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.