THEBIOMEDICAL SCIENCE SCIENCE THEBIOMEDICAL 26 SCIENTIST The big story The big story SCIENTIST 27 Fig. 1. Colonies of Streptococcus pyogenes, a gram-positive bacterium, growing on blood agar in a Petri dish. AN IDEA, A DESIGN AND A METAPHOR Andrea Sella, an award- winning chemist, broadcaster AUBIQUITOUS and classic science kit and equipment enthusiast, says: “The Petri dish has pretty much always stayed the same – there aren’t a lot of differences that you can make. I think the only real thing that has changed over the years is PIECE OF KIT standardisation. These days Petri dishes are very integrated How did the Petri dish first come pieces of equipment, with their standard sizes and their into being and was Richard Julius sterilised packs. “This evolution – the idea of Petri really the man responsible for the one-time, one-use, throw its creation? Stephen Mortlock away – is the only real change to what is essentially a 2D delves into the annals of microbiology. surface on which to grow a culture. It is a design classic – there is an elegant simplicity to the Petri dish and I don’t think it can be improved upon. cientists use them every day now made of disposable plastics and used “But the Petri dish exists in and discard them without a by labs around the globe for various more than one way: there is the second thought. They are studies in diverse fields. However, the item of equipment and then there is the meaning; the idea ubiquitous, disposable and Petri dish we know today did not start out of a Petri dish – it often disregarded. They are, this way. Enter Richard Julius Petri, a communicates the notion of life of course, Petri dishes. These German microbiologist, who in the late sciences in the same way that a well-known shallow and 19th century worked as an assistant to the bubbling test tube lidded plastic plates haves been celebrated German physician and communicates chemistry. “In the literal sense, it will used to grow bacterial cultures for many pioneering microbiologist, Robert Koch remain, as we are always Syears, serving a variety of uses, such as (1843-1910). At that time Koch, was thinking about the next testing the virulence of bacterial cultures considered to be, along with Pasteur and pathogen and you’ve got to or examining the efficacy of antibiotic Lister, one of the late nineteenth grow that pathogen drugs in development. century’s “fathers of microbiology” 5. somewhere. But I also think that the Petri dish has longevity When the scarlet fever bacteria, in the metaphoric sense. Streptococcus pyogenes, was found to Richard Julius Petri “It means ‘living laboratory’ grow in milk in the 1920s, studies were Richard Julius Petri was born in the and is used to signify any performed using Petri dishes to show the German city of Barmen near Wuppertal interesting experiments that are importance of keeping milk refrigerated 1. in 1852. He came from a distinguished taking place. I don’t think there’s an Other studies showed how Petri dishes, family of scholars and he was the eldest “The Petri dish exists in more than one equivalent. once inoculated with bacteria, could be son of Philipp Ulrich Martin Petri (1817- The Petri incubated in aerobic, micro-aerophilic 1864) a professor in Berlin and Louise way: there is the item of equipment and dish, as both and anaerobic conditions to grow a Petri (his father’s cousin). His paternal equipment variety of organisms or by adding a metal grandfather was Viktor Friedrich and idea, will then there is the meaning; the idea” be around for cover to prevent moisture loss and the Leberecht Petri (1782-1857), who was the a long time.” dehydration of the media 2-4. professor of classical literature and 1 The plates, originally made of glass, are Oriental languages and Director of the LIBRARY/ISTOCK PHOTO DOMAIN/SCIENCE PUBLIC WIKIPEDIA IMAGES: THEBIOMEDICAL SCIENCE SCIENCE THEBIOMEDICAL 28 SCIENTIST The big story The big story SCIENTIST 29 Fig. 2. Image taken in 1889, showing the action of an antibiotic compound on Bacillus anthracis bacteria cultured in a Petri dish. Fig. 3. Dr Robert Koch Fig. 4. Fanny Hesse 4 Collegium Carolinum in Braunschweig. year, describes the dish, but here it is used piece of Richard Petri enrolled at the Kaiser referred to as Koch’s plate method. The microbiological Wilhelm-Akademie for military English researcher, Percy Frankland JAMS AND JELLIES equipment. Recent physicians from 1871 to 1875. He then (1858-1946) also published a paper in 1886 While working at Koch’s laboratory, microbial cultivation undertook doctoral training as a in the proceedings of the royal society that Walther and Fanny Hesse (nee Eilshemius) technologies, however are starting to made their most famous contribution to subordinate physician at the Berlin described a flat-lidded dish 9. The general include highly subdivided