What types of bacteria grow on bread?

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Bread that's stayed out too long or hasn't been properly stored usually grows mould at some point. Bread mould is commonly caused by different types of bacteria that can be harmful and even deadly if consumed in sufficient quantities. According to Scumdoctor.com, some researchers have concluded that these microorganisms can originate in the milk, flour, yeast and thus survive the baking process; others firmly disagree. Needless to say, never consume mouldy bread.


Penicillin is well known for being one of the most widely prescribed antibiotics in the world, but the fungus used to produce it, penicillium, is also a common bacterium that grows on bread. According to cmsynergy.com, this bacterium prefers colder environments, such as that found in your refrigerator, and will grow on fruit or bread. It will not grow, however, if the relative humidity in the air is less than 60 per cent. Penicillium bacteria form colonies that appear as fuzzy blue-green or grey patches on the bread surface.

Neurospora crassa

This bacterium species thrives on bread and produces spores on a 24-hour cycle. According to the National Institute of General Medical Sciences, neurospora crassa, "is simple to grow and has features that make it very suitable for answering questions about how species arise and adapt, as well as how cells and tissues change their shape in different environments." Neurospora crassa is red and produces tiny filaments along the surface of bread.

Rhizopus stolonifer

This common, fast-growing bacterium is a member of the phylum omycota and produces black mould. Rhizopus stolonifer is highly toxic and can destroy bread quickly by consuming nutrients found in the bread. This bacterium grows most rapidly at temperatures between 15 and 30 ºC. Rhizopus stolonifer spores are generally abundant in the atmosphere, and the bacterium will grow very quickly on bread stored in a relatively humid environment.


This common bacterium grows on cheese, decayed fruit and bread. It begins its life green and later turns to shades of reddish-yellow, yellow or reddish-brown. Ideal growing temperature range for aspergillus is between 22 to 30 ºC. This common bacterium grows quickly on bread kept in a moist atmosphere. Most aspergillus species are toxic to humans but some are common ingredients in pharmaceutical drugs.

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