As someone who has streaked many an agar-filled petri dish with sample swabs, I know how nasty the invisible, microscopic world around us is – finding numerous colonies of cultured microorganisms germinating from stairway rails, elevator buttons, toilet seats, door knobs, and other such ilk. It would disturb you to both know which one is unusually the cleanest surface as well as what is on them.
Today’s animated Google Doodle (Friday, May 31, 2013) honors the late Julius Richard Petri, a German microbiologist who is credited with inventing the Petri dish while working alongside bacteriologist Robert Koch in the Imperial Health Office in Berlin from 1877 to 1879.
On this day, back in 1852, Petri was born, thus the doodle commemorates his 161st birthday. During his lifetime, Petri practiced as a bacteriologists, a military physician, and a surgeon.
The inventor initially studied medicine at the Kaiser-Wilhelm-Academy for Military Physicians from 1871 to 1875, receiving his medical degree in 1876. He continued his studies at the Charité Hospital in Berlin, was on active duty as a military physician until 1882, and later continued on as a reservist.
Petri invented the standard culture dish, or Petri plate, and further developed the technique of agar culture to purify or clone bacterial colonies derived from single cells. This advance made it possible to identify the bacteria responsible for diseases. He died on December 20, 1921 at the age of 69 in Zeitz, Germany.
Petri dishes are primarily used in microbiology studies to culture cells, but have applications in other areas of science and medical research. These shallow plates can be made of glass or plastic and have cylindrical corresponding lids. Glass can be sterilized in an autoclave and reused, plastic are disposable.
Agar is a growth medium designed to support and encourage proliferation of microorganisms or cells. Nutrients and antibiotics can be added for selective experiments. Different types of growth media – such as blood agar, chocolate agar, Thayer-Martin, and Thiosulfate-citrate-bile salts-sucrose – are used depending on the application. Viruses, for example, require a medium containing living cells in order to propagate. Chocolate agar, a type of blood agar, is heated, lysed blood cells used to grow fastidious respiratory bacteria. Thayer-Martin (TM) is designed to isolate Neisseria gonorrhoeae.
When initially introducing a sample to the media, a technique known as streaking is employed – inoculating the surface in a methodic manner with a sterile loop or wire, resulting in a higher concentration to lower concentration colony spread.
Typically, Petri plates are incubated upside down (agar on top) to lessen the risk of contamination from settling airborne particles and to prevent water condensation from accumulating and disturbing the cultured microbes. They can be stacked atop one another.
The doodle consists of six animated Petri dishes. Once activated, a gloved hand streaks swab samples over each dish. After a moment each petri dish becomes soiled in appearance. When the cursor is hovered over each dish it shows the source of the sample contents: a smelly sock, a door knob, a computer keyboard, a panting dog, soil near a plant in the rain, and a sponge.
It is my best guess that E. coli (Escherichia coli) is the most predominant contaminant germinating in each one – visible after a brief incubation period.
[Image via Shutterstock]