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CSIM2.2: BACTERIAL SHAPES, SIZES AND STRUCTURES 20/01/09 BASIC CLASSIFICATION OF ORGANISMS An organism is classified as any living thing, which includes both plants and animals All organisms are made up of one or more cells Organisms can be classified according to a fundamental structural aspect of their cell or cells: o Eukaryotes are organisms whose cells contain nuclei o Prokaryotes are those whose cells do not contain nuclei The prokaryotes are further divided into two domains: o Archaebacteria – primitive, often found in extreme environments, non-pathogenic o Eubacteria – essentially what are generally referred to as ‘bacteria’ LEARNING OUTCOMES Describe the major shapes and cellular aggregation patterns of bacteria Different types of bacteria can be identified through the properties of shape and aggregation pattern Common bacterial shapes include: o Coccus – spherical o Rod Bacillus – straight rods, may be single or in linear chains Vibrios – curved rods o Spirillum – rigid helices o Spirochete – flexible helices o Filamentous – long thin threads o Budding – with a stalk-like appendage Various prefixes to the cocci define their aggregation patterns: o Diplococcus – pairs o Streptococcus – linear chains o Staphylococcus – grape-like clusters o Tetrads – groups of four in a square arrangement o Sarcinae – groups of eight in a cubic arrangement The two most medically significant types of bacteria are: o Gram-positive – stain purple due to components of the cell wall retaining dye o Gram-negative – stain pink after decolourisation due to inability to retain dye