**3. Conclusions**

We have known for decades that bacteria share some core genes (a common gene pool), so health professionals and microbiologists must consider the impact of commensal bacteria on pathogenesis and public health studies [5,7,9,10,86]. Moreover, non-pathogenic bacteria may contain virulence, drug resistance, and other non-housekeeping genes that are capable of increasing the pathogens' success during infection [6,11]. Furthermore, non-pathogenic cells that do not carry those genes may help pathogenic cells to receive those genes by amplifying their presence among microbiomes [7,27]. Finally, physical contact networks involving humans (see the above Sections 2.1 and 2.2) facilitate the pathogens' spread through our species. However, the vast majority of bacteria in human microbiomes, the non-pathogenic ones, must play critical roles in spreading virulence and resistance genes (Sections 2.3 and 2.4).

**Author Contributions:** F.D. and T.N. planned the paper. F.D. wrote the first draft of the manuscript, with contributions from all the other authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** Célia P. F. Domingues, João S. Rebelo, and Francisca Monteiro acknowledge FCT-Fundação para a Ciência e a Tecnologia, IP for their fellowships (PhD grants UI/BD/153078/2022, SFRH/BD/ 04631/2021 and PostDoc grant SFRH/BPD/123504/2016, respectively). FCT also supports cE3c by contract UIDP/00329/2020.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors thank the work of the editor and two anonymous reviewers.

**Conflicts of Interest:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
