Beware! Scores of micro-organisms lurk unseen in dark and dusty corners of your home and office, including some that are found in the human gut.

Now Finnish scientists are edging closer to cataloguing exactly what might be sharing space with you in your indoor environment.

As part of the study, indoor dust samples were taken from two similar buildings located 100 km apart, but similar in age, ventilation, use and location.

Offices in the two buildings were sampled at different times during one year to obtain four samples per building, one for each season.

By examining dust samples lifted with the help of a vacuum cleaner, lead researcher Helena Rintala found that the dust was dominated by what is called gram-positive bacteria.

This group includes staphylococcus and streptococcus species that belong to the normal bacteria in humans. Approximately 500 species were estimated to be present in the dust.

The findings of the study have been published in the latest issue of the journal BMC Microbiology.

"People spend most of their lives in different indoor environments: homes, schools, workplaces," explained Rintala. "And as such we are constantly challenged by airborne microbes.

"It is important then to understand the exact nature of this exposure and to be able to understand how it affects our health."