“Can anybody explain this?”

The photo below was sent to me by Gavin Thomas, a microbiology scientist at Palmerston North in New Zealand.


Gavin (and me) would like to know the most likely cause of the “spots” on the plate. It was just the one plate that they appeared on.

Any hypotheses on the cause are most welcome, just add them to the comments section, regardless of how outlandish or ridiculous they might seem!

Equally, let me know if anyone else has seen a similar phenomenen on their plates.

Many thanks


p.s. Any other interesting plate (or other) pictures are most welcome to be submitted to the website. Just email me on michaeladdidle@gmail.com

6 thoughts on ““Can anybody explain this?”

  1. Hi Michael,
    I would suggest that there is a bacteriophage present in this culture that is killing off pockets of the bacteria.

    Kind regards,

  2. Yes, I agree with Murray. I have always been told that this phenomenon is due to bacteriophages. Sometimes the plates can look spotty all over like they have the measles. Adds a bit of interest to the sens plate reading.

  3. The phage theory is feasible too. I don’t recall having seen this double zone before but see this from wiki:

    The appearance of the plaque depends on the host strain, virus and the conditions. Highly virulent or lytic strains give clear plaques while strains that only kill a fraction of their hosts (due to partial resistance/lysogeny) or only reduce the rate of cell growth give turbid plaques. Some partially lysogenic phages give bull’s-eye plaques with spots or rings of growth in the middle of clear regions of complete lysis.

    1. Thank you all for excellent comments. I do remember someone telling me about phages causing this phenomenen about 10 years ago but had forgotten about it. I would agree that this is the most likely explanation.


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