Editorial The Acetobacteraceae: Extending the Spectrum of Human Pathogens David Fredricks, Lalita Ramakrishnan

atients with chronic proposed, Koch’s postulates, so named disseminated disease in patients with granulomatous disease (CGD) by the students of Robert Koch, remain neutropenia, but it is also a common P get recurrent infections with a the gold standard for proving that a colonizer of the gastrointestinal tract variety of bacterial and fungal microbe is the cause of a disease. In one of immunocompetent humans in whom pathogens as a consequence of of the most influential papers in the it does not produce disease. Further phagocyte defects in production of history of microbiology, ‘‘Die complicating matters, not every antimicrobial reactive oxygen Aetiologie der Tuberkulose’’ (‘‘The episode of neutropenic fever is caused metabolites. Patients with CGD often Etiology of Tuberculosis’’), presented by C. albicans, as other fungi, bacteria, present with clinical syndromes, such as before the Physiological Society of and viruses are also pathogens in this pneumonia or lymphadenitis, for which Berlin in 1882, Koch tried to convince setting. Koch’s postulates were no credible pathogen is identified, his colleagues that a novel bacterium, conceptualized at a time when our leading to empirical broad-spectrum Mycobacterium tuberculosis, was the cause attention was focused on clinical antibacterial and antifungal therapy. of tuberculosis [2]. syndromes such as anthrax and The question beleaguering the clinician The elements of Koch’s postulates pulmonary tuberculosis, which were so in this scenario is whether the patient is are summarized in Box 1, and it is clear distinct that they were easily infected with a common microbe (e.g., that the authors have left no stone recognizable even by the laity. Many Aspergillus fumigatus, Nocardia asteroides, unturned to fulfill these postulates to infectious syndromes in today’s Staphylococcus aureus) that has eluded provide a causal link between their practice are without hallmark detection, or a novel fastidious new, isolated organism and the CGD symptoms and signs. Not surprisingly, microbe. episode in this patient. In considering then, the authors’ attempt to address In this issue of PLoS Pathogens, David them one by one, it is important to elements 1 and 2 by examining the Greenberg, Steven Holland, and note that elements 1 and 2 were reactivity of serum from patients with colleagues [1] have isolated and problematic even in Koch’s time: he CGD and from controls to the new characterized a new bacterium, noted difficulties in fitting all microbe– bacterium led to ambiguous results: Granulobacter bethesdensis, from the disease associations to his causal three of 19 patients with CGD versus lymph nodes of a patient with CGD and paradigm—for instance, in the case of one of 20 controls were positive. These recurrent idiopathic lymphadenitis. Vibrio cholerae, wherein some subjects results are difficult to interpret given They have shown that G. bethesdensis were found to be colonized with the that we do not know if the organism is represents a new genus and species in bacterium without having the an occasional transient human the Acetobacteraceae family. The characteristic cholera disease [3]. commensal, and do not know how long bacterium was repeatedly isolated in Advances in microbiology since the immunoreactivity is maintained after charcoal–yeast extract medium from 19th century have demonstrated the exposure. Encouragingly, the authors several lymph nodes of the patient over important contributions of the host several months. The patient’s serum (immunity), vector, and environment to from prior to the current episode had disease susceptibility and response, and Citation: Fredricks D, Ramakrishnan L (2006) The been banked, allowing them to these elements are not considered in acetobacteraceae: Extending the spectrum of human demonstrate seroconversion by whole Koch’s original postulates. Indeed, even pathogens. PLoS Pathog 2(4): e36. DOI: 10.1371/ journal.ppat.0020036 lysate immunoblot and in the case of tuberculosis, many immunoelectron microscopy. asymptomatic individuals harbor M. DOI: 10.1371/journal.ppat.0020036 Furthermore, the patient’s G. tuberculosis for prolonged periods Copyright: Ó 2006 Fredricks and Ramakrishnan. This bethesdensis isolate produced a similar without suffering from the disease. In is an open-access article distributed under the terms of the Creative Commons Attribution License, which pyogranulomatous lymphadenitis in recent decades, elements 1 and 2 have permits unrestricted use, distribution, and mouse models of CGD but not in become ever more complex as the reproduction in any medium, provided the original control mice. Finally, the 16S rRNA distinction between commensal and author and source are credited. gene sequence of the bacterium pathogen has further blurred as a result Abbreviation: CGD, chronic granulomatous disease reisolated from infected mouse tissues of modern medical advances such as David Fredricks is at the Fred Hutchinson Cancer was identical to the sequence from the cytotoxic cancer therapies and Research Center, Seattle, Washington, United States of America, and in the Department of Medicine, bacterium originally isolated from the immunosuppression related to University of Washington, Seattle, Washington, patient. Do these data prove that G. transplantation. Increasingly, one United States of America. E-mail: [email protected]. bethesdensis is a cause of lymphadenitis person’s commensal may be another Lalita Ramakrishnan is in the Departments of Microbiology, Immunology, and Medicine, University in patients with CGD? person’s pathogen. For instance, of Washington, Seattle, Washington, United States of Some 124 years after they were Candida albicans can produce America. Email: [email protected].

