The Most Correct Move

         The Bruker MALDI-TOF instrument is one of the most used tools at work. It provides rapid and mostly accurate identification of microorganisms. However, it does have its limitations. One of my colleagues came to me about a situation she encountered while running the instrument.

         The MALDI-TOF usually gives you the two best matches for organism ID. Most of the time, they are the same organisms. Sometimes, the second option is broader as it gives you a group. For example, an Enterobacter cloacae complex could be in that second option with a member of that group in the first.

         What you see in the image above is a rare scenario where the instrument gives you two different organisms with high confidence. As you can see, my colleague ran the patient sample in duplicates.

         A quick search on the internet yielded unuseful results for P. alcaliphila and P. composti. The former is a psychrophile and the other is something you'd find in a compost. Given the patient sample came from a leg wound, there was nothing to distinguish the two without more molecular or biochemical testing.

         While the colleague was preoccupied with what to do, I thought she was missing the forest for the trees. In other words, she was focusing on the wrong details.

         If you have read this far, you probably think this is a problem for reporting patient results. First, not knowing the organism's exact species doesn't stop us from performing susceptibility testing. Second, the two Pseudomonas species mentioned are not common pathogens.

         The most logical way to report on this patient is the "cop-out" answer: Pseudomonas species, not aeruginosa.

         If the clinicians want to know more, they could order more specific molecular or biochemical tests. For the treatment of the patient, it's largely irrelevant. As for us, we would attach the MALDI results in the composed text section and the workup log. If researchers want the organism for in-house research later, they would have the information in the database.

         My less-experienced coworker learned something that night. As laboratory personnel, we are there to provide data. The clinicians are the ones that would have to put together the puzzles to what's ailing the patients. Sometimes, some details are not worth our time to hammer out. The ones that don't are those that don't affect patient treatments.

Posted with STEMGeeks