In each round of Dr. Microbe, you're presented with a challenge card that shows some combination of microbes and (possibly) a superbug. Each player has tweezers and a petri dish that's divided into three small sections and one large one. As soon as the card is revealed, players must race to place the microbes (and superbug, if present) in their petri dish. What's more, they must figure out which microbes (and possibly the superbug) to place in their petri dish based on this rule: The superbug must always be a different shape and color than the other three microbes in your dish! Whoever fills their dish with the proper items first claims the challenge card, and whoever first grabs five cards wins the game!
As a variant, you can play with the purple virus, which starts the game in the large petri dish that contains all of the other bits. You can grab this purple virus and place it in the petri dish of your left-hand neighbor, then that person can pass it left, etc. You can't end the round if the purple virus is in your petri dish! Whoever has the purple virus in their dish at the end of the round must give one of their previously collected cards to that round's winner.