Hello everyone, today I am going to discuss the process I went through to ID the bacteria present in my urine culture. I received MAC, SBA and CHROMagar plates already plated with the urine specimen. The specimen appeared as medium white-gray convex colonies on SBA, and nothing grew on MAC or CHROMagar. No growth on MAC led me to deduce that the isolate was not a gram negative rod, but since my isolate failed to grow on the CHROMagar, I had no way of knowing what the possible microscopic morphology of the isolate was or the possible ID of the organism. I was unable to proceed with any further biochemical testing since I didn’t know the microscopic morphology, so I decided to perform a gram stain. The gram stain revealed gram positive cocci in clusters. Knowing the microscopic morphology allowed me to proceed with testing. I performed a catalase test which was positive, a coagulase test which was negative, and a Novobiocin susceptibility test which revealed resistance. The results of these tests brought me to a final ID of Staphylococcus saprophyticus. The next day, after reincubating my CHROMagar, colonies grew. The colonies were pink and opaque. Pink opaque colonies correspond with Staphylococcus saprophyticus. Both pathways taken to identifying the organism brought me to the same conclusion. The lesson to be learned here is that there are multiple ways to arrive at the same ID, and if one method of identifying an organism fails, another can be used.
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| The middle colony growth is Staphylococcus saprophyticus . The picture at the very top is a gram stain of Staphylococcus. |
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