Step 7: Success!
As you can see, printing with live E. coli cells worked perfectly! We probably let the colonies develop a little too long, so the letters are a bit fuzzy. We get a spray of small colonies from stray cells - probably due to some sputtering from the inkjet head. We may be able to improve on that by adjusting the viscosity or cell density of the culture we load into the cartridge.
But overall, not bad for a first try!
After printing, we disinfected surfaces with bleach, rinsed out the ink reservoir with bleach, and then let some bleach drip-flush through the print head, followed with a lot of deionized water, to make sure no bleach would dry up inside the print head.
It would probably be a good idea to invest in a second hand ultrasonic jewelry cleaner, so you can sonicate the heck out of any dead cells or other deposits that may form inside the print head.