Polymicrobial Infections and Biofilms

Dear Colleagues,

Deaths from common infections and wounds remained extremely common until the 19th century. However, the term infection did not exist. Diseases were thought to occur due to internal causes, disbalances and environmental factors. Bacteria, of course, had been known since the discoveries of Galileo and Leeuwenhoek in the 17th century. Nevertheless, no infectious potential was assigned to bacteria and their consequences for practical medicine were zero. For example, malaria translates to “bad air”.

The pathogenic role of bacteria was denied for simple reasons: they were thought to be too numerous and too widely present in unpredictably varying compositions.

Between 1864 and 1880, Pasteur and Koch demonstrated that bacteria are not present everywhere, and that their occurrence is not coincidental. Only some bacteria can be isolated from specific diseases and have the potential to cause the same disease in a healthy host after transmission. Based on this approach, numerous infections were described, with effective treatments developed in the 20th century. Starting in the 21st century, the discovery of new infections became rare. Anti-infectious therapies became more and more efficient, and the role of infections—as the cause of mortality—declined significantly. Cardio-vascular/neurologic/auto-immune/chronic inflammatory/metabolic disorders and cancer started to prevail. These were regarded as “internal” since specific pathogens seemed to be ruled out. This may be true for mono-infections, but what about polymicrobial infections?

If you ask a practicing physician to define the role of polymicrobial infections in their daily work, the spontaneous answer will be none! After a short reflection, they will, however, admit to being initially wrong and start listing that polymicrobial infections are substantially involved in vaginal disorders (vaginitis/vaginosis, etc.), prostatitis, tonsillitis, stomatitis, all kinds of wound infections, diabetic foot syndrome, different abscesses, sepsis, pyelonephritis, diverticulosis, appendicitis, chronic inflammatory bowel diseases, etc. They will probably also remember reading reports describing how molecular–genetic methods found complexly composed bacterial populations in the plaques of cardio-vascular disease and many other tissues, which were previously regarded as sterile. Moreover, they thought that many kinds of cancer were clearly associated with biofilms, and that complex microbiomes are important for shaping immunity, neuro- and endocrinology, and even behavior.

What exactly do we know about all these interactions with polymicrobial infections? In reality, we know little more than Leeuwenhoek did with regard to bacteria. Next-generation sequencing revealed the enormous variety of bacteria on all body surfaces in contact with the outer world. The composition of such microbiomes is markedly changed in different diseases, and these bacteria constantly migrate through our body. To understand polymicrobials, we must establish how exactly specific consortia are implemented. Modern molecular–genetic methods allow us to quantify participants, but it is time to unravel the pathogenic pathways involved, establishing how these single microbial groups work together, which of them suppress immunity, which break host boundaries, which are responsible for their spread, and how this spread is achieved. These investigations are long overdue.

Presently, there are at least five journals dedicated solely to Helicobacter pylori and none deal with polymicrobial infections. In this Special Issue, we aim to provide impetus to research in this direction.

Dr. Alexander Swidsinski
Dr. Sonja Swidsinski
Dr. Alexander Guschin
Guest Editors

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• polymicrobials
• pathogenic consortia
• biofilms
• human microbiome
• infectious background of “internal” diseases