Chapter 1: The Microbial World and You
1.1 Microbes in Our Lives
- Microbes that live stably in and on the human body are called the human microbiome, or microbiota.
- Many factors influence where and whether a microbe can indefinitely colonize the body as benign normal microbiota or be only a fleeting member of its community (known as transient microbiota).
1.2 Naming and Classifying Microorganisms
- Bacteria (singular: bacterium) are relatively simple, single-celled (unicellular) organisms.
- Because their genetic material is not enclosed in a special nuclear membrane, bacterial cells are called prokaryotes.
- Like bacteria, archaea consist of prokaryotic cells, but if they have cell walls, the walls lack peptidoglycan.
- Fungi are eukaryotes, organisms whose cells have a distinct nucleus containing the cell’s genetic material (DNA), surrounded by a special envelope called the nuclear membrane.
- Protozoa (singular: protozoan) are unicellular eukaryotic microbes.
- Algae (singular: alga) are photosynthetic eukaryotes with a wide variety of shapes and both sexual and asexual reproductive forms.
- Animal parasites are eukaryotes. ==The two major groups of parasitic worms are the flatworms and the roundworms, collectively called helminths==.
1.3 A Brief History
- Hooke’s discovery marked the beginning of the cell theory— the theory that all living things are composed of cells.
- Until the second half of the nineteenth century, many scientists and philosophers believed that some forms of life could arise spontaneously from nonliving matter; they called this hypothetical process spontaneous generation.
- In 1858 Rudolf Virchow challenged the case for spontaneous generation with the concept of biogenesis, hypothesizing that living cells arise only from preexisting living cells.
- These discoveries form the basis of aseptic techniques, procedures that prevent contamination by unwanted microorganisms, which are now the standard practice in laboratories and many medical procedures.
- Koch thus established Koch’s postulates, a sequence of experimental steps for directly relating a specific microbe to a specific disease
- The protection from disease provided by vaccination (or by recovery from the disease itself) is called immunity.
- Treatment of disease by using chemical substances is called chemotherapy.
- Chemicals produced naturally by bacteria and fungi that act against other microorganisms are called antibiotics.
- Chemotherapeutic agents prepared from chemicals in the laboratory are called synthetic drugs.
- Bacteriology, the study of bacteria, began with van Leeuwenhoek’s first examination of tooth scrapings.
- Mycology, the study of fungi, includes medical, agricultural, and ecological branches.
- Parasitology is the study of protozoa and parasitic worms.
- The study of viruses, virology, originated during the First Golden Age of Microbiology.
- ==Microbial genetics== ==studies the mechanisms by which microorganisms inherit traits, and molecular biology looks at how genetic information is carried in molecules of DNA.==
- Genomics is the study of all of an organism’s genes, scientists are able to classify bacteria and fungi according to their genetic relationships with other bacteria, fungi, and protozoa.
- Recombinant DNA (rDNA) technology inserts recombinant DNA into bacteria (or other microbes) to make large quantities of a desired protein.
1.4 Microbes and Human Welfare
- Microbial ecology, the study of the relationship between microorganisms and their environment, originated with the work of these scientists.
- By using bacteria in these ways—a process known as bioremediation—toxins can be removed from underground wells, chemical spills, toxic waste sites, and oil spills, such as the massive oil spill from a British Petroleum offshore drilling rig in the Gulf of Mexico in 2010.
- A very exciting and important outcome of recombinant DNA techniques is gene therapy—inserting a missing gene or replacing a defective one in human cells.
1.5 Microbes and Human Disease
- This latter mode of behavior is called a biofilm, a complex aggregation of microbes.
- An infectious disease is a disease in which pathogens invade a susceptible host, such as a human or an animal.
- Since 2014, there have been 1800 confirmed human cases and 630 deaths caused by a new virus called Middle East respiratory syndrome coronavirus.
- Because the first reported cases were linked to the Middle East, this latest emerging infectious disease is called Middle East respiratory syndrome.
- H1N1 influenza (flu), also known as swine flu, is a type of influenza caused by a new virus called influenza H1N1.
- Avian influenza A (H5N1), or bird flu, caught the attention of the public in 2003, when it killed millions of poultry and 24 people in southeast Asia.
- In the 1980s, methicillin-resistant S. aureus, called MRSA, emerged and became endemic in many hospitals, leading to increasing use of vancomycin.
- First detected in 1995, Ebola virus disease causes fever, hemorrhaging, and blood clotting in vessels.
- Recorded cases of Marburg virus, another hemorrhagic fever virus, are rare.