During my third week in Microbiology, I again alternated between the primary and secondary benches. One of the main tests I performed throughout the week was the β-lactamase test for Staphylococcus aureus. S. aureus is a common bacteria found in many types of infections. Unfortunately, it is also known to be resistant to a multitude of antibiotics. The β-lactamase test is performed to see if the bacteria contains the enzyme, β-lactamase. This enzyme breaks down the β-lactam ring that certain antibiotics (such as penicillin) contain. This test is performed using a small disk that is placed on a slide, which is wetted with sterile water, and inoculated with the bacteria. The testing for the specimen is performed alongside quality control specimens that are known to be positive and negative. If the control organisms do not give the expected results, the test is invalid. A positive result appears as a pink color on the disk, whereas a negative result displays no color change. Continue reading →