Morphology

Refers to either the appearance of colonies on media or the appearance of individual organisms in the microscope.

Colony Morphology (see diagrams below)

Shape

• circular
• irregular
• radiate (radial ridges)
• rhizoid (irregularly branched)
• spreading
• swarming

Proteus mirabilis swarming on blood agar

Size

in mm, or pinpoint

Texture

• granular
• dry (chalky)
• friable (crumbly)
• mucoid
• butyrous (like butter)

Surface

• smooth
• dull
• glistening
• beaten-copper (small craters)
• ground-glass (tanslucent and refractile)
• wrinkled

Colour

Edge

• entire (even)
• lobate (in lobes)
• undulate (wavy)
• erose (irregularly toothed)
• fimbriate (fringed)
• effuse (thin, spreading)
• rhizoid (feathery)

Elevation

• flat
• raised
• convex
• umbonate (raised button in centre)
• draughtsman (flattened in centre with raised edges)

Opacity

• transparent
• translucent
• opaque

Odour

• present
• absent
• resembles?

Haemolysis on blood agar ( see also entry on haemolysis in general glossary)

α, β or none

Cellular Morphology

Colour

• gram positive (purple)
• gram negative (pink)

Shape

• Coccus (plural=cocci)
• Bacillus (plural=bacilli)
• Straight, curved or spiral
• Ends: rounded, square, pointed

Size

• large
• small

Arrangement

• single
• pairs
• clumps
• tetrads
• palisades (side by side)
• chains (end to end)

Spores

• Present or absent
• Central or terminal
• Causing distension of cell or not

Other descriptors

• Beaded- crystal violet concentrated in spots along length of bacteria
• Bipolar – stain concentrated at each end of cell
• Branching – cells bifurcate
• Coryneform- club shaped
• Fusiform- long, thin cells pointed at each end
• Pleiomorphic – variable appearance (shape/arrangement)
• Variable – both gram positive and negative individuals