Criteria for disease causation
must take microbial
interactions into account
By Allyson L. Byrd1,2 and Julia A. Segre1
In the late 19th century, Robert Koch established his famous postulates as tringent guidelines to evaluate cau- sation in infectious disease (1). These original postulates require isolation of the putative pathogen and reinfection
of a healthy host to prove causation. Over
the years, Koch’s postulates have been continually restated to incorporate the latest
scientific findings and technologies (2–5).
Modern molecular techniques have demonstrated that current or previous members
of a microbial community can affect disease
outcome, providing a nuanced view of strict
causation as originally proposed by Koch.
There is thus a need to incorporate microbial communities into rigorous modern
guidelines for evaluating disease causation.
1 PATHOGEN = 1 DISEASE. Koch’s original
postulates can be summarized as follows:
First, the microorganism occurs in every
case of the disease; second, it is not found
in healthy organisms; and third, after the
microorganism has been isolated from a
diseased organism and propagated in pure
culture, the proposed pathogen can induce
disease anew. Koch did not include the often
1Microbial Genomics Section, Translational and Functional
Genomics Branch, National Human Genome Research
Institute, Bethesda, MD 20892, USA. 2Department of
Bioinformatics, Boston University, Boston, MA 02215, USA.
224 15 JANUARY 2016 • VOL 351 ISSUE 6270
Colored scanning electron
micrograph of Clostridium
difficile bacterial cells
in hospitalized patients.
peptides p. 226 ▶
Graphene tuners for
terahertz lasers p. 229