A recent development at work is identifying all (possible) Corynebacterium in a culture. By recent, I mean within the last 12 months. For the most part, these gram positive rods tend to be harmless. In fact, they are commensal. Most of the times, we could chalk it up as normal flora unless it's in a respiratory culture.
Your basic club-looking gpb you could find on a Wiki page.
The occasions where they could cause issues, the most notable is C. diphtheriae. Some of you might remember the hard membranes that caused suffocation. But, I'm sure many of you have received vaccinations against that particular bacteria. Often, it's in combination with tetanus and pertussis.
What's worse is its toxins: https://en.wikipedia.org/wiki/Diphtheria_toxin.
In short, it causes complications and destroy many of the cells in your body. Imagine your cells melting in a slow, agonizing, acidic bath.
So, what do you have to fear if you are already vaccinated against C. diphtheriae? Well, the joke is on you because life happens. There exist other Corynebacterium species that can produce the said toxin. In this case, C. ulcernan and C. pseudotuberculosis. They are similar enough that it shouldn't be a surprise they could deliver the same problems.
There have been documentations in the 80s of certain toxigenic variants. Meaning, it wasn't a common occurrence. Over time, I suppose it has become more and more prevalent. Or, is it because we didn't have the technology we have today to identify risks?
In that paper from 2012, researchers saw C. ulcernan as an emerging pathogen. Here's the best part, with possible zoonotic potential. So, the next time you hear about "diphtheria" in a diagnosis, it might not be from the traditional bacteria.
Like I said before, life finds a way. Nature has things evolved to find new approaches to kill you the same way.
So what does the lab do?
The lab picks out suspicious small, white/gray colonies (more so than most other bacteria) on a culture. Then, the MALDI-TOF can identify the species with high accuracy. The clinicians can decide whether they are significant or require more testing.
I tried to search for some culture pictures, but they all seem unhelpful. The most useful snapshots are the ones that show you what this genus looks like when mixed in with other flora.
That study is from last year. It's a recent development that they are looking into more rapid identification. In particular, whether the said Corynebacterium has toxigenic potential.
While it's extra work for lab personnel, it's not overcomplicated. And it could help physicians evaluate risks for the patient. It's not uncommon to find the bacteria on the patient's body before they actually infect them.
In my career, I have only seen one case of diphtheria through lab work. The case involved C. diphtheriae, so this is all new to me. In this field, you do see how practices change as the organisms evolve. I remember my boss recalls the days when Pseudomonas weren't as antibiotic resistant. Nowadays, it can be one of the most resistant germs you find in a culture, causing all sorts of problems.
Anyways, the point is that other germs can cause "diphtheria".