Week 6

For the microbiome implant infection project that I am working on, we inoculate the mice with S. aureus during a knee implant surgery. Since the gut microbiome influences immunity, we expect that the severity of the implant infection will be affected by the mouse’s microbiome. Because of the amount of time needed for breeding, surgery, and analysis, unfortunately I won’t know the results of the study before I leave.  While we are waiting for the next round of surgeries, I spent the week working with the S. aureus strain and exploring some of the other experiments going on with different groups in the lab.

In the microbiome implant infection project, we use a specific clinical strain of S. aureus called Xen 36. I have found that this strain is a bit more difficult to work with than the more robust non-clinical strains I got used at Cold Spring Harbor. The Xen 36 colonies grow much slower and smaller on the agar plates than I am used to, and Xen 36 requires extra washing steps before measuring absorbance and inoculation. Talking to the other people in the lab, I wasn’t sure why the extra washing step was there. I was particularly interested in how the washing affected absorbance and growth, so the other interns and I set up a small experiment. I suspected that the washing removed a lot of the bacteria. We grew a liquid culture over two hours, and every twenty minutes we removed an aliquot to measure absorbance, wash, and measure absorbance again. The cultures had a significantly higher absorbance before washing compare to after washing. I think that the washing step removes a significant number of bacteria as well as any extracellular products the bacteria have produced. After some literature searches, we found that bacterial extracellular products can also boost the immune reaction. In an actual joint infection, you wouldn’t expect a fully mature liquid culture with extracellular products to infect a patient, just a couple isolated bacteria. To make the model as clinically relevant as possible, the cells must be washed before inoculation. Since I am only used to working with bacteria, I was focused on the bacterial growth. This was an important lesson to me to remember the bacteria host interaction.

I also got to see some cool procedures going on with other groups in the lab. One surgeon performed surgeries on a group of twenty mice to induce osteoarthritis. The most common methods for inducing osteoarthritis in a mouse model are surgical destabilization of the medial meniscus (DMM) and anterior cruciate ligament transection (ACLT). Both methods cause an instability in the knee that accelerates cartilage wear. I also got to see a method for DNA extraction using magnetic beads and how sections of bone get embedded in paraffin, sectioned with a microtome, and stained.

This week was more research focused because my mentor was away for part of the week at the conference. I’m excited to get back in the OR next week when he returns!