Microbes: Fungus and Bacteria – Intrinsically Linked


I probably don’t need to say this, but did you know that fungi can kill bacteria?   Most antibiotics used today were found originally in fungi, although many of these chemicals are now synthesized in factories.  Strictly speaking, antibiotics are substances made by microorganisms that stop growth of other microbes or kill them outright. The first ever antibiotic to be discovered was penicillin, by Alexander Flemming in 1929, although it would take another ten years before it was introduced to the medical profession as a viable cure for all sorts of diseases.

Antibiotics work by attacking single cell bacteria cells, sometimes by interfering with transfer of chemical messages essential to the bacteria’s reproduction (erythromycin) or  by blocking formation of the bacterium’s protective cell wall and preventing its reproduction (penicillin).   Either way the bacteria is unable to reproduce and slowly die out:




The story goes that Fleming, a professor of bacteriology at London University’s St. Mary’s Hospital, was studying a dangerous bacterial genus called Staphylococcus, which is the cause of staph infections, and was growing it in a gelatinous nutrient material in petri dishes. He had been on vacation and returned to find something odd in a dish accidentally left in the open.

The bacteria had multiplied, forming colonies across the gel. But Fleming noticed a furry, green mold colony at one edge. Around it, the bacterial colonies had died. It looked as if the mold was emitting a substance that killed nearby bacteria:

peni plus bac


I gave the following book to the children to read.  There may be better ones out there but our library was selling it for 5p!


We had already tried to grow penicillin by placing some orange skins into a ziplock bag.  This was recommended on a website, and I blithely followed.  Fungi are primarily aerobic microorganisms although if there is no oxygen available they become what is known a facultatively anaerobic.  However, when we placed our orange peel in the baggy, we limited the oxygen supply.  Two weeks later we checked on the bag, expecting it to have a greeny/blue hue.  What we found was the orange peel in almost the same condition we had left it in bar some red growths on the surface.  In fact the most noticeable change was conspicuous only by its absence.  Whatever the red microorganism was it had used up all the oxygen reserve, sucking the bag tightly closed against itself.  There was no evidence what so ever of any penicillium spores:


It was a bit disappointing to have failed in growing what we had aimed to grow.  None of us were able to identify the red growth.  Any clue anyone?

Our failure to thrive microbially speaking continued into our next experiment.  We wanted to test the efficacy of some antibiotics.  We first used an antibiotic swab used for cleaning wounds.  We prepared two petri dishes, plus a control, with re-prepared agar (we used the left overs from our last experiment, remelting it and pouring into the petri dishes).  Using a Q-tip we zigzagged some microorganism containing residue from the top of our sink (the dirtiest place in our kitchen).  After this we placed a clean square of gauze on to the agar in one petri dish, before placing the antibiotic swab gauze on the second dish, labelling as we went:


My issue with this was that the antibiotic swab seemed to contain its antibiotics in a thick Vaseline type material.  So I meddled.  I couldn’t help myself.  My daughter was on the very antibiotic we had failed to grow.  So I stole a tiny pipette full (we had been told we had more than she needed and to throw the rest) and squirted it onto the Vaselined swab:


And we left them for three weeks.  Three weeks because after one week there was little change; after two weeks there was little change and after three weeks we noted a small amount of fungal growth in the petri dish with the antibiotic in:


There was no bacterial growth that we could see in either of the petri dishes.  We concluded that the agar was not viable for growth anymore, having heated and reused the left overs from last time.  It was a bit disappointing, although I guess we did still learn something (never reheat and reuse agar!).

However, we soon got talking about how we could maybe try our hand using this or this as a guide to grow penicillin.  We would remake some fresh agar and after the penicillium had happily multiplied in aerobic, dark bliss we would use it to see if it prevented the growth of bacteria from our mouths (which we are kind of hoping might contain the Staphylococcus bacteria which Fleming was said to have been working on (25-30% of the population has it).

I was thinking we could pop some spores of the Penicillium onto one side of the agar after smearing it with mouth contents.  Yes gross, but I refuse to be beaten by a single-celled organism!

So we grew, successfully this time, some penicillin fungus:


We swabbed T12’s mouth hoping to catch some lovely gram positive bacteria which would not thrive in the presence of penicillin:


T zigzagged the swab over the entire surface of the petri dish:


You can see from the photo above that I had drawn a dividing line on the bottom side of the petri dish.  This would allow us to scrape some penicillin from the lemon onto one side of the agar, leaving the other free from the fungus:



So we ended up with a petri dish with absolutely nothing done to it, a petri dish swabbed with T’s mouth bacteria and a petri dish containing T’s mouth bacteria over the whole surface with half containing the home-grown penicillin fungus:


We placed them in a warm, dark place in our laundry cupboard.  Here they are after one week:


Yuck!  Most of what you can see is condensation on the lids, but the fungus seemed to have just died out, or at least did not grow any more at all.  The control had the least bacterial growth which was expected; the petri dish which contained just the mouth swab did have the most colonies growing, but not by much and the one with the penicillin did not show a definite area where the fungus could have been said to obviously inhibit the growth of the bacteria.  All in all a bit of a disappointment, and we’re not entirely sure why.  Just to remind you what it should have looked like:


And you’ll see we failed miserably.  Alas, I was beaten by a single cell organism!  This wasn’t an entirely wasted effort though.  I think when the children carry out experiments such as these the stuff that matters is generally not forgotten easily.  Whilst the GCSE syllabus did not require us to go to such depths, I think the fact we have will help with their retention should they choose to take the exam.  At least, that is what I am hoping for.

I have a couple more microbe posts to come, after which we will be moving on to classification.  No more growing yucky microbes.  I’m not unhappy about that.



  1. If it’s any consolation, my science experiments at school never worked either. I remember one experiment where I knew I was meant to get a pH result of neutral (green) and the solution was steadfastly staying bright yellow. In the end I squeezed some blue ink out of my fountain pen into the test tube…

  2. Sometimes the best learning comes from those experiments that don’t turn out as we expected. We have had a few of those ourselves. I love May’s comment about adding ink. That is too funny. We did an experiment with an apple. One piece was supposed to turn brown and one wasn’t. Neither turned brown. Now on any other day, any apple would turn brown as exposed to air. At least that is my experience. Oh, well.

    Have a great day on this home school journey…

    Hugs to you, Claire.

      1. Yes, apples goes brown remarkably well on their own accord. did you put them in a sealed baggy – maybe it’s the air which makes them go brown?
        I’m just waiting for T to realise I have that picture up of him and to be given a big telling off! He gets them in his inbox so it won’t be long….

    1. I’m stubborn like that…..
      I was considering trying yet again (being slightly annoyed that it wasn’t doing what it ought) but I soon came to my senses!

  3. It’s so easy to grow fungus and microbes when we aren’t trying in the summer months – I can see why it would be disappointing not to get the ones you want! (Love the pic of T swabbing his mouth!)

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