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pathways and finally death.
The discovery and the development of new antibiotics from various Streptomyces and fungal species in the second half of the twentieth century was a milestone in medical history, saving millions of lives. Antibiotics were given as single compounds not only to millions of people but also to animals. This favored the development of resistance through target site modification (transporter, cell wall, ribosomal proteins, rRNA), enzymes that degrade antibiotics (β‐lactamase), enzymes that inactivate antibiotics, and ABC transporter (efflux pumps). Important resistance types are extended‐spectrum β‐lactamase (ESBL), New Delhi metallo‐β‐lactamase 1 (NDM‐1), AmpC (β‐lactamases), Klebsiella pneumoniae carbapenemase (KPC), vancomycin‐resistant enterococci (VRE), vancomycin‐resistant Staphylococcus aureus (VRSA), pristinamycin‐resistant S. aureus (PRSA), and methicillin‐resistant S. aureus (MRSA).
In the meantime, several pathogenic bacteria (e.g. Pseudomonas aeruginosa and S. aureus) have become increasingly resistant to effective antibiotics, causing thousands of death. This is why the development and production of new antibiotics should remain a high priority for the biotechnological industry. Also the development, of reliable and fast analytical devices, is a relevant area of biotechnology.
Organic low‐molecular‐weight compounds such as amino acids or recombinant proteins are often produced in bacteria (see Chapter 16). Sometimes, genetic manipulation of biosynthetic pathways can give a substantial boost to the yield (Chapter 31).
The human body harbors trillions (around 1014 cells) of bacteria, fungi, and protozoa from thousands of species in the gastrointestinal tract but also on skin and epithelia of mouth and vagina. This community is termed microbiota and their genomes the microbiome. The composition of the microbiota of an individual is due to variation, depending on age, food, health, and antibiotic use. The organisms in the microbiota show many ecological relationships with the human host, ranging from mutualism, commensalism, and parasitism. Using next generation sequencing (NGS) it is presently possible in a single analysis to obtain an overview, which species are present in the microbiota of an individual and in which abundance. Apparently, the composition of the microbiota plays an important and beneficial role for the health of an individual. It will be a challenge to manipulate the microbiota of an individual using fecal transplants or the administration of “good” microorganisms.
3.3 Structure of Viruses
Viruses (or phages when found in bacteria) are not autonomous organisms. Although they have some cell elements in common with bacteria (DNA or RNA as genetic information) (Table 3.7), they depend on host cells for their propagation. They invade bacterial, plant, or animal host cells to live as parasites. Excessive viral multiplication causes the death of host cells and thus disease in the host. The way how a virus enters the body and how it establishes itself in cells is very intricate and differs between virus and cell type.
Table 3.7 Classification of major animal and human pathogenic viruses.
| Class | Example/disease |
|---|---|
| I. dsDNA (double‐stranded DNA) | |
| Papilloma virus | Papilloma warts, cervical cancer |
| Adeno virus | Infections of the respiratory tract, tumors in animals |
| Herpes simplex virus 1 | HV I (blisters on skin), HV II (blisters on genitals) |
| Varicella zoster virus | Chicken pox, shingles |
| Epstein–Barr virus (EPV) | Mononucleosis, Burkitt lymphoma |
| Smallpox virus (variola) | Smallpox |
| II. ssDNA (single‐stranded DNA) | |
| Hepatitis B virus (HPV) | Hepatitis B |
| Parvovirus | “slapped‐cheek disease” |
| III. dsRNA (double‐stranded RNA) | |
| Reovirus | Diarrhea viruses, diseases of the respiratory tract |
| IV. ssRNA (working as mRNA) | |
| Poliovirus | Poliomyelitis |
| Rhinovirus | Common cold |
| Coronavirus | Common cold, respiratory disease, SARS, MERS, Covid‐19 |
| Hepatitis A virus | Hepatitis A |
| Hepatitis C virus | Hepatitis C |
| Yellow fever virus | Yellow fever |
| Togavirus | Rubella |
| West Nile virus | Flu‐like symptoms |
| Zika virus | Flu‐like symptoms |
| Dengue virus | Dengue fever |
| V. ssRNA (used as matrix for mRNA synthesis) | |
| Rhabdovirus | Rabies |
| Paramyxovirus | Measles, mumps |
| Influenza virus | Influenza viruses (H1N1, H5N1) |
| VI. ssRNA (used as matrix for DNA synthesis) | |
| Retrovirus | RNA tumor viruses, HIV (AIDS) |
Viral nucleic acid (Table 3.7) is enclosed by a protein envelope or capsid. Many viruses carry a biomembrane on the outside, which is derived from the host cell. It contains viral proteins (envelope proteins) that act as antigens. Viral proteins are often very variable. By modifying their surface antigen, whenever they multiply, they are able to outcompete the immune system, which cannot keep up the speed to produce the latest specific antibodies. Viral proteins are tailor‐made for each other. This enables them to spontaneously form supramolecular complexes and infectious viral particles.
Retroviruses, such as the HIV pathogen, are medically very significant (Table