MadSci Network: Microbiology

Re: How can I identify molds on bread?

Date: Mon Jan 2 07:37:58 2006
Posted By: Lynn Bry, MD/PhD, Dept. Pathology, Brigham & Women's Hospital, Harvard Medical School
Area of science: Microbiology
ID: 1136152406.Mi

Hi Ashley -

There are a number of websites with information about different species of molds, including images and drawings that can help you identify bread molds.

Doctor Fungus is one of my favorites.

You can also locate "Mycology" textbooks through your local public library, or a university library, which will give you the same information in printed form. If the library doesn't have a textbook in their collection, ask one of the librarians to help you locate a book via interlibrary loan. A few to try are:

When observing mold colonies on bread, you should define the following characteristics:
  1. What is the color of the mold? Some molds have hyphae (or branching elements) that are non-pigmented. These types of molds are called hyaline molds, whereas others (commonly the ones you see on the bathroom tiling) are "demetiaceous" or darkly pigmented - commonly black in color.
  2. Is the center of the mold a different color from the edges? Many light-colored molds, also called Hyphomycetes, produce pigmented spores as they grow. For instance, Aspergillus fumigatus produces a green center (coloration from the spores) with a white edge. The white edge is called an "apron" - this area has just hyphal elements (branches of mold filaments), that have not yet developed spores. Pencillium species tend to produce bluish-colored spores, while the spores produced by Aspergillus niger are black in color.
  3. Copious quantites of white-grey, cottony material suggests species of "Zygomycetes", namely Rhizopus, Mucor or Rhizomucor. In the lab, we refer to these species as "lid-lifters" as they will push the lid of a Petrie plate over if left to grow unchecked (for this reason, we tape the lid shut if we isolate one of these).
To speciate molds we commonly use a microscope to observe the fine structure of hyphae and fruiting bodies/spores produced. Biochemical assays are also commonly used. However, as you can see from above, simple observation of the mold colony can give you a good idea of the type of mold growing.

Lastly, molds need to be handled very carefully. The mold on bread is capable of causing infections, particularly in people with weakened immune systems, individuals with respiratory problems such as asthma, or in the very young or the elderly.

You should do the following when working with molds growing on foodstuffs:

  1. Wear gloves and an outer smock (or lab coat) when handling molds. Throw gloves our after use; smocks should be soaked in 10% bleach before washing and re-use.
  2. For observation, place materials in a clear plastic or glass container that can be sealed.
  3. Decontaminate all areas on which you have worked with the molds, or have placed molds, with a 10% bleach solution (to kill spores; 1 part bleach to 9 parts water). You can place this solution in a spray bottle to clean contaminated surfaces. Let the solution sit for ~10 minutes before wiping the area down.
  4. Foodstuffs containing molds can be fully soaked in 10% bleach for ~1 hour prior to disposal of the materials.

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