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Summary Introduction into bacteriology
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Molecular Basis of Bacterial Infections Evelien FloorIntroduction into the field of
bacteriology
Introduction
All species on earth can be divided into three domains of life: archaea, bacteria and eukarya. There
are almost 50.000 different bacterial species known of witch 200 are pathogens. However, the
estimated number of bacterial species is over 15 million. Bacteriology belongs to the field of
microbiology. However, the field of microbiology is much wider (acellular: viruses, prions. Cellular:
archaea, fungi).
Antoni van Leeuwenhoek was the first one who described bacteria. He was able to visualize them
with his own made microscope. He called the bacteria “animalcules”, which means little animals. The
genus bacterium (“little stick”) was first described by Christian Gottfried Ehrenberg. This genus
included non-spore forming rods whose relation to other species was obscure. Later this was
changed to the genus Bacillus by Ferdinand Crohn to describe them as spore-forming, Gram-positive,
aerobic or anaerobic bacteria. Other founders of the field of bacteriology are Louis Pasteur and
Robert Koch.
Bacteriology can be divided into different groups:
General bacteriology
o Focus on biological science
o Basic microbiology: cytology, genetics, and physiology
Applied bacteriology
o Focus on applications
o Industrial: agriculture, food, beverages, pharmaceuticals, biotechnology
o Environmental: soil, marine
o Clinical: veterinary and human disease (medical bacteriology)
Medical bacteriology
o Focus on infection and clinical (human) application
o Amongst largest departments in hospitals (interdisciplinary)
o Often research and diagnostics linked
o Research fields: host/pathogen interactions, antibiotic (resistance)
Classification of bacteria
Bacteria come in many different shapes, arrangements, and sizes and there is no uniform way to
classify them. There are three ways of classification:
1. Phenotype
o Morphology and arrangement (shape)
o Cell wall
Gram stain
Motility (flagella)
Capsule
Spore formation
o Oxygen requirements
o Nutrients/metabolism
2. Genotype
o Genes and genomes
3. Phylogenic
o Evolutionary relatedness (rRNA)
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, Molecular Basis of Bacterial Infections Evelien Floor
Phenotype
Phenotype classification can be based on morphology and arrangement. Classification is also possible
based on the cell wall for instance via Gram staining. Acid fast mycobacteria do not stain with Gram
staining so additional staining is developed for these species. Additional staining’s are spore staining,
capsule staining, and flagella staining. These characteristics can also be used for classification.
Another way of classification is based on nutrients and metabolism. Bacteria require an energy (ATP),
carbon and electron source to survive. Energy and carbon can be obtained in two ways. Autotrophs
use CO2 to create their own carbon source and energy. They can either be photosynthetic (light) or
chemosynthetic (chemical compounds in the environment). Heterotrophs derive energy from
breaking down complex organic compounds taken from the environment.
Bacterial classification is also possible based on oxygen requirements. Aerobic bacteria thrive in the
presence of oxygen. Anaerobic bacteria cannot tolerate gaseous oxygen. Oxygen can be toxic for
bacteria; aerobic bacteria therefore need enzymes to break down the toxic oxygen products. SOD is
an enzyme that breaks down those oxygen products. Catalase is a common enzyme found in nearly
all living organisms exposed to oxygen.
Genotype
Bacteria do not contain a nucleus (prokaryote), DNA can be found in the nucleoid. The chromosomal
DNA is generally one circular molecule, sometimes multiple or linear. The plasmid DNA is
extrachromosomal DNA, linear or circular. Plasmids aren’t essential but can give advantage to the
bacteria.
Phylogenic
Phylogenic classification is based on 16s ribosomal RNA gene expression.
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