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Module: BIOM - 1009

Lecturer: Dr Bonab

Date: 14/10/16

Taxonomy of Microbes Part 2
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Phenotypic characteristics can be used to identify microorganisms without the need for sophisticated
equipment
 This includes the size and shape
 This can allow quick identification
 Based on size and shape, the organism can be split in to:
 Prokaryote, fungus or protozoan

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The Gram stain differentiates between Gram positive and Gram negative bacteria
 It rapidly narrows the number of possible organisms
 However, the Gram stain alone is not enough
 Streptococcus pyogenes, for example, cannot be distinguished from streptococci that are
part of the normal throat microbiota
 In certain cases, the Gram stain result is enough to start antibiotic treatment
 For example, a Gram stain of sputum showing numerous white blood cells and Gram
positive diplococci is highly suggestive of Streptococcus pneumoniae
 In other cases, the Gram stain can be enough for diagnosis
 The presence of Gram negative diplococci clustered in white blood cells in a sample of a
urethral secretion from a man is highly suggestive of Gonorrhoea

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Certain microorganisms can be identified using special stains
 For example, acid-fast bacteria can be quickly identified using the Ziehl-Neelsen stain

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The morphology of the colony can give initial clues to identify the problem
 For example, Serratia marcescens are often red due to the production of pigment
 Other morphological features include:
 Shape
 Margin
 Elevation
 Texture

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The metabolic capabilities can give clues to the organism’s identity, some such capabilities include:
 The type of sugars it ferments
 The end products it makes

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Biochemical tests can be conducted to determine an isolates metabolic capabilities, some are fast, some
can take at least 18 hours to incubate
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coli such as E

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