Practical Microbiology: The Indicative Smell

Practical Microbiology: The Indicative Smell

By Leonis | STEM stuff | 26 Jul 2020

         Well, the thing about working in an understaffed situation is that new hires are coming. And some of them have. Now, the training part could take a while. The fun part about training someone is that you get to know your new coworker. At the same time, share experiences relevant to the job.

         One of the major things lab technologists do is identifying pathogens. Outside of biochemical tests, etc., we use different clues to work towards a conclusion. One of such methods is the smell of the organisms. Of course, there is safety precautions to taking whiff, so that's a given.

         With the internet, it's often easy to find resources to use as aid for training. Here's an example of a chart I found to help with training.




         For the most part, I agree with the chart. There are some of them I would disagree with based on my experience.

For example:

Citrobacter - more of a brussel sprout smell. This is more true on chrome agar than not.

Corynebacterium - I have never encountered fruity smell on any plate.

Haemophilus - it has a smell, but doesn't seem to resemble wet far as the website suggests.

Nocardia - more of a rain smell. Instead of musty, it's actually a lot fresher.

Pseudomonas - can also smell like tortilla chips depending on the variant.

         An off chart example would be Staphylococcus saprophyticus. It shares the dirty sneaker/socks smell like S. aureus. On the chrome agar, the smell can be a differentiating point from other Staph species. Often, the smell is what sets S. saprophyticus and S. simulans apart on the chrome agar. Unless, of course, you choose to spend time using the MALDI-TOF to identify them for sure.


Why the smell?


         Sometimes, cultures can be messy. As in, several organisms can be present. Your sight may not always pick up all the different colonies that exist on the plate. Being able to pick out a distinct smell could help you find an organism you didn't see.

         On the efficiency side, you could save yourself some time and effort. This is especially true for some cultures where the susceptibilities are the focus. This also includes more preliminary information for the clinicians.

         Let's take the viridans group. Noticing that buttery smell helps you declare that you don't have S. pneumoniae. This is especially important in a respiratory culture.

         With Nocardia species, sometimes the smell come before you notice distinct colonies. This is one pathogen you want to pick out asap when dealing with blood cultures.

         I could go on and on, but the point is, smell can be a useful tool in microbiology. With the new dress code due to the pandemic, one should feel a bit safer taking a whiff. Everyone is pretty much in biohazard level 2 attire now.

         Anyways, it's another night at the lab.


The price of that wish ≒ a prelude to demise, a HIVE of souls ≒ moving VIBES

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