"Of the trillions of cells in a typical human body only about one in ten is human. The rest are microbial."
New York Times Magazine 13th August 1996
And then there is this longer extract from a description of human flora in Wikipedia:
We talk of reproducing in order to ensure the survival of our genes, but microbes that existed millions of years before 'higher' life forms which they inhabit. Are we just a creation by mutation for the benefit of the microbes that make up 90% of the cells in our bodies?Populations of microbes (such as bacteria and yeasts) inhabit the skin and mucosa. Their role forms part of normal, healthy human physiology, however if microbe numbers grow beyond their typical ranges (often due to a compromised immune system) or if microbes populate atypical areas of the body (such as through poor hygiene or injury), disease can result.
Traditionally, bacteria have been described by how they grow - what they grow on, color of the colony, and so forth. More recently, bacteria have been described on the basis of DNA sequencing. One common finding is that the number of bacteria - both in terms of diversity (number of different types) and in terms of mass (total number of cells) - is very different when a surface is sampled for culturable bacteria or sampled for DNA. DNA evidence suggests that well-described species - in essence, species that can be cultured - constitute <10% of the total bacterial population seen with DNA-based techniques; that is, most of the bacteria present on the human skin or in the gut are species known only by their DNA, and are species that until very recently were completely unknown to science.
It is estimated that 500 to 1000 species of bacteria live in the human gut and a roughly similar number on the skin. Bacterial cells are much smaller than human cells, and there are at least ten times as many bacteria as human cells in the body (approximately 1014 versus 1013). Though members of the flora are found on all surfaces exposed to the environment (on the skin and eyes, in the mouth, nose, small intestine), the vast majority of bacteria live in the large intestine.
Many of the bacteria in the digestive tract, collectively referred to as the gut flora, are able to break down certain nutrients such as carbohydrates that humans otherwise could not digest. The majority of these commensal bacteria are anaerobes, meaning they survive in an environment with no oxygen. Normal flora bacteria can act as opportunistic pathogens at times of lowered immunity.
Escherichia coli (a.k.a. E. coli) is a bacterium that lives in the colon; it is an extensively studied model organism and probably the best-understood bacterium of all. Certain mutated strains of these gut bacteria do cause disease; an example is E. coli O157:H7.
A number of types of bacteria, such as Actinomyces viscosus and A. naeslundii, live in the mouth, where they are part of a sticky substance called plaque. If this is not removed by brushing, it hardens into calculus (also called tartar). The same bacteria also secrete acids that dissolve tooth enamel, causing tooth decay.
Hmmm... Turns a lot of ideas on their heads, and is not I believe foreseen or acknowledged in the Holy books of Christianity or Islam.