New sequencing data from researchers in Japan has highlighted that even tightly regulated cleanrooms harbour unseen microbial communities.
The study puts forward evidence that significant numbers of airborne bacterial communities are missed by conventional particle counts or culture-based methods.
The team states in the paper that microbial diversity and community structures could not be fully captured by these more traditional methods.
To discover this, the team applied 16S rRNA gene-based metagenomic analysis.
“This study demonstrates the limitations of conventional culture-based monitoring and underscores the value of DNA-based approaches for characterising airborne microbial communities in cleanrooms,” writes Mitsuru Mizuno, Assistant Professor at Institute of Science Tokyo, who worked on the study.
Mizuno’s team, in collaboration with researchers at the Institute of Science Tokyo, biotechnology startup bitBiome (Waseda University), and Takenaka Corporation, collected airborne bacterial DNA from Grade B, C, and D cleanrooms.
Across all cleanroom grades, the team consistently detected skin-associated microbes such as Cutibacterium and Corynebacterium, and environmental bacteria Bacillus and Paracoccus.
Skin-related microbes are inevitable from human workers, but the study findings indicate that these microbes are present only occasionally and temporarily and do not establish a permanent or widespread source of contamination.
The study underscores a limitation of traditional monitoring: many airborne microbes cannot be cultured or do not grow under standard lab conditions.
The researchers found that the cleanroom grade did not make a difference when it came to microbial diversity.
The study gives evidence that microbial diversity was instead shaped by localised airflow, human movement, work tasks, and equipment usage.
The observations echo conclusions published earlier this year by NASA: in low-mass environments, contamination is unavoidable when operating near the limits of detection.
Future technologies for contamination prevention
Humans remain an unavoidable source of cleanroom contamination, and as a result Mizuno and his team determined that complete prevention is impossible.
This means that there will always be some level of microbial presence and there will always be some minimal or manageable low-level microbial risk.
Mizuno’s team argues that future technological efforts must focus on the creation of fast-acting detection systems to identify and mitigate contaminants before they affect quality or patient safety.
In this way, any future strategy used to keep cleanrooms clean cannot be a complete war on germs, but to figure out how to live safely with harmless microbes and use technology to eliminate the dangerous ones.
Mitigating contamination with airflow
In a follow-up study also published in Regenerative Therapy, Mizuno’s group and Takenaka evaluated air-barrier cleanrooms designed for cell-processing operations.
The team replaced doors with unidirectional air curtains and the move significantly reduced the transfer of particles, down to 0.013% in physical tests and an estimated 0.004% in simulations.
Among the airflow designs tested, the push-pull ventilation delivered the best containment during operator transitions.
While testing the supply-air flow with 500mm wing walls provided moderate protection.
The team found that door-free architectures tested could facilitate robotic integration into the cleanroom workflow, but that airflow engineering alone cannot eliminate contamination.