Tuesday, September 22, 2015
This post is the first for some time - as a retired microbiologist, I now have a lot of work on my hands, though it is much more varied than when I was working full-time. Indeed, I wonder how I ever found time to go to work!
I thought I would give readers a little present as thanks for continuing to follow Safe Food. The post is only indirectly about safe food, but I hope you will allow me a little whimsy.
Modern culture media contain various indicators that change the colour of the agar or stain bacterial colonies in ways that allow the microbiologist to presumptively identify the bacteria. This has led the more artistic microbiologists to use bacteria to draw on the agars. Recently, this art form has blossomed, to the extent that the American Society for Microbiology runs a competition for the best image. I posted a more primitive image at Christmas time last year http://foodsafetywithjaybee.blogspot.co.nz/2014/12/fungi-for-christmas.html
I particularly liked this beautiful drawing done on Hektoen Agar, which is used for isolating Gram-negative enteric pathogens. I reproduce the image and description from the ASM website, unchanged, below:
A moderately selective differential medium, Hektoen is used in the isolation Gram negative enteric pathogens, particularly Salmonella and Shigella. Bile salts inhibit Gram positive and some non-pathogenic Gram negative organisms, making the medium partially selective. Lactose, sucrose and salicin aid in the colour differentiation of colonies. Being non-fermenters of these compounds, Salmonella and Shigella don't change the color of the pH indicator system, whereas some organisms like Escherichia coli change the colour to yellow or orange, fermenting one or more of these compounds to acids. Ferric ammonium citrate in this medium enables the detection of H2S production by Salmonella. This picture exhibits its differentiating characteristic with Salmonella grown into a Black butterfly and E.coli, a yellow flower and few stripes in the butterfly.
Of course, Salmonella, Shigella and some strains of E. coli can all cause enteric disease, and it is important to be able to isolate them and identify them if they occur in foods.
I don't know the artist's name, but I have the feeling that some post-graduates have too much time on their hands!