Fascinating day in lab today!

Today we pulled out our first plates of Serratia marcescans which some of the students used to redo the antiseptics/disinfectants lab. The cultures were bright red and fascinated the students. We used them to make wet mount slides and some of the kids chose to do Gram stains. They expected the bacteria themselves to be red, but they were gray, rod-shaped bacteria which Gram-stained negative. The red is just a pigment produced by the bacteria. I wonder why they produce that pigment. I'm looking, but haven't gotten the answer to that question yet. They are motile, though and some of ours could be seen moving since we did not heat set them in the wet mount slide. The kids loved it!

The zones of inhibition part of the lab was also interesting today. We pooled all the data and the hydrogen peroxide was again very effective (shown in the bottom quadrant in the picture above) as was the iodine-based pre-surgical sterilizer someone had brought from a hospital. Hand sanitizer was not very effective at all, much to the dismay of the students.

Bacillus stearothermophilus

The nutrient broth tubes of B. stearothermophilus I made last week show no discernable growth in an incubator set at 37 degrees C. So, today I streaked some nutrient agar plates with broth from those tubes as well as from the original agar slant that it came on from Carolina last week. Those slants have also been stored at 37C. I'm hoping elevating the temperature to 60-65 degrees C will promote growth, so I've uped the temp in one of the incubators. We'll see if that does anything. The only other issue is that I noticed the slants are actually on tryptic soy agar, so I'm not even sure B. stearothermophilus will grow on nutrient agar. Time will tell, I guess.

Switchgrass pathogens problems

Ok, so right now the switchgrass pathogens project is in dire straits. So far, I've been unsuccessful in growing uncontaminated cultures. I'm getting lots of bacteria in my cultures which ruins them. I looked for Rifampicin in all my supplier catalogs and didn't find any. (That's the antibiotic we put in the media at UT last summer to prevent bacterial growth.) I emailed UT to see if I can buy some from them and they aren't really set up to do that, but she told me I can buy some from Fisher Scientific. They have 250mg for $34 but it is in powder form. It is only soluble in things I cannot have in a high school lab, like chloroform. It is slightly soluble in acetone and methanol, so I may have to try that, but Fisher can't tell me how I make it into a liquid, so I'm back to the drawing board. My contact at UT did tell me I can put one drop of lactic acid into each petri dish as I pour my agar, and swirl it around to reduce the pH to a level where the bacteria will be inhibited, so I may have to try that. I'm getting a little flustered though. I just knew I could make this work for my students, and now I'm not so sure.

Nature of Science At Its BEST!

The kids were so excited about the results of this lab when we put them on the board today, that they want to continue this Antiseptic/Disinfectant Lab more next week. They want to streak the plates from all four directions and then test some new items. They chose to retest hydrogen peroxide (which seemed to inhibit growth best) and then add Lysol, hand sanitizer, Febreeze, and a cleaner called Recal that is used in the vet office one of the students works in. We talked about how typical this is in science. The more you learn about a topic, the more questions you have!

I did have enough growth (after a week) in my pathogen plates on water agar to make transfers onto PDA which is what I think I should have put them on to begin with. I still haven't ordered Rifampicin. It's $33 for a small quantity, so I may see if I can do without it. Dr. Ownley emailed me that I can use a drop of lactic acid in the PDA plates to lower the pH enough where bacteria don't do well, but fungi can still do OK. So, I may try that.

Antiseptic/Disinfectant Lab Results

Yesterday, the students observed their plates from this lab. We did not get full lawn growth on any plate. I think next semester, we need to streak the plates in all four directions instead of just in two. This would assure better coverage of the plates with organisms and I will be sure that any results we get were a result of the work of the antiseptic/disinfectant, not just poor streaking techniques. However, we were able to see some definite zones of inhibition which they thought was really cool! We also combined all of our data in a large table on the front whiteboard in the lab, which made for some very interesting comparisons. Be sure to do that again next time. When we look at this data in class today, it will be a great time to discuss the difference between observation and inference to teach Nature of Science.

Getting Ready for the Temperature Lab

Yesterday I received a freeze-dried sample of Streptococcus salivarius and a slant of Bacillus stearothermophilus from Carolina Biological. The freeze-dried sample was easy to revitalize except I really needed a 5mL pipette that was sterile. The only ones we had that were sterile were 10mL and that wouldn't fit into the container the sample came in. In my opinion, they should have shipped one with it or at least let you know that you must have one.

I also made nutrient broth cultures so the students can make culture transfers for me in class today after they finish the Antiseptic/Disinfectant lab. I mixed up 200 mL of nutrient broth to make the 12 tubes and probably had enough left over to do another 2-4 tubes. Each tube contains 10mL of broth.

I also did something different with the autoclave yesterday to speed up the process during 4th block. In the morning, I got the broth made, and aliquoted the broth into the tubes, and placed them into the incubator. I had already put water in the base. I got everything ready to go except putting the oil on the seal and placing the lid on the autoclave. About 1:30, I came into the lab and plugged in the autoclave, put oil on the seal, and put the lid on it so it could begin heating. I left the exhaust valve closed. At the very beginning of 4th block, I check on it and there was absolutely no danger. In fact, I could have probably turned it on 30 minutes earlier, but for sure another 15 minutes earlier wouldn't have hurt.

I need to make 800mL of nutrient agar today for the Temperature Lab for Monday. It takes 3 plates per group (one for each temperature). Probably 6 per group would be better, but I'm getting low on Petri dishes.

Antiseptic/Disinfectant Lab

We will do this lab today, but I don't have enough sterile filter paper circles for everyone to do their own petri dish. I have 50 that I purchased, but that would be enough for each group to do the lab together. I think I'm going to do one plate per person and use circles I cut out of coffee filters so everyone can have his/her own plate. I wish they had been sterilized, but it's too late for that. NEXT semester, I need to cut the circles and then autoclave them before the lab. I should have done that last week.

I am going to use Clorox, Quat 50, Iodine, 70% alcohol, 95% alcohol, and antibiotic ointment for them to choose their 4 antiseptics or disinfectants from.