These are fungal mycelia. You definitely have fungal contamination in your cell culture room.

Hello Danila Cianciosi

I agree with Julien Dembélé .

Why don’t you perform fumigation in the Tissue Culture Laboratory?

Whenever you wish to perform fumigation ensure that AHU and AC systems are in OFF position. Maintain the temperature of the laboratory at 21-25 degree C and the humidity at 70-80%. Add 25-30 mL of formaldehyde solution (37%) to 10-15g KMNO4 per one cubic meter of space in a glass container that is quite sufficient in size so that the material does not expel out of the container. When mixing with potassium permanganate for fumigation, always add the formalin to potassium permanganate and not the other way. Similarly, use 5g of potassium permanganate and 10-15ml of formaldehyde solution for the airlock. Make use of multiple containers and distribute them throughout the laboratory. Ensure that the entry points are sealed, and the containers may be left overnight in the laboratory.

The next day, you may switch on the AHU system and give an exposure time of at least 4 hours before entering the laboratory. You may neutralize the area by placing ammonia solution in the center of the laboratory and leave it for 3 hours to neutralize the formalin vapor.

Precautions that you may have to take while performing fumigation.

Please wear mask and goggles while performing fumigation. Beware of splashing as the reagents react and the reaction generates heat. Avoid inhalation of the fumes. Also, ensure that the entry doors of the laboratory are sealed after performing fumigation.

At the same time, you may consider sterilizing the CO2 incubator. You may want to refer to the review article attached below. This review gives an overview on the different sterilization procedures for CO2 incubators on the market with emphasize to considerations from a practical point of view. You may go through it as it may be helpful.

https://journals.lww.com/revmedmicrobiol/Abstract/2018/10000/Sterilization_procedures_for_CO2_incubators.1.aspx

Best.

Dear Danila,

In addition to the above answers, I would also recommend monitoring the environmental conditions in your lab areas by using e.g. exposure plates and/or active air sampling, to ascertain the presence of above contaminants and also to assess the effectiveness of the recommenced fumigation.

Also, do you treat the fresh air entering the lab areas in any way (e.g. prefilters, HEPA filters, UV), and do you monitor closely the MiLLiQ system maintenance in relation to filters and UV (as already recommended by Asif Khan) ?