Now some people see agar art as a waste of resources, time and money… but I think they are wrong. In order to produce something this incredible you have to know so much about bacteria and fungi, how they appear in different environments, how different agar affects them and how they interact with each other.
To produce a picture on agar out of bacteria and fungi you need to exploit a number of criteria such as organism colour, texture, colonial size and type of haemolysis as well as using inhibition to create various effects. Okay, it helps to be artistic as well (and I’ll show you my attempt at the end… prepare to laugh, it’s not in the ASM league!).
Colour can be used in two main ways either the bacterial pigments or changes that occur in the agar itself.
- Staphylococcus aureus – golden colour (hence the name aureus, the Latin for golden)
- Serratia marcescens – red (one of the theories as to why statues of the Virgin Mary can “cry blood”; it’s thought to be this Gram-negative bacterium growing on the statues!)
- Pseudomonas aeruginosa – various colours possible including green, blue, reddish brown (P. aeruginosa produces chemicals called pyoverdin - green, pyocyanin - blue and pyorubin – reddish brown)
- Coagulase negative Staphylococcus spp. – normally “boring” white (common contaminant) but great for making snowflake artwork
- Micrococcus luteus – lemon yellow (common contaminant)
- Rhodococcus equi – salmon pink (can cause severe infections in HIV positive patients and in horses causes foal fever)
- Rhodotorula spp. – red (this is the red waxy mould you sometimes see growing in showers)
- Chromobacter violaceum – purple (C. violaceum produces a pigmented antibiotic called Violacein which is a deep purple colour)
- Aspergillus niger – black (the spores of this fungus are black; it is an opportunistic pathogen)
These artists’ creations below use just one bacterium, S. marcescens (red) but I'm not sure what Mike Wazowski (Monster Inc.) is made of but I hope you agree the effect is quite striking!
- Blood agar – alpha and beta haemolysis of blood can give interesting art potential (alert! alert! the word interesting in a microbiology blog!!!); alpha haemolysis (e.g. Viridans Streptococcus spp.) gives a green colour whereas beta haemolysis (e.g. Streptococcus pyogenes) causes clear zones of complete haemolysis around the colonies
- Cysteine Lactose Electrolyte Deficient (CLED) agar is normally turquoise but goes yellow when bacteria ferment the sugar lactose to produce an acid, e.g. Escherichia coli, Klebsiella spp.
- MacConkey agar is normally an orange/red but goes bright pink when bacteria ferment the lactose in the agar, e.g. Escherichia coli, Klebsiella spp.
- Xylose Lysine Deoxycholate (XLD) agar is normally a rich red but some bacteria produce indole creating black colonies, e.g. Salmonella spp. and Proteus mirabilis
Using chromogenic agar is a way of taking colour to the next level!
This type of agar contains colourless compounds called chromogens which can be split by specific enzymes or chemicals to produce a pigment. The choice of chromogen can be used to detect an enzyme or chemical specific to a bacterial species and therefore the bacterial species itself. These types of indicator agar are used as screening agars for certain bacteria (e.g. MRSA agar) or to detect, quickly and cheaply, a limited array of bacterial species in a specific sample (e.g. UTI agar). Chromogenic UTI agar is especially good for agar art as different bacteria give different colours all on the same agar plate, it’s a bit like those wash-over colouring books you got as kids!
- E. coli = dark pink to reddish
- Enterococcus spp. = turquoise blue
- Klebsiella spp., Enterobacter spp., Citrobacter spp. = metallic blue
- Proteus mirabilis = brown halo
- Pseudomonas aeruginosa = cream, translucent
- S. aureus = golden, opaque, small
- Staphylococcus saprophyticus = pink, opaque, small
If you get it right with chromogenic agar, the variation of colours can be stunning:
It’s not just the colour of microorganisms you can creatively exploit, but their texture as well. Some bacteria are smooth, some are crinkled, some have a glassy appearance, others are mucoid and slimy and some eat into the agar itself creating a concave appearance to the art.
- Smooth – Staphylococcus spp.
- Crinkled – Actinomyces israelli
- Glassy – Bacillus spp.
- Mucoid – Pseudomonas aeruginosa
- Slimy – Klebsiella pneumoniae
- Eats agar – Eikenella corrodens
The final type of criteria that could be used to create agar art is the ability of microorganisms to inhibit each other. Most antimicrobials actually come from microorganisms and the truly great agar artists use these naturally occurring antimicrobial compounds to create clear zones between coloured colonies or to get colonial edges to heap up and change shape. Some of this is extraordinary; in the example below the yeast Saccharomyces cerevisiae is used in two forms, one producing an antifungal which inhibits another S. cerevisiae creating a clear zone with heaped up blue edges… wow!
Okay, it might seem frivolous and a waste of energy and resources but is it? Is all the knowledge gained a waste? I don’t think so… take a look at my agar art! Ermmmmmm… at least it’s recognisable!!! … “Is it a multi-eyed alien?” No it’s a Christmas tree!!! OK it’s certainly not going to win any competitions!?
Here’s a festive selection of agar creations from the Internet to inspire you… so you think you could do better?! Post your images up on our Facebook page for us all to see and comment on… (please respect decency standards! It’s not clever to make a phallic object using salmon pink Rhodococcus equi and Pseudomonas aeruginosa brown blobs!!!)