A common inhabitant of the human skin and upper airways, Staphylococcus aureus can also be a dangerous pathogen. For instance, this bacterium is a major cause of nosocomial infections and food poisoning. S. aureus cells frequently form multicellular structures called biofilms, thereby increasing their chances of withstanding diverse environmental challenges. This, together with the increasing rise in antibiotic resistance amongst S. aureus strains, has brought attention to the need to develop new eradication strategies. Bacteriophages are natural predators of bacteria and constitute a good alternative to traditional antibiotics and disinfectants. However, we still do not fully understand the interactions between phages and their bacterial hosts.
The aim of this work was to study biofilm development of S. aureus at subinhibitory doses of the lytic phage phiIPLA-RODI. This would provide information about possible scenarios that can easily occur when using bacteriophages as disinfectants.
Our results showed that certain phage to bacteria ratios (MOI, multiplicity of infection) can favour the development of a highly stable DNA-rich biofilm in some strains. Also, the biofilm-promoting MOI was related to the sensitivity of a given strain to phiIPLA-RODI. Interestingly, the release of extracellular DNA due to phage lysis did not seem to be the only explanation for this altered phenotype. In fact, transcription analysis performed by RT-qPCR revealed that phage-challenged biofilms overexpressed the gene encoding the major autolysin atl. It remains to be seen whether this response is a defense mechanism of the bacterial cells or an escapism strategy used by the phage, facilitating the action of its own endolysins.
Overall, our work emphasizes the importance of deciphering the bacterial responses to novel antimicrobials. This will ultimately allow the improvement of antibacterial products and application strategies to maximize efficacy and minimize undesired effects.