hi

you can use chloromphenicol powder to inhibit bacterial growth.

You can store the spores at low temperature by adding some detergents in a very low concentration. Good to store in a glycerol stocks at -80ºC.

(Stored) spore suspensions are used in a anumber of protocols (see USP -http://www.uspbpep.com/usp31/v31261/usp31nf26s1_c51.asp ).  

Contamination indicates a failure in aseptic technique.  Please focus on improving your technique rather than adding an antibacterial agent.

Thank you Phil.  A suspension should only be spores and nothing more.  The suspension vehicle should be as clean and neat as possible.  Aseptic technique on the front end of preparation is critical. 

For stability of a working inoculum stock suspension the Objectives would be to prevent germination by lowering available water and nutrients.   After harvesting from solid agar, the suspension vehicle (e.g., sterile saline with 0.05% Polysorbate 80) should be used to wash nutrients from the spore suspension.  Centrifugation and decant at least three times.  Visual or spectrophotometer check could verify your end point.  Minimize the final suspension volume to maximize spore concentration in order to remove available water.

For the purposes of a working culture source (for use is assays etc.) I don't think lowering the actual water activity value would be appropriate for this use.  It  would require addition of something like glycerol and again another addition to the working inoculum used in your assay.   

Freeze drying is a whole other question.  Would be interested in recipes. 

Thanks all for your cooperation  this really would help me alot

Hello,

You didn't mention exactly what species of Aspergillus you're working with and what your intended purpose. For example, if you want to immunological studies with spores of a mammalian pathogen and evaluate any kind of response to the fungal spores, those studies carry a much greater risk and negative consequences if ANY bacteria are present. So absolutely improve your ability to isolate your spores and ifyou're experiments are A. nudulans spores in a non-immunological context then without knowing the nature of experiment,, it's hard to be specific. My advice, besides improving your technique with whatever Aspergillus you work with, and if you do expect to do an immunological experiment there's no room for the the presence any significant number of bacteria no matter whether your technique improves, you just can't risk it if your is immunologically relevant. If your experiment is mammalian cells in tissue culture, Penn/Strep is commonly added in the tissue culture medium to prevent bacterial contamination during cell passaging.

Also, if you intend to compare the results of two different strains, then you want to be certain that the viability is similar between the strains. If you do know, you probably to test that and ad.just to CFU/ml not just cells/mL, depending on your experiment. I tend to err on the side of great caution in experiments that involve an immune response to fungal spores where both viability and the presence of bacteria would totally ruin your the experiment or mislead you. I would avoid that situation at all costs. So, for non-immunological assays, I don't mind storing for a bit and the recommendation above are appropriate. If the are immunological and there's a comparison you want to make between two strains and repeating the experiment over again, aside from the need from the need for reproducibility, then I would not let spores of undetermined differences in viability over time, spend much time at 4 degrees. Overnight, depending on how important the viability variable will impact your results. In the case of infection of macrophages with pathogenic spores, I added of penn/strep in my spore samples that were stored overnight for an infection in the morning.

Good luck!

The preparation of spore suspension must be done on the pure culture of fungus after repeated sub cultivation of isolates and addition of recommended antibacterial to the culture medium . On the other hand , before the time of preparation the chamber or  cabinet of work must be sterilized by UV rays  and /or periodical fumigation with pott. perminganate in formalin. All steps during preparation proceeded under sterile condition . Now we have a condition free from any bacterial contamination.

Preparation of spore suspension :

1- Under sterile condition beside a flame , add distilled sterilized water to the pure slant of Aspergillus and scrape gently the upper layer  of mycellial spores and avoid deep scraping to avoid  addition of culture medium to scraped spore.

2- The scraped SPORE  TRANSFERRED to sterilized  bottle

3 - the addition of antibacterial   NOT    recommended after harvesting or  scraping of spore , only added during preliminary cultivation and purification of  culture before preparation of spores

4- A drop of tween 80 could be added to the prepared spore to keep its viability  and kept in fridge at 5-8 degree  till used 

5- Now no any chance for bacterial contamination if all steps done under a septic condition . Otherwise , the contamination if occurred indicated error  in procedures of work and repeating of work is recommended.

Much obligated 

Thanks colleagues for your really helpful answers ,,, but what is wrong with addition of antibacterial ( post harvesting of spores )

I agree with Christoph Ottenheim  and all answers above ...good luck.