multi-well microbiology – one that owed as much to Charité and received his doctorate in consensus now is that that it had been in Fanny’s skill with jams and jellies as plates and capillaries, as well as methods medicine in 1876 for his thesis “Versuche use for some time before Petri published Walther’s expertise with bacteria. Walther of sorting and counting encapsulated zur Chemie des Eiweissharns” (The his article, but he standardised the idea of Hesse (1846-1911) had trouble getting pure micro-colonies 10-11. By incorporating a Chemistry of Protein Urine Tests). a double dish with a larger lid. So effective cultures, so he confided his frustrations to printed, disposable colorimetric sensor his wife Fanny and she devised a solution. From 1876 until 1882 Petri practised as a was his idea that it had spread rapidly array into the Petri dish headspace, which She recalled that when she was growing up military physician, serving as a volunteer across Europe and once his paper in New York, they had a neighbour who had is responsive to the volatile substances with the 2nd Foot Guard Regiment. While appeared, the scientific community started lived for a time in Java. The neighbour emitted by microorganisms during serving as a military physician, he was naming it after him and the name stuck. taught her family about agar-agar, a growth, it is possible to detect the assigned to a research facility in Berlin, seaweed extract used in Asia to solidify presence of bacteria growing in the plate jellies and thicken soups. Fanny had been the Imperial Health Office, working with Moving on before colonies are visible 12. using agar-agar in her jams for years. Robert Koch. Not surprisingly, it was After leaving Koch’s laboratory, Petri Walther found that agar-agar was perfect Studies have also shown that nanospray during his tenure here that Petri acquired continued to be involved in bacteriology to solidify the beef broth. At 100°C, it could desorption electrospray ionization his interest in bacteriology. It is also and from 1882 to 1885 he became the head be melted, mixed with the liquid broth and imaging mass spectrometry can be used 2 where pioneering work on agar was of the Brehmerschen Göbersdorf poured into dishes. The new medium was for in vivo metabolic profiling of living solid at room temperature and above. undertaken (see box). sanatorium, administered by the Imperial bacterial colonies directly from the Petri Bacteria grew well on it but they could not 13 When Petri arrived at the lab, Koch’s Agar jelly more efficient experiments. The cover of Board of Health. He was a rather vain break it down. Agar-agar was even dish . Both of these can provide a fast assistants were already growing bacteria Another of Koch’s assistants, Fanny Hesse these new “Petri dishes” could stay on at disciplinarian who ran the tuberculosis translucent, which made identifying method for detection and identification in liquid broth, but Koch had realised the (1850-1934), introduced the use of agar all times to protect experiments from sanatorium on strict terms for staff and bacterial colonies and their to improve existing bacterial colony benefits of developing a solid culture jelly poured into a shallow glass dish kept contamination. Similarly, the cover was patients. In 1886 he became the Director of characteristics much easier. counting algorithms. And now Though it’s simply called media. He began by observing fungal under a bell jar, as a medium on which to transparent and as close as possible the Museum of Hygiene in Berlin, and in groups of researchers are agar now, the substance “colonies” growing on slices of potato. culture the bacteria. This jelly-like yet without touching the media or the 1889 he returned to the Kaiserliches used in microbiology making replacement organs Each colony was “pure”, containing solid substance provided a rich substrate experimental bacteria, ensuring one Gesundheitsamt as a Director from which labs is the same one in Petri dishes 14-15. But, too similar organisms. But this had for bacteria growth and because it was could easily observe the dish. he retired in 1900 with the title Geheimer that originated in often these systems require limitations. By placing liquid cultures in clear and the bacteria remained on the Regierungsrat (Privy Councellor). Fanny Hesse’s kitchen. expensive, sophisticated beef broth solidified with gelatin and surface, counting and identification The controversy In addition to his inventions and hardware that are often then cooling the solution, he was able to became much easier. But was it really Petri’s idea? As with all innovations, Petri published almost 150 specialised in application produce a clear, smooth, homogeneous But to observe the dish’s contents great scientific discoveries there is often papers on hygiene and bacteriology.