Why Does Mold Form on Food?

[Edgardo]

I'd like to know where mold comes from, for example
if you have food that you let outside a few days, then mold
is produced. But why?

Thanks in advance

 

[iansmith]

Molds are present in the environment. The mold spore will come in contact with the food by accident during the time you have the container open. Once the spore contacts the food, it sense that the environments is favorable for multiplication. A few days or weeks later you have a nice mold on your food.

 

[Monique]

Spores are very stable particles produced by molds that are dispersed into the air, these spores can germinate years after they are produced.

 

[misskitty]

What kind of mold grows on bread and makes it turn green? What other kinds of mold grow on food?

How did the scientist, who discovered penicillan (sp?), know it could be used effectively for treating illnesses?

 

[iansmith]

How did the scientist, who discovered penicillan (sp?), know it could be used effectively for treating illnesses?

the effect of penicillin was discover by mistake. The scientist, Alexander Flemming, had poor aseptic techniques and poor waste disposal habits. One day he was cleanning plates that were left on the bench for a while. He was examinating everyone of them until he saw that a no bacteria were present around a mold in the familly of the Penicillium. He then try a few experience and some people were able to isolate the active compound.

Actually people have know about the antiseptic use of mold for centuries. In some eastern europe countries, it was a tradition to keep a bread with mold and to apply a slice of this bread on wound.

 

[Ouabache]

Molds are very much like plants, just cannot photosynthesize (no green color). And like plants, produce reproductive structures. Molds may produce spores, conidia, schlerotia etc . These resting structures are microscopic which is why you don't see them landing on your piece of bread..

Monique is correct, that many of these resting structures will survive over long periods of time. Plants produce microscopic spores too (e.g. ferns, mosses, pine trees)

The most common bread mold is Rhizopus a black mold
see ---> http://www.backyardnature.net/f/bredmold.htm
also see dark spores
---> http://www.skidmore.edu/academics/biology/plant_bio/fungi/Rhizopus - bread mold.jpg

The Penicillium species, are more common on citrus fruits
see ---> http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/penicill.htm
also see their fruiting structure with spores strung together on top ---> http://www.botany.utoronto.ca/ResearchLabs/MallochLab/Malloch/Moulds/Illustrations/Penicillium.jpg

iansmith is correct that penicillin was discovered by accident.. I believe they were culturing bacteria (Staphylococci) and some penicillium mold spores contaminated their plates.
After incubation, they noticed the bacteria didn't grow within a zone surrounding the mold colonies. The mold must have been releasing something into the culture medium that inhibited bacterial growth.

Side note: Because bacteria have very short life cycles, their evolution is accelerated. Mistakes in their DNA sequence occur and are passed onto next generation. Some of these mutations allow them to survive when penicillin is present in your body, and those bacteria will multiply quickly. A good example of survival of the fittest. So it's best not to rely too strongly on one antibiotic, because their will be selection pressure for resistant bacteria and soon the antiobiotic no longer works.

 

[iansmith]

What kind of mold grows on bread and makes it turn green? What other kinds of mold grow on food?

Mold can be green and Cladosporidium can be an olive-green to olive-brown in colour. this is most likely the type of mold you will find in your food because the Cladosporidium are one of the most common mold.

The Green colour, however, is not due to chlorophyll as Ouabache point it out. colour found on mold are often due to secondary metabolites or other secreted compounds.

I believe they were culturing bacteria (Staphylococci)

Yes it was and more specifically Staphylococcus aureus

How Fleming discover penicillin

Both of Fleming's discoveries happened entirely by accident during the 1920s. The first, lysozyme, was discovered after mucus from his nose dropped into a bacterium laced Petri dish (he sneezed). A few days later, it was noted that bacteria where the mucus had fallen had been destroyed.

Fleming's labs were usually in disarray, which led to be to his advantage. In September 1928, he was sorting through the many idle experiments strewn about his lab. He inspected each specimen before discarding it and noticed an interesting fungal colony had grown as a contaminant on one of the agar plates streaked with the bacterium Staphylococcus aureus. Fleming inspected the Petri dish further and found that the bacterial colonies around the fungus were transparent because their cells were lysing. Lysis is the breakdown of cells, and in this case, potentially harmful bacteria. The importance was immediately recognized, however the discovery was still underestimated. Fleming issued a publication about penicillin in the British Journal of Experimental Pathology in 1929.

http://en.wikipedia.org/wiki/Alexander_Fleming

We are lucky he was not working with E. coli, it is naturally resistant to penicillin. But it might have plated the wrong culture at some point

 

[Monique]

The Green colour, however, is not due to chlorophyll as Ouabache point it out. colour found on mold are often due to secondary metabolites or other secreted compounds.

The color in molds is often related to melanin: it protects the mold from UV damage by absorbing the radiation http://www.rastafarian.net/melanin2.jpg

 

[misskitty]

I didn't know there are some European cultures that keep moldy pieces of bread to put on wounds. Did it actually work?

 

[iansmith]

I don't think they keep moldy bread anymore but there is account from 18-19 century West european traveling to some east european countries that observed reduce infection of the wound when moldy bread was applied. I just can't remember the reference my prof told us

Several fungi that grow on bread produce antibiotics. It would work. I just don't know how safe it is nowadays. However, back in those i would have taken the risk.