Have you ever thought about what could happen if microbes in your body joined forces?

Our microbiome, the collection of microbes on and within our body, is in many ways a collaboration between a huge range of microbes and us. We carry with us bacteria, fungi, viruses and archaea in our guts, on our skin and elsewhere in our body. By outcompeting invading microbes, or keeping opportunistic microbes in check, this collaboration keeps us healthy, aids in digestion and even influences our mood.

But what if microbes could collaborate to make us sick?

In a recent study, scientists found that some strains of Methicillin-resistant Staphylococcus aureus (better known as MRSA) have altered molecules on their surface that make it difficult for immune cells to recognize them.

Viruses known as phages infecting a bacterium. Credit: Design Cells.
Viruses known as phages infecting a bacterium. Credit: Design Cells.

How? These bacteria are infected with a phage, a virus that attacks bacteria. The phage makes the infected bacteria express several immune evasion genes, including a gene encoding an enzyme called TarP. TarP changes the surface molecules of MRSA, making it more difficult for our immune system to detect this bacteria. Importantly, TarP alters molecules that are potential targets for an MRSA vaccine. Two different phages named φtarP-Sa3int and φtarP-Sa9int can make MRSA produce TarP.

Curiously, the TarP-induced alteration of the MRSA bacterial surface also protects this bacteria from infection by certain other phages. This effect probably developed as a means for φtarP-Sa3int and φtarP-Sa9int to avoid competition with other viruses that target bacteria.

But the TarP-induced alteration of the MRSA bacterial surface could be bad news for us. Infection of MRSA with one of these phages could play a role in promoting infection.

MRSA can cause very serious infections that are difficult to treat. Our ability to cope with Staphylococcus aureus colonization is normally good enough to keep the bacteria from causing disease. We do not yet know if the phage in fact alters host-pathogen interactions enough to cause disease. As we learn more about how phages change the interactions between bacteria and our immune cells, looking for phages could become part of diagnostic strategies in the future. Looking for the presence of a phage with immune-altering properties could help physicians diagnose difficult-to-treat infections, or quickly identify strains of bacteria that will overcome vaccination.

Read the paper here!