about bacteria How to dilute pills(powder) and

[deleted-59032]

Hello,
I am working on a science fair project titled, "The effect of Antibiotics(prescription vs. non prescription) on Bacterial Resistance" and I have a pill called clindamycin that I need to dillute to 10mg/ml. The pill is 300mg and I do not have a scale available to measure in mg. Also, I ordered e.coli (k-12 strand) from carolina science supply and it came in a tube in a solid form. Am I supposed to do something to make this into a liquid form before use? If so, how do I do it? If you can help in any type of way as soon as possible, it would be greatly appreciated.

Kind Regards,
Taylor

[deleted-71820]

Hi -
Dilutions are easy once you know how to work with them. 10mg/ml means that in each milliliter of liquid there are 10mg of powder. The first thing to do, however, is figure out what your diluent is - water, PBS (that's basically saline), and ethanol are common. If you do not have a way to measure out things on the mg scale, my advice would be to take the entire 300mg and dilute to 10mg/ml. The calculation would be:
(300mg) / (10mg/ml) = 30ml
So, you would take the entire 300mg and dilute in 30ml and wait for it to dissolve. For most antibiotics you can store them in aliquots at -20C (that's a freezer) without losing potency (they should be in small aliquots because multiple freeze-thaw cycles will cause most drugs to lose potency), but double check on this particular one. If you are unsure, contact the manufacturer.

As far as the bacteria - Did the company send you information on what to do with it (usually they do)? Did this come in an agar stab? If this is the product you're talking about:
http://www.carolina.com/product/escheri ... estMatches

it looks like an agar stab. That means that the bacteria is in the agar.

What you should do at this point depends on what you want to do with the bacteria. If you are directly plating onto agar plates to make a bacterial lawn, then using sterile technique, take a sterile inoculating loop and gently scrape the surface of the agar stab, then take the loop and dip into sterile growth media (usually LB, but could be different for this bacterial strain). You don't need to dig into the agar, a very small amount of starting bacteria will be fine. Because the average doubling time of bacteria at the right growth conditions is 20 minutes, the cultures grow exponentially, meaning that a very small amount of starting material grown overnight will result in billions of bacterial cells. This will result in a suspension of bacteria in the LB. Remember to keep everything sterile, you don't want to contaminate with other bacteria! Then grow the inoculated media, usually overnight, usually shaking at 37C and then next day spread evenly onto LB plates and let grow overnight at 37C. You might not need so much bacteria for your experiment, so growth times can be anywhere from 5 hours to overnight. Check your protocol. This type of technique would be useful if you were testing different antibiotics by placing a disc (could be sterile filter paper or something like that) soaked in each antibiotic (and remember to include controls!) onto the plate to see a zone of antibiotic activity surrounding the disc.

Or, if you are doing an agar streak, you would take an inoculating loop and gently scrape the surface of the agar stab, then gently streak the loop across the surface of an agar plate in kind of a criss-cross pattern. It looks like ScienceBuddies has a document with instructions on how to do this (attached). This is useful if you want to get single bacterial colonies.

Good luck!
Stephanie

[deleted-59032]

Thank you sooooooo much. That was a HUGE help!:)