microbiology - How heavy are all foreign microorganisms in and on the human body?

I define "foreign microorganism" as a microorganism which is not produced by the human body (not antibodies or leukocytes) including bacteria, viruses, fungi, biofilm aggregates or small lifeforms independent if they are benign or hostile.

Let's say I have currently a weight of exactly 100 kg. How much of it consists of organisms not belonging to me?

Answer

Edit: Matters Arising

In this Nature News article, Scientists bust myth that our bodies have more bacteria than human cells, and in the bioRxiv pre-print article, Revised estimates for the number of human and bacteria cells in the body, a new estimate of the ratio of microbial cells on the human body to human cells that make up the body has been revised down to close to 1-to-1, with there being slightly more microbial cells to human cells.

It should be noted that near 90% of the human cells taken into account were red blood cells and platelets.

^{- Revised estimates for the number of human and bacteria cells in the body, Sender et.al. bioRxiv preprint.
doi: http://dx.doi.org/10.1101/036103}

Note: Preprint articles have not been refereed. The information in them is subject to change, may not pass review, and in the end my not be accepted for publication.

Readers should therefore be aware that articles on bioRxiv have not been finalized by authors, might contain errors, and report information that has not yet been accepted or endorsed in any way by the scientific or medical community.
^{- bioRxiv.org: What is an unrefereed preprint?}

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Original Post

The human body contains trillions of microorganisms — outnumbering human cells by 10 to 1. Because of their small size, however, microorganisms make up only about 1 to 3 percent of the body's mass (in a 200-pound adult, that’s 2 to 6 pounds of bacteria), but play a vital role in human health.

From: NIH Human Microbiome Project defines normal bacterial makeup of the body

Additional Information on Microbiome and Obesity

From Cell

Altering the Intestinal Microbiota during a Critical Developmental Window Has Lasting Metabolic Consequences

From The American Journal of Gastroenterology Supplements (a Nature Press Journal)

Disclaimer

This article was published as part of a supplement sponsored by the Gi Health Foundation, a nonprofit 501(c)(3) educational organization dedicated to increasing awareness of the effect of gastrointestinal disorders in the United States. The foundation's goal is to provide health professionals with the most current education and information on gastrointestinal health.

Impact of the Gut Microbiota on the Development of Obesity: Current Concepts