PLoS Pathogens | www.plospathogens.org0249 April 2006 | Volume 2 | Issue 4 | e36 and nucleic acid sequence information source used by these bacteria in vivo? Box 1. Koch’s Guidelines for (Fredricks and Relman) [4]. Greenberg From the point of view of treatment, it Determining if Etiologic Microbes at al. have used immunological and is disturbing to note the high-level Are the Cause of Disease sequence evidence to nicely bolster resistance of the bacteria to virtually all their case for causation. classes of antibiotics and treatment 1. Should be found in every case of the disease 2. Should not be found in individuals without Bacteria in the Acetobacteraceae failure with the two antibiotics disease family are not common human (doxycycline and trimethoprim- 3. Should be isolated in pure culture on lifeless pathogens, but are commonly found in sulfamethoxazole) to which the media and be capable of causing the soil and associated with plants. The bacteria were transiently susceptible characteristic disease anew upon inoculation acetobacteraceae are known to convert upon isolation. This result highlights in a susceptible host ethanol to acetic acid and are the grim problem of antibiotic 4. Should be reisolated from the susceptible responsible for the conversion of wine resistance, either intrinsic to the host to vinegar. Asaia bogorensis is the only bacterium or induced by antibiotic other bacterium in this family that has therapy. The authors propose to obtain report the recent isolation of been associated with human disease a whole genome sequence of the molecularly distinct isolates of G. and isolated from the peritoneal fluid bacterium, which may begin to answer bethesdensis from two other patients of a patient undergoing peritoneal some of these questions. “ with CGD presenting with a similar dialysis [6]. Both A. bogorensis and G. bethesdensis were identified by syndrome. Acknowledgments The authors have done an sequencing their 16S rRNA genes and outstanding job addressing elements 3 performing phylogenetic analysis. The Funding. The authors received no specific and 4. In this regard, they were increasing use of sequence-based funding for this article. tenacious in pursuing different growth methods for the identification of Competing interests. The authors have declared that no competing interests exist. media and were fortunate that one of microbial pathogens in the clinical them was hospitable for the pathogen’s microbiology laboratory is likely to References growth. However, the application of greatly expand our understanding of 1. Greenberg DE, Ding L, Zelazny AM, Stock F, these elements of Koch’s postulates can the diversity of microbes pathogenic Wong A, et al. (2006) A novel bacterium associated with lymphadenitis in a patient with also present practical problems. For for humans. It will serve the chronic granulomatous disease. PLoS Pathog instance, not every pathogen is capable microbiological community well if the 2: DOI: 10.1371/journal.ppat.0020028 of propagation in the laboratory on discoverers of these novel microbes 2. Koch R (1882) Die aetiologie der tuberkulose. Berliner Klinische Wochenschrift 19: 221–230. lifeless (cell-free) medium, and some of apply the same rigor toward 3. Evans AS (1993) Causation and disease. New these pathogens include Mycobacterium establishing causality that was York: Plenum Medical Book Company. 238 p. leprae, Treponema pallidum, and all demonstrated by Greenberg at al. 4. Fredricks DN, Relman DA (1996) Sequence- based identification of microbial pathogens: A viruses. Thus, modifications have been Finally, the data presented in the reconsideration of Koch’s postulates. Clin proposed to make Koch’s postulates paper raise intriguing questions about Microbiol Rev 9: 18–33. more comprehensive by allowing their pathogenesis and treatment. From 5. Falkow S (1988) Molecular Koch’s postulates applied to microbial pathogenicity. Rev Infect application to viruses (Thomas Rivers) which niche did the bacterium infect Dis 10: S274–S276. and by incorporating immunological these patients? Is infection associated 6. Snyder RW, Ruhe J, Kobrin S, et al. (2004) criteria (Alfred Evans), epidemiological with the consumption of certain fruits Asaia bogorensis peritonitis identified by 16S ribosomal RNA sequence analysis in a patient criteria (Austin Bradford Hill), or vegetables? How did the bacteria get receiving peritoneal dialysis. Am J Kidney Dis pathogenicity (Stanley Falkow) [4,5], to the lymph nodes? What is the carbon 44: e15–e17.

PLoS Pathogens | www.plospathogens.org0250 April 2006 | Volume 2 | Issue 4 | e36