Leeuwenhoek had stolen and peeped into the fantastic sub-visible world of little things, creatures that had lived, had bred, had battled, had died, completely hidden from and unknown to all men from the beginning of time. Beasts these were of a kind that ravaged and annihilated whole races of men ten million times larger than they were themselves. Beings these were, more terrible than fire-spitting dragons or hydra-headed monsters. They were silent assassins that murdered babies in warm cradles and kings in sheltered places. It was this invisible, insignificant, but implacable-and sometimes friendly- world Leeuwenhoek had looked into for the first time of all men of all countries. ~Microbe Hunters

Friday, 12 April 2013

Kirby-Bauer Test

The Kirby-Bauer Test is a type of antibiotic susceptibility testing (AST). It is done by isolating the pathogen that is causing infection in a patient, and streaking an agar growth plate with the specimen using a standardized turbidity of bacteria (0.5% McFarland standard). There are 2 things that you have to keep in mind when setting up this test. 1. You can’t leave the bacteria on the agar longer than 15 minutes before placing the disk of antibiotics on it, and 2. Once you place the disks on the plate, you must place them in an incubator within 15 minutes. Why? The action of the antibiotic disks is to create a concentration gradient of antibiotic around itself to inhibit the bacteria. After 24 hours, the circles of inhibition around the antibiotics are read to see what antibiotic the doctor should prescribe for the patient’s infection. If you wait too long to put the disk on, the bacteria can begin to grow (slowly) and they would have an advantage over the antibiotic. If you don’t put the plate in the incubator, then the antibiotic can diffuse faster creating a larger zone of inhibition without the bacteria growing in its optimal environment.

It is important to do ASTs and use the antibiotic with greatest effectiveness to not make “superbugs” in which the organism becomes resistant to the antibiotic. The overuse of antibiotics in today’s high-demand society has caused many organisms to become resistant to drugs that were once used to treat them. It has become standard practice to test susceptibility in the lab to help doctors treat the patient effectively. 

Also, do not flush old antibiotics down the toilet. Instead, take them back to your doctor. That way, they can reuse them for the next patient that comes in with a sore finger. Totally kidding. Never reuse antibiotics. Doctors know how to dispose of them properly. 

Darn good and sure of it,



  1. LOL. Reuse medication... Whew! That was a good one.

    1. I know, right?!? That's worse than if the bottle companies just refill the recycling and resell it!!