Bacteriophages

Bacteriophages were discovered in 1917 by the Canadian Felix D'Herelle. Already in the 2nd World War various bacterial infections were fought with bacteriophage preparations. The antibiotic penicillin, discovered in 1928, and subsequent antibiotics, however, completely displaced the more complex bacteriophage therapy. However, due to their specificity for certain bacteria, phages still represent a conceivable alternative to antibiotics today in the wake of increasing resistance to antibiotics (Domingo-Calap P et al. 2016).

Bacteriophages (short: phages) are viruses with an average size between 30 to 200 nm. They consist only of genetic material and a protein coat. Like other viruses, bacteriophages also show a different appearance. Thus, there are icosahedral (twenty-sided) phages (e.g. Phi X 174) or filamentous (filamentous) phages (e.g. M13 phage).

Reproduction: Bacteriophages can only reproduce in bacteria. After attachment to a bacterium and after their penetration, the phage DNA is introduced into the cell. The protein coat of the bacteriophage either remains on the surface or fuses with the bacterial cell wall. Bacteriophages can be integrated into the bacterial genome (transduction), or they remain extrachromosomal (episomal). Often the bacteriophage genome carries information for toxins e.g. the diphtheria toxin of Corynebacterium diphtheriae or the scarlet toxin of Streptococcus pyogenes. When the genetic material of a bacteriophage is replicated in a bacterium, fragments of the bacterial DNA can be incorporated into the phage and thus later transferred to other bacteria(transduction). In this way, the information present on it can help the bacterium to acquire new properties(phage conversion).

Once bacteriophage replication is complete, the cell walls of the infected bacteria are either destroyed (lysed) to release the new phages, or the new bacteriophages are cut off from the cell wall of the bacteria.

Bacteriophages have adapted to a specific bacterial species or even to a specific group within a species. They are host specific. This host specificity has led to bacteriophages becoming instruments of research. Phages are already used in genetic engineering (they are used as "gene taxis", i.e. phages are used as vehicles to introduce specific DNA segments into bacterial cells. In addition, phages are also used for vaccine production, as gene/drug carriers for bacterial detection and typing. Furthermore, phages are used in food preservation in many countries. Also as antibiotics substitute phages are in versch. (Krylov VN et al. 2019; Domingo-Calap P et al. 2016).