Introduction to Microbiology

What are microorganisms (microbes, “germs” or “bugs”)?

• living things individually too small to be seen with the naked eye; individually minute because the “body” of  one microorganism consists of a single cell or just a few cells
• include bacteria, some fungi (yeasts & molds), protozoa, microscopic algae & parasitic animals as well as viruses (note: viruses are acellular entities at the border of life & nonlife)

Microbes’ distinctive traits

• ancient, appear to be earth’s only inhabitants for 2B years
• ubiquitous, found nearly everywhere, as free-living microbes or parasites of host organisms; no doubt outnumber macroscopic organisms by a factor of several million & extremely diverse

Harmful impact of microbes on humans

• Pathogens (causing infectious diseases: still widespread, many emerging & many thought to be noninfectious may be infectious after all) 
• Note: “Host manipulation” e.g., by rabies virus

Malaria            Syphilis          Infectious         Flu virus

parasite           bacteria         yeast

Harmful impact of microbes on humans

• Food-spoilers – as much as 20% of food lost due to spoilage
• Note: Microbes may be producing the nasty smell of spoiled food to keep large animals away!   

Harmful impact of microbes on humans

• Destructive biofilms that cause clogging of water pipes or medical implants such as joint prostheses & catheters, dental plaques that may lead to tooth decay.

Beneficial impact of microbes on humans

• Produces food  for humans and eaten by many other organisms, e.g., planktons eaten by whales form the base of food chain in marine ecosystems

Other beneficial impact of microbes on humans

• Decomposers that release nutrients for plants  (composting)
• Sewage treatment to recycle water
• Bioremediation to clean up pollutants
• Biocontrol of pests
• Used in the chemical/pharmaceutical & biotechnology industry

What about human impact on the microbial world?

• driving force in the evolution of antibiotic-resistant pathogens

Human impact on the microbial world

• Genetic modification of microbes via biotechnology
• Changes in microbial community structure, e.g., biofilms growing on man-made structures compared to biofilms on natural habitats
• Yet uninvestigated human consequences…

Three domain system (Woese 1978): based on     phylogenetic relationships; reconstructed using rRNA sequence

Phylogeny of all life:

                    Domain           Domain        Domain

                    Bacteria          Archea         Eukarya

                           |                     |__________|                   

                           |________________|

                                          |

• Note: Viruses are in a group of their own; not truly alive (reproductive entities but acellular)

Naming and classifying microorganisms: 

“Scientific name” – a unique name assigned to one type of  organism (species)

It consists of  the “genus” name and the “species” name; while genus names  are always UNIQUE to particular genera, species names are not.

Genus is the smallest taxonomic grouping of  different species.

The first letter of  the genus name is ALWAYS capitalized, species names are not.

The scientific name is properly written UNDERLINED or printed ITALICIZED

Naming and classifying microorganisms: 

e.g.,  scientific names in Domain Bacteria 

              Staphylococcus aureus            

              Escherichia coli                   

              Mycobacterium tuberculosis

e.g.,  scientific names in Domain Eukarya

             Kingdom Fungi

                   Saccharomyces cervisiae (Baker’s yeast)

                        Kingdom  Animalia

                   Homo sapiens

• Discovery of  microbes (called “animalcules” by Van Leeuwenhoek, 1673) using the first microscopes
• Rejection of  theory of  spontaneous generation (Pasteur, 1861) in favor of  theory of biogenesis

• Food Microbiology
  • Development of techniques for fermentation

                                                         (Pasteur, 1857)

• • pasteurization (Pasteur, 1864)

Medical Microbiology (late 1800s

• Bacterial endospores & sterilization: “sterile” environment requires destruction of heat-resistant endospores
• Lister introduced “aseptic techniques” to reduce microbes in a medical setting & prevent wound infections
• Germ theory of disease: microorganisms cause disease (Koch, 1876); note Koch’s postulates; Pasteur also worked on the same problem
• Pasteur’s (1880) discovery of why vaccinations (such as Jenner’s smallpox vaccine or the ancient Chinese’ technique)  worked: loss of virulence by pathogens
• Discovery of the “magic bullet” (chemotherapy)
• Ehrlich (1910) found a chemotherapeutic agent (medicine) against syphilis
• Chemotherapy
• Fleming (1928) discovered antibiotics which he called “penicillin” from a mold called Penicillium notatum