Introduction to Microbiology

Introduction to Microbiology

• Microbiology is the study of microorganisms that exist in unicellular, multicellular, or acellular forms and must be viewed individually with the aid of a microscope.
• Microorganisms include eukaryotes, prokaryotes, viruses, viroids, and prions.

Branches of Microbiology

• Bacteriology: study of bacteria
• Mycology: study of fungi
• Virology: study of viruses
• Parasitological: study of parasites
• Protozoology: study of protozoa
• Immunology: study of the immune system
• Microbial genetics: study of the genetics of microorganisms
• Recombinant DNA technology: study of genetic engineering

Applied Microbiology

• Medicine: vaccine development, production of antibiotics, and biological enzymes
• Industry: production of beer, wine, cheese, and yogurt
• Agriculture: maintenance of soil fertility, improvement of plant growth and productivity
• Veterinary microbiology: study of veterinary medicine and vaccines
• Environmental microbiology: study of the role of microorganisms in maintaining ecosystem balance and their use in ecosystem improvement

Eukaryotes

• Characteristics: organisms with cells that have a nucleus and other membrane-bound organelles
• Examples: animals, plants, algae, nematodes, fungi, and protozoa

Prokaryotes

• Characteristics: unicellular organisms that lack a membrane-bound nucleus and other membrane-bound organelles
• Examples: bacteria and archaea

Archaea

• Characteristics: prokaryotes with ether linkages in their cell membrane, lacking peptidoglycan in their cell walls, and having genes and enzymes similar to those of eukaryotes
• Differences from bacteria: cell membrane, cell wall, and RNA polymerase

Plasmid

• Definition: a small, circular, extra double-stranded DNA molecule that is distinct from a cell's chromosomal DNA
• Characteristics: can replicate independently, usually small, and contains additional genes that may be useful to the organism under certain conditions

Cytoskeleton

• Definition: a complex network of interlinking filaments and tubules that extends throughout the cytoplasm
• Functions: provides shape to the cell, helps in mitosis by chromosomal separation

Virus

• Definition: an acellular, ultramicroscopic, metabolically inert, infectious agent that replicates only within the cells of living hosts
• Characteristics: contains either RNA or DNA, has a protein coat called the capsid, and may have an envelope of lipids and proteins
• Functions: attaches to and enters host cells, replicates, and assembles into new viral particles

Prions

• Definition: proteinaceous infectious particles composed of abnormally folded protein
• Characteristics: causes disease similar to viral infection, attached to normal proteins inside neurons, and causes them to take on the shape of the prion, leading to disease
• Examples: Creutzfeldt-Jakob disease, fatal familial insomnia, and kuru

Viroids

• Definition: small, circular RNA molecules without a protein coat
• Characteristics: replicate through a rolling circle mechanism, cause diseases in plants, and are "sub-viruses"

Vaccine

• Definition: a product that stimulates a person's immune system to produce immunity against a specific disease
• Types: live, attenuated, inactivated, subunit, toxoid, and conjugate vaccines

Immunity

• Definition: specific defenses against a particular disease
• Types: active immunity (following clinical infection or vaccination) and passive immunity (transfer of maternal antibodies or administration of immunoglobulin or antiserum)

Immunizing Agents

• Vaccines: stimulate the production of antibodies and provide immunity against one or more diseases
• Immunoglobulins: provide immediate immunity against a specific disease
• Antisera: provide immediate immunity against a specific disease

Types of Vaccines

• Live, attenuated vaccines: contain a weakened form of the living microbe, elicit strong cellular and antibody responses, and often confer lifelong immunity with only one or two doses
• Inactivated vaccines or killed vaccines: contain a killed form of the disease-causing microbe, stimulate a weaker immune system response, and may require several doses
• Subunit vaccines: contain a fragment of the microbe, rather than the entire microbe, and stimulate an immune response
• Toxoid vaccines: contain inactivated toxic compounds that cause illness, rather than the microbe itself
• Conjugate vaccines: contain a polysaccharide outer coat linked to a protein, which leads to recognition of the polysaccharide as a protein antigen
• Recombinant vector vaccines: use a manipulated microorganism to transport genes to cells to code for a needed protein or hormone