Recipe for DG-18 Agar

Fungal growth on DG-18 Agar

The primary organisms on these two DG-18 agar plates include Penicillium spp., Cladosporium spp., Aspergillus spp., and Wallemia spp. 

Our lab uses DG-18 or Dichloran Glycrol agar to grow culturable xerophilic (dry loving) fungi on indoor air and surface samples. This DG-18 agar grows mould or yeast at water activity (aw) less than .85).  The restricted colony growth and the inhibition of the zygomycete fungi on the plate allow for easier identification and counting of mould colonies on the plate. Some water loving moulds like Stachybotrys spp. and Aspergillus fumigatus do not grow well on this media. We often pair plates of MEA (Malt Extract Agar) with the DG-18 agar to capture organisms needing higher water activity.

DG-18 Media Recipe:

• 172 milliliters (ml) of glycerine
• 31.5 grams (g) of DG-18 dry powder agar
• 1000 ml of distilled water
• 0.1 g of chloramphenicol in 5 ml of 70% ethanol suspension (add after other ingredients are mixed) - This antibiotic limits bacterial growth on the culture plate.  Autoclave the culture plates after identification to limit problems with the development of antibiotic resistance. 

Directions:

1. Heat mixture to boiling using stir bar and a hot plate in a covered 2 liter flask. Make sure all media dissolves into solution.  Observe and modify the stir plate temperature to prevent it from boiling over. 
2. Use insulated gloves to transfer liquid agar solution to an autoclave.
3. Autoclave  for a 60 minute cycle at 121 C. 
4. Remove and keep warm in a 60 C incubator. 
5. Pour out 13.5 ml of agar onto a Rodac plate or 25 ml onto a 100 petri dish on a laminar flow clean bench.  Refrigerate covered in a plastic bag and store for up to 3 months. 

Acrodontium spp.

Acrodontiium spp. on DG-18

The organism, Acrodontium spp. was found to be a laboratory contaminant on culture plates.  The organism is similar to several other organisms.  The colony growth is slow on DG-18 agar with white fluffy restricted growth at 5 days.

Acrodontium spp. 400x (25 microns between 6 and 7)

The lower end of the conidiophore is wider at the base then the conidia producing structure at the tip of the conidiophore.  I identified the organism using the key in the book, The Genera of Hyphomycetes.   These spores would not be identifiable to genera on an Air-o-cell cassette sample.

Illustrated Genera of Imperfect Fungi by Horace Leslie Barnett

As a student, I used an earlier edition of this book for identifying fungi in my mycology class at the University of Minnesota.  The addition of photos in the front of the book are a welcome improvement over the original text.  Multiple similar organisms are pictured on the same page and this helps to differentiate between them for identification.

Link to book: Illustrated Genera of Imperfect Fungi 4th (fourth) Edition by Barnett, Horace Leslie, Hunter, Barry B. published by Amer Phytopathological Society (1998)

The book is useful for both the beginning mycologist focusing on indoor air and the plant pathologist.  The line drawings aide in identification.  The addition of a 10 micron scale to each of the drawings would also make it even more useful. 

This book provides an excellent companion to Identifying Filamentous Fungi and The Genera of Hyphomycetes. 

Hyaline monomorphic fungi Glen Roberts PhD part 4 - 20 min.

Hyaline monomorphic fungi Glen Roberts PhD part 5 - 29 min.

Hyaline monomorphic fungi Glen Roberts PhD part 6 - 13 min.

Identifying Fungi by Guy St. Germain and Richard Summerbell

I have used the lab reference book Identifying Fungi 2nd Edition by Guy St-Germain and Richard Summerbell as the text for a course on indoor air fungal identification taught at the University of Minnesota.  The students like the accessible format with both a textual and visual key at the beginning of the book.  Each organism has a line drawing to scale, a photo of the organism in culture and a photo of the organism under light microscopy. 

The glossary and suggestions media and stains are also helpful.  I have met both of the authors.  Guy St-Germain took a class with me in San Antonio, Texas with the National Laboratory Training Network.  Richard Summerbell taught a section of a fungal identification course in Ottawa, Canada. 

As we've trained staff in our department on fungal identification, this book and the first edition have been the one we've used to get them started to become competent at identifying some of the most common indoor molds on culture. 

Identifying filamentous fungi Glen Roberts - PhD - part one - 24 min. 

Monomorphic fungi Glen Roberts - PhD - part two - 26 min.

Monomorphic fungi Glen Roberts - PhD - part three - 16 min.

The Genera of Hyphomycetes by Keith Seifert and others

The Genera of Hyphomycetes

I recently borrowed a copy of The Genera of Hyphomycetes in the McGrath Library of the St. Paul Campus of the University of Minnesota. This massive tomb of nearly 1,000 pages took over twenty years to complete. There are close to 1,000 line drawings of hyphomycetes classified by spore type.  I ended up using the book to help identify a fungal organism growing on a window ledge.

