onlyincludes one Order, the Chlamydiales, so why bother!Next, ‘Chlamydiales’ is the Order and should be usedwhen referring to more than one Family-level lineage, forinstance the Chlamydiaceae and Parachlamydiaceae.Among the ever-expanding Families are the ‘Chlamydia-ceae’, ‘Parachlamydiaceae’, ‘Waddliaceae’, ‘Simkaniaceae’,‘Rhabdochlamydiaceae’, ‘Criblamydiaceae’, and Candida-Pathogens and Disease (2013), 67, 89–90, © 2013 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved 89Pathogens and Disease ISSN 2049-632Xtus ‘Chlavichlamydiaceae’ and ‘Piscichlamydiaceae’. TheChlamydiaceae are primed for expansion at the specieslevel, and all other families at the genus and species levels,reflecting their greater diversity.In all matters that matter, including taxonomy, there existsa grey area: many will use Chlamydiae to refer to alltaxonomic groups that are below the Phylum level andbecause there is currently only one Class, and one Orderwithin the Class, the Chlamydiales, in essence Chlamydiaeis synonymous to Chlamydiales. However, if you do notwant to confuse readers in about 1 million years from now,when a new Class named Chlamydiiiiiia will surely haveemerged, then you should use Chlamydiales when referringto the Chlamydiaceae, Parachlamydiaceae, Waddliaceae,Simkaniaceae, etc.AcknowledgementsWe thank Drs. Robert Brunham, Gerry Byrne, Lee-AnnCampbell, Gunna Christiansen, Deborah Dean, GraziaGreco, Ted Hackstadt, Johannes Hegemann, MatthiasHorn, Cho-chou Kuo, Simone Magnino, Garry Myers,Andreas Popischil, Roger Rank, Konrad Sachse, PeterTimms, Julius Schachter, Richard Stephens, Ming Tan andPriscilla Wyrick for their support and helpful comments.ReferencesEverett KDE, Bush RM & Aandersen AA (1999) Emended descrip-tion of the order Chlamydiales, proposal of Parachlamydiaceaefam. nov. and Simkaniaceae fam. nov., each containing onemonotypic genus, revised taxonomy of the family Chlamydiaceae,including a new genus and five new species, and standards forthe identification of organisms. Int J Syst Bacteriol 49: 415–440.Greub G (2010) International Committee on Systematics of Prok-aryotes. Subcommittee on the taxonomy of the Chlamydiae:minutes of the inaugural closed meeting, 21 March 2009, LittleRock, AR, USA. Int J Syst Evol Microbiol 60: 2691–2693.Horn M (2011) Phylum XXIV. Chlamydiae Garrity and Holt 2001.Bergey’s Manual of Systematic Bacteriology, 2nd edn (Krieg NR,Staley JT, Brown DR, Hedlund BP, Paster BJ, Ward NL, LudwigW & Whitman WB, eds), p. 843. Springer, New York.Jones H, Rake G & Stearns B (1945) Studies on lymphogranulomavenereum. III. The action of the sulfonamides on the agent oflymphogranuloma venereum. J Infect Dis 76: 55–69.Kuo CC & Stephens R (2011) Family I. Chlamydiaceae. Bergey’sManual of Systematic Bacteriology, 2nd edn (Krieg NR, Staley JT,Brown DR, Hedlund BP, Paster BJ, Ward NL, Ludwig W &Whitman WB, eds), p. 845. Springer, New York.Page LA (1966) Revision of the Family Chlamydiaceae Rake(Rickettsiales): unification of the psittacosis-lymphogranulomavenereum-trachoma group of organisms in the genus ChlamydiaJones, Rake and Stearns, 1945. Int J Syst Bacteriol 16: 223–252.Rake GW (1957) Family II. Chlamydiaceae Rake, Fam. Nov.Bergey’s Manual of Determinative Bacteriology, 7th edn (BreedRS, Murray EGD & Smith NR, eds), p. 957. The Williams &Wilkins Co, Baltimore.Schachter J, Stephens RS, Timms P et al. (2001) Radical changesto chlamydial taxonomy are not necessary just yet. Int J Syst EvolMicrobiol 51: 249.Stephens RS, Myers G, Eppinger M & Bavoil PM (2009) Divergencewithout difference: phylogenetics and taxonomy of Chlamydiaresolved. FEMS Immunol Med Microbiol 55: 115–119.Trompoukis C & Kourkoutas D (2007) Trachoma in the late greekantiquity and the early Byzantine periods. Can J Ophthalmol 42:870–874.Patrik BavoilDepartments of Microbial Pathogenesis &Microbiology and Immunology,University of Maryland,Baltimore, MD, USA,E-mail: pbavoil@umaryland.eduBernard KaltenboeckDepartment of Pathobiology,Auburn University,Auburn, AL, USAGilbert GreubInstitute of Microbiology,Centre Hospitalier Universitaire Vaudoisand University of Lausanne,Lausanne, SwitzerlandPathogens and Disease (2013), 67, 89–90, © 2013 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. 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In Chlamydia veritas

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