For a microbiologist, contamination in a nutrient broth tube or an agar plate is a nuisance. But sometimes, it’s a sign to stop and metaphorically smell the bacterial roses.
In the summer of 2019, microbiologists Greg McCallum, Rob Moran, Ross McInnes, and Stanley Ho—PhD students and lab mates at the University of Birmingham—noticed an unusual growth on an agar plate. Moran, then a postdoctoral researcher studying Enterococcus faecium, had left his agar plate on the lab bench for two weeks; during that time, something else grew alongside the white bacterial colonies.
This contaminant looked more like wire wool, running circles around the blood agar plate, and was featured in the 2023 Contam Calendar.
Laura Chatterley
As depicted in the above image, the growth was bright yellow and much bigger than its neighboring white clusters. “We all sort of gathered around it for ages. It was literally a like a pile of noodles,” said McCallum. But instead of immediately tossing the Petri dish into the trash, the group was deeply curious about this mysterious mass of noodles, which they promptly dubbed as Noodlomyces, and chose to investigate it further.
Greg shared images of their finding to Twitter, now X, which had an active community of microbiologists at the time. While some users chimed in on what it could be, the group probed Noodlomyces with a series of microbial techniques. When they performed a Gram stain and looked at it under the microscope, the culprit was revealed to be a round, cocci shape—thusly renamed as Noodlococcus.1 In addition to sharing these updates on Twitter, McCallum saw other people had shared their own contamination mysteries. Roughly a week after this began, they decided to make a separate account called Contamination Club (Contam Club) to post and reshare images.
“[Contam Club] ended up being quite a big community of microbiologists sharing contaminants. They're trying to find out what they were or just showing the beauty of microbiology and sort of how cool different colonies can look. It's underappreciated in microbiology by how beautiful some of it is,” said McCallum.
As microbe enthusiasts shared their images, the group began to brainstorm ideas about public engagement. So far, the group has mainly engaged with other scientists at conferences and other in-person events. McCallum noted that the group often received comments at conferences that Contam Club “made contamination from something that’s negative in the lab to be a positive thing” instead. Outside of the lab, though, he emphasized that contamination presented a unique hurdle to explain. “[The public think], ‘Well, you're trying to grow microbes. Why would it be a problem that microbes are growing in the lab?’” he said. To address this, McCallum and his lab mates go into the community to speak about their research, where McCallum also tacks on the topic of contaminants.
Other microbiologists found unusual food-related contamination on their agar plates. These dumpling-like colonies were featured in the 2023 Contam Calendar.
Elze Hesse
Aside from online posts and speaking at in-person events, both McCallum and Ho said that over time, they and other Contam Club followers wanted a way to physically showcase the images—whether as postcards, a coffee table book, or a calendar. They ultimately chose a calendar, curated a shortlist of images, and launched the first Contam Calendar in 2022. Since then, they’ve released a new edition each year.
Among the featured images were other food-like contaminants, including one resembling a small white dumpling. Others showed growths more akin to steel or wire wool, with circular loops repeating across the agar plate.
Since 2022, Contam Club has continued publishing its calendars while also revisiting earlier discoveries. Although Noodlococcus began as an unexpected side project, the group used a range of microbiological analyses and eventually published their findings on Noodlococcus in 2025.1 McCallum, now a postdoctoral researcher at the University of Liverpool, believes that fun, tangential projects like this are valuable to pursue. He said, “You can discover so much that might be useful to other people later.”
Now a postdoctoral research at the University of Hong Kong, Ho added, “For me, it’s a bit of a love letter to microbiology and that kind of curiosity you have as a kid, because you’re not doing it because of impact factors or to publish…you found this thing and you find it really cool.”
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- McCallum GE, et al. The Kocurious case of Noodlococcus: Genomic insights into Kocuria rhizophila from characterization of a laboratory contaminant. Microb Genom. 2025;11(10):001526.