I had the opportunity to meet the principal author, Keith Seifert, where he was one of several lecturers at a fungal identification workshop in Ottawa, Canada many years ago. At that time his specialty was the genus Fusarium spp. The class was excellent, as was the city and the dining.  During the conference we were able to attend a traveling Renoir portrait exhibit at the local museum. Each painting included historical information about the subject(s).  Of all the paintings in the exhibit, I found the large portrait of Monet painting in his garden to be the most intriguing.

The plants in our gardens survive because mycologists working as plant pathologists quietly do work that reveals the complex often multi-host ecology of these fungal organisms. Medical mycologist work on human disease prevention. In health and safety, we poke around the edges of mycology trying to our best to keep people alive, buildings from rotting, and research on other organisms free from contamination. I very much appreciate the work these authors put into this book to help all of us who search around the edges.

Gentle teasing of the Author Keith Seifert by P. W. Crous and R. A. Samson 2 min.

Importance of Hyphomycete taxonomy - Keith Seifert 17 minutes.

Identifying moldy fruit in the refrigerator

Moldy black raspberry

Keeping fruit fresh in a refrigerator is a challenge.  These black raspberries became moldy after less than a week in a refrigerator.  Most of the mold on the surface was mycelia without reproductive structures.  I used a clear 3M transparent tease tape and with a 85% lactic acid mixed with fuchsin dye to identify the organism under 400x power.

Low resolution photomicrograph of Botrytis spp.  - N. Carlson

Close up of Botrytis spp. growing on the black raspberries - N. Carlson 

Photomicrograph of Cladosopoium spp. growing on the black raspberries. - N. Carlson

Identifying moldy vegetables in the refrigerator

Moldy red pepper - N. Carlson

With a microscope at home it's fun  to check on what's growing items that have gone way beyond the best by date.  These red peppers were in a closed container for more than a couple weeks.  The primary organisms identified were yeast and the dark colored Cladosporium spp. The Fridge temperature was reading 36 degrees F. or a 2.2 degrees C.

Yeast - N. Carlson

Cladosporium spp. - N. Carlson

IAQ radio interview with Andrew Streifel U of MN

Andrew Streifel - N. Carlson

I've had the pleasure to work with Andrew Streifel for over 30 years, first as a graduate student and then as a co-worker at the University of Minnesota Department of Environmental Health and Safety.  He is a prolific author of journal articles, an excellent speaker and the go to consultant for hospitals around the world when they are trying to solve a difficult infection control problem.

In the summer of 2017, he was interviewed on IAQ Radio discussing aspects of health care acquired infections, formerly known as nosocomial or hospital acquired infections.  In IAQ Radio Episode 470 Andrew Streifel, he reviewed the major areas of concern including infection sources, sampling methods and case studies of patient infections.

This is a list of just some of the factors mentioned that contribute to health care acquired infections:

• The clothing worn by guests visiting a patient can be contaminated with spores from the outdoor air.
• The previous occupant of a patient care room may pass their infection onto the next patient. Therefore, the quality of surface decontamination between patients is critical. 
• Improper installation of building filters allows outside air to by pass the filters. 
• A negatively pressurized building can bring in unfiltered air into the patient care area. 

I hope you get a chance to listen to the full interview. It provides many helpful suggestions for investigating health care acquired infections.

Andrew Streifel on IAQ Radio - 1 hour

Flir-one pro IR camera

Photo of a slot supply diffuser with two small water leaks in blue on the lower right - N. Carlson

I have been pleased with the original FLIR ONE IR cell phone camera attachment and decided to upgrade to the FLIR ONE PRO as the resolution was increased by a factor of four and the upper end of the temperature range increased to 400C.  

Notes: The Android phone adapter is a C connection which has a benefit in that the camera can be orientated front or back.  The attachment will require an adapter for older phones like the Samsung J7 or the S5. The type of adapter will depend on the type of phone.  After my first attempt at purchasing an adaptor failed, I contacted FLIR and they identified the specifications for the adaptor.  I needed an Type C OTG Adapter, USB C Female to Micro USB Male OTG (On the Go) Converter Charging Data Sync Adapter . It cost less than $10. 

Issues: The FLIR ONE app will occasionally freeze up or fail to recognize the attached camera.  This problem has become less common the more I use the camera.  The new FLIR ONE app is better than the original with some helpful videos on areas where the camera may be useful.  The variety of color pallets for viewing the image provides a way of selecting the best color temperature contrast. 

Supply air diffuser with spot temperature read out.  - N. Carlson

There will be more posts in the future as I get to know the instrument better.   

Cherry mold

Mold growth on red cherry - N.Carlson

Never pass up an opportunity to identify mold on food.  I purchased a bag of cherries a couple of days ago at a local grocery store.  The rest of the fruit I examined did not show mold growth.

I used a clear 3M red tartan Scotch tape with 85% lactic acid mixed with a small amount of lacto fuchsin stain. The photos were taken with a Samsung J7 camera using an AmScope microscope.

Growth of Alternaria spp. and Cladosporium spp. taken from a tease tape sample of the cherry - 400x - N. Carlson

This would be a fairly easy mold to identify for an introductory mold class.