
how can morphology of colony identify bacteria?
how can morphology of colony identify bacteria?
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Colony morphology means the visible features of bacterial colonies on solid media and it’s fundamental for preliminary identification because each species often has unique traits.
Key characteristics include:
Form (shape): e.g., circular, irregular, filamentous, rhizoid.
Size: measured in millimeters; terms like punctiform (<1 mm) vs large colonies aid classification.
Margin (edge): describe as smooth (entire), undulate, lobate, filiform, curled, scalloped, serrated.
Elevation: observed from plate side—flat, raised, convex, pulvinate, umbonate, umbilicate.
Color/pigmentation (chromogenesis): includes pigment diffusing into medium; notable examples include Serratia marcescens red pigment or Pseudomonas aeruginosa green pigment.
Opacity: transparent, translucent, opaque, or iridescent.
Surface texture: smooth, glistening, rough, dull, wrinkled.
Consistency: creamy (butyrous), sticky (viscid or mucoid), dry/brittle (friable).
Hemolysis patterns observed on blood agar (alpha green‑ish, beta clear‑zone, gamma none) help differentiate streptococci and staph species.
Odour, while optional, can be diagnostic (e.g., grape‑like Pseudomonas aeruginosa).
Procedure:
- Incubate plates (usually 18–24 h) then inspect well‑isolated colonies with naked eye and magnifiers.
- Tilt plate for elevation; use loop/needle to test texture.
Interpretation:
- Systematic observation narrows down possible taxa
- Guides selection of confirmatory biochemical or molecular tests (e.g catalase, coagulase)
Limitations:
- Morphology is influenced by media type and growth conditions so must be controlled and recorded.
- Useful for presumptive ID but not definitive; must be backed by further testing.
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