All Notes

Colony Morphology of Bacteria: Introduction, Types and Special Features of Bacteria

Introduction of Colony Morphology

Colony morphology of bacteria is the most common diagnostic method in bacteriology for the 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.

Fig. Non-lactose fermenting colony (colorless) of Pseudomonas aeruginosa (upper) and mucoid lactose fermenting colony (pink) of Klebsiella pneumoniae (lower)

Common Colony Characteristics of Bacteria

Colony morphology of bacteria on the basis of the following features:

  1. Size
  2. Shape
  3. Elevation
  4. Margin or edge
  5. color
  6. Surface appearance
  7. Density
  8. Consistency
  9. Hemolysis
  10. Odor
  11. 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 is the 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 the 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/ magenta): 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

Colony Morphology of Bacteria-Related Photos

Small size colony of bacteria

Fig. Small size colony of bacteria

Large size colony of bacteria

Fig. Large size colony of bacteria (Klebsiella pneumoniae)

Beta-hemolytic colony of streptococci on blood agar

Fig. Beta-hemolytic colony of streptococci on blood agar

Prodigiosin pigment of Serratia marcescens

Fig. Prodigiosin pigment of Serratia marcescens

Pyoverdin Pigment of Pseudomonas aeruginosa on Muller-Hinton agar

Fig. Pyoverdin Pigment of Pseudomonas aeruginosa on Muller-Hinton agar

Pyocyanin and pyorubrin pigments of Pseudomonas aeruginosa

Fig. Pyocyanin and pyorubrin pigments of Pseudomonas aeruginosa

Micrococcus luteus yellow color colony on nutrient agar

Fig. Micrococcus luteus yellow color colony on nutrient agar

Micrococcus roseus red colony on a nutrient agar plate

Fig. Micrococcus roseus red colony on a nutrient agar plate

Bibliography

  1. Clinical Microbiology Procedures Handbook- Lynne S. Garcia, Second Edition update
  2. Topley and Wilson’s microbiology and microbial infection- Bacteriology-2-10th Edn.
  3. Manual of Clinical   Microbiology-Patrick R. Murray -8th Edn.
  4. Bailey and Scott’s  Diagnostic Microbiology  -13th   Edn.
  5. Mackie & Mc Cartney  Practical Medical Microbiology – 14th  Edn.
  6. Diagnostic Microbiology-Connie R. Mahon & George Manuselis
  7. Koneman Color Atlas and Text-Book of Diagnostic -Microbiology-6th  Edn.
  8. Jawetz Melnick and Adelberg’s Medical Microbiology-25th Edn.
  9. Lippincott’s –Illustrated- review-Microbiology-3rd Edn.
  10. Mandell’s Infectious Disease-7th Edn.
Medical Lab Notes

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