Did you know that bacteria can hide their antibiotic resistance?

Our recent study from UiT The Arctic University of Norway sheds light on this «hidden resistance». This phenomenon is often so rare that you cannot detect it through traditional testing methods, such as growing the bacteria in a Petri dish.

However, when the bacteria are exposed to antibiotic drugs during therapy, they can activate their hidden defensive equipment, rendering the patient's treatment ineffective.

Furthermore, bacteria can share their antibiotic resistance abilities with other bacteria, leading to the emergence of drug-resistant strains that threaten public health. It is as if they conspire against us in a secret brotherhood.

Such bacteria are not only a scary idea to contemplate. They actually keep popping up in many places around the world.

The secret of the bacteria

Detecting bacteria that carry hidden weapons can be a daunting task for even the most skilled laboratory technicians. They occur in numbers as scarce as one in a million bacteria, making it akin to searching for a needle in a haystack.

Only one in a million bacteria carry these hidden weapons, while we typically use 'only' ten thousand bacteria to do an observable traits test, a so-called phenotypic test, in the laboratory, where we grow the bacteria in a petri dish. But we would have to use a million bacteria to find the one with the secret super weapon.

You might think that it is not such a big problem when only so few bacteria carry hidden weapons. However, when you have an infection the number of bacteria multiplies rapidly, and soon there are more than a billion bacteria.

At that point, quite a few bacteria have hidden weapons against antibiotics. And still, they have yet another trick up their sleeve.

Whispering down the lane

When the bacteria notice that they are threatened by antibiotics, they bring out their secret weapon and ruin the effect of the medicine. But they can also share their blueprint of how to make these weapons with other bacteria.

They make numerous copies of the blueprint and share it with their mates around them. The result is that even more bacteria are now suddenly able to equip themselves with secret weapons.

And the patient is not recovering from the infection.

DNA – the secret storage

What can we do to detect and prevent the spread of such deceitful and dangerous bacteria? Most important of course is that you, as the reader of this article, only use antibiotics when you need them. Secondly, in the laboratory, we can combine traditional observable traits methods with methods looking at the genetic information of bacteria.

With methods such as PCR and genomic sequencing, we can peer at the innermost secrets of the bacteria. More specifically, we can have a look at their nucleic acids.

At the gene level, even bacteria can no longer hide their secret weapon blueprints.

Double testing

In Denmark and Canada, strains of enterococci with a hidden resistance capability managed to spread rapidly and cause disease outbreaks in hospitals. In Norway and Sweden, early detection, and more widespread use of genetic analysis of the Enterococcus’ DNA has so far prevented the spread of bacteria with hidden resistance.

In the next few years, we expect to find even more hidden resistance in bacteria. This means that hospitals and research communities must be alert and update methods to detect the bacteria’s secret weapons, and their blueprints.

Since we can only look for bacterial weapons that we already know about, we must continue research on other, and perhaps totally different defenses that the bacteria have hidden away - and that we still do not know about.

References

• Transiently silent acquired antimicrobial resistance: an emerging challenge in susceptibility testing
• A Silenced vanA Gene Cluster on a Transferable Plasmid Caused an Outbreak of Vancomycin-Variable Enterococci
• Alternative vanHAX promoters and increased vanA-plasmid copy number resurrect silenced glycopeptide resistance in Enterococcus faecium

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