Introduction of Colony Characteristics
Colony characteristics or morphology of bacteria is the most common diagnostic method in bacteriology for isolation and identification of bacteria on the basis of phenotypic characteristics on solid medium for the color, shape, surfaces, size, elevation, edges, opacity, and consistency.
Common colony characteristics of bacteria
Colony morphology of bacteria on the basis of the following features:
- Size
- Shape
- Elevation
- Margin or edge
- color
- Surface appearance
- Density
- Consistency
- Hemolysis
- Odor
- Pigmentation
Size
It is of three types on the basis of the diameter of the colony.
Large: Diameter of colony larger than 1 mm
Medium: 1 mm in diameter.
Small: Less than 1 mm in diameter.
Shape
It is of the following types-
- Circular
- Filamentous
- Irregular
- Punctiform
- Rhizoid
- Spindle
Elevation
Elevation of the colony is of the following types-
- Flat
- Raised
- Convex
- Umbonate
- Dome-shaped
- Umbilicate
Margin
The margin of the colony is further divided into
- Entire
- Undulate
- Lobate
- Erose
- Filamentous
- Curled
Color
The color of the colony are following types-
- Yellow
- White
- Black
- Cream
- Pink
- Red
- Blue
- Red etc.
Surface appearance
The surface appearance of the colony may be-
- Glistening
- Smooth
- Granular
- Dull
- Rough
- Creamy
Density
Colony density is the ability to see through the colony. On this basis is of following types-
- Opaque: It can not see through the colony.
- Transparent: It can see through the colony.
- Translucent: It can only see with light shining through.
Consistency
Consistency of colony is best observed by picking up a colony with a loop or needle. It is of the following types-
- Butyrous (buttery)
- Brittle
- Viscid (sticky)
- Friable (Crumbles easily)
- Membranous (pliable)
Hemolysis
It is best observable in 5 % sheep blood agar. It is of three types-
- Alpha (α) hemolysis
- Beta (β) hemolysis
- Gamma (γ) hemolysis
Odor
According to smell, it is of the following types-
- Sweetish
- Aromatic
- Fishy
- Seminal
- Others
Pigmentation
Some bacteria produce pigments and are of the following types-
- Golden yellow (Staphylococcus aureus)
- Lemmon yellow (Micrococcus luteus)
- Prodigiosin( pink/red/ magenata): e.g. Serratia marcescens
- Pyocyanin (bluish-green) e.g. Pseudomonas aeruginosa
- Pyoverdin/fluorescein (greenish-yellow) e.g. Pseudomonas aeruginosa
- Pyomelanin (brown to black pigment) e.g. Pseudomonas aeruginosa
- Pyorubrin (red): e.g. Pseudomonas aeruginosa
Bibliography on Colony Characteristics
- Clinical Microbiology Procedures Handbook- Lynne S. Garcia, Second Edition update
- Topley and Wilson’s microbiology and microbial infection- Bacteriology-2-10th Edn.
- Manual of Clinical Microbiology-Patrick R. Murray -8th Edn.
- Bailey and Scott’s Diagnostic Microbiology -13th Edn.
- Mackie & Mc Cartney Practical Medical Microbiology – 14th Edn.
- Diagnostic Microbiology-Connie R. Mahon & George Manuselis
- Koneman Color Atlas and Text-Book of Diagnostic -Microbiology-6th Edn.
- Jawetz Melnick and Adelberg’s Medical Microbiology-25th Edn.
- Lippincott’s –Illustrated- review-Microbiology-3rd Edn.
- Mandell’s Infectious Disease-7th Edn.