The International Space Station is teeming with bacteria and fungi that can cause diseases, a new study found.

They also form biofilms that can promote antibiotic resistance and even stop spacecraft parts from working correctly, scientists warn.

The findings are important to protect the health of astronauts and the safety of crafts on future manned long missions to Mars and beyond.

The International Space Station (pictured) is teeming with bacteria and fungi that can cause diseases, a new study found. They also form biofilms that promote antibiotic resistance and can even corrode the spacecraft, scientists warn

The station - built in 1998 and orbiting around 250 miles (400 km) above the Earth - has been visited by over 222 astronauts and up to six resupply missions a year up until August 2017.

The station's components were built in sterile environments before being sent into orbit and routine monitoring has taken place since.

However, a comprehensive catalogue of what is lurking on inside surfaces has until now been absent.

NASA scientists found that the microbes on the ISS mostly came from people and were similar to those found in public buildings and offices here on Earth.

The most prominent bacteria were Staphylococcus - making up over a quarter (26 per cent) of total species isolated from samples taken - followed by Pantoea (23 per cent) and Bacillus (11 per cent).

They included organisms that are considered opportunistic pathogens on Earth.

That includes Staphylococcus aureus, which made up a tenth of total isolates identified. It is commonly found on the skin and in the nasal passage.

Experts also located Enterobacter, which is associated with the human gastrointestinal tract.

'The International Space Station is the largest human space platform in low Earth orbit - around 400 km above Earth's surface - and for the last 17 years it has been continuously inhabited by an international community of astronauts performing space research,' said paper author and microbiologist Kasthuri Venkateswaran of NASA's Jet Propulsion Laboratory in California.

'The ISS is a hermetically sealed closed system, subjected to microgravity, radiation, elevated carbon dioxide, and the recirculation of air through HEPA filters and is considered an "extreme environment."

'Microbes are known to survive and even thrive in extreme environments, and the microbes that are present on the ISS may have existed since the inception of the ISS while others may be introduced each time new astronauts or payloads arrive.'

He added that emerging studies of the 'built microbiome' here on Earth show that the design of offices, classrooms, museums and hospitals influence the assemblages of bacteria, fungi, viruses, and protozoa that end up being unique to each indoor environment.

'Specific microbes in these indoor spaces have been shown to impact human health by influencing our susceptibility to allergies, infectious diseases, or sick building syndrome,' he added.

'The influence of the indoor microbiome on human health becomes more important for astronauts during flights due to altered immunity associated with space flight and the lack of sophisticated medical interventions that are available on Earth.

'In light of an upcoming new era of human expansion in the universe, such as future space travel to Mars, the microbiome of the closed space environment needs to be examined thoroughly to identify the types of microorganisms that can accumulate in this unique environment, how long they persist and survive, and their impact on human health and spacecraft infrastructure.'

Microbes identified on the station included organisms that are considered opportunistic pathogens on Earth, such as Staphylococcus aureus (pictured, stock image), which is commonly found on the skin and nasal passages making up a tenth of total isolates identified

Monitoring bugs in space used traditional culture methods, although it is known that many microbes cannot be cultured with standard techniques.

To fully appreciate the true number and diversity of microbes that survive in the ISS, researchers used traditional culture techniques and gene sequencing methods to analyse surface samples.

The researchers collected surface bacteria and fungi samples from eight locations within the ISS - including from a dining table, exercise platform, sleeping quarters, toilet and a viewing window.

Swabs were taken repeatedly from each site during three different missions across a total period of 14 months, to see how the fungal and microbial populations changed over time as well as between different locations.

The experts found that while fungal communities on the space station remained largely stable, the microbe populations were similar across the ISS but changed as time progressed.

For example, the microbe samples swabbed during the second mission had a higher population diversity than those collected during the other two periods.

The experts believe that these changes may be a result of the different astronauts living on the ISS during each mission.

They found the ISS swabs were similar to other built environments where the microbiome is shaped by human occupation.

'Whether these opportunistic bacteria could cause disease in astronauts on the ISS is unknown,' said paper author and microbiologist Aleksandra Checinska Sielaf, of the Washington State University.

'This would depend on a number of factors, including the health status of each individual and how these organisms function while in the space environment.

'Regardless, the detection of possible disease-causing organisms highlights the importance of further studies to examine how these ISS microbes function in space.'

And many of the organisms detected on the ISS are known to form biofilms that belong to both bacterial (Acinetobacter, Sphingomonas, Bacillus, Burkholderia, Corynebacterium, and Klebsiella) and fungal (Penicillium, Aspergillus, Cryptococcus, and Rhodotorula) genera.

This could pose problems for astronauts if they become infected as biofilms are known to promote resistance to antibiotics while biofilm formation 'could decrease infrastructure stability by causing mechanical blockages, reducing heat transfer efficiency, and inducing microbial influenced corrosion.'

'Some of the microorganisms we identified on the ISS have also been implicated in microbial induced corrosion on Earth,' said paper author Camilla Urbaniak, a microbiologist at the Jet Propulsion Laboratory.

'However, the role they play in corrosion aboard the ISS remains to be determined.'

'In addition to understanding the possible impact of microbial and fungal organisms on astronaut health, understanding their potential impact on spacecraft will be important to maintain structural stability of the crew vehicle during long term space missions when routine indoor maintenance cannot be as easily performed.'

'Our study provides the first comprehensive catalogue of the bacteria and fungi found on surfaces in closed space systems and can be used to help improve safety measures that meet NASA requirements for deep space human habitation,' Dr Venkateswaran concluded.

'The results can also have significant impact on our understanding of other confined built environments on the Earth such as clean rooms used in the pharmaceutical and medical industries.'

The full findings of the study were published in the journal Microbiome.