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COLONY MORPHOLOGY AND ARRANGEMENT OF BACTERIAL CELLS.pptx
- 1. COLONY MORPHOLOGY AND ARRANGEMENTOF BACTERIAL CELLS SRUTHI R
- 2. • Bacteria growon solid media as colonies. A colony is defined as a visible mass of microorganisms all originating from a single mother cell, therefore a colony constitutes a clone of bacteria all genetically alike. • In the identification of bacteria and fungi much weight is placed on how the organism grows in or on media.
- 3. NUTRIENT MEDIUM • Imaginebacteria are like tiny living creatures that need food to live, grow, and reproduce just like us. But they are microscopic and can’t eat like us, right? • So, we give them their food in a special form like a soft jelly or liquid soup that contains all the nutrients they love this is what we call a culture medium. DEFINITION OF CULTURE MEDIUM A nutrient medium (or culture medium) is: “A substance (solid, liquid, or semi-solid) that contains nutrients that allow microorganisms (like bacteria) to grow in the lab.”
- 4. Similarly, for bacteria,we prepare a bacterial formula that includes: • Sugars (energy) • Proteins/amino acids (building blocks) • Minerals (for enzymes) • Water (life support) Type Appearance Examples Usage Liquid Media Broth (like soup) Nutrient Broth Growing many bacteria in bulk Solid Media Jelly-like surface Nutrient Agar, Blood Agar Growing isolated colonies Semi-solid Media Soft jelly Motility Agar Testing movement (motility)
- 5. AGAR – SOLIDMEDIA • Agar is a jelly-like substance extracted from red algae. • It solidifies at 40–45°C, but doesn’t melt until 90–100°C. • Bacteria can’t digest agar, so it’s perfect to keep it solid.
- 6. WHATS INDISE THEAGAR??? • NUTRIENT AGAR COMPOSITION Component Function Peptone Provides amino acids/proteins Beef Extract/Yeast Extract Vitamins, minerals, growth factors Sodium Chloride (NaCl) Maintains osmotic balance Distilled Water Solvent, life support Agar Solidifying agent Osmotic balance, also known as osmoregulation, refers to the process by which organisms maintain the appropriate balance of water and electrolytes (salts) in their body fluids.
- 8. COLONY SIZE Colony sizerefers to the diameter of a single, isolated bacterial colony that forms on a solid agar medium after incubation. • It gives an idea of how fast and extensively the bacteria grow. • Colony size is usually measured in: Millimeters (mm)
- 9. Colony Size Approx.Diameter Description Example Organism Reason Pinpoint (PP) <0.5 mm Tiny dots, hard to pick with loop Streptococcus pyogenes Slow growth, small colonies even after 24h Small 0.5–1 mm Easily visible but still small Enterococcus, Neisseria Somewhat fast growers but limited spreading Medium 1–3 mm Clear, round colonies E. coli, Salmonella Moderate growth rate Large >3 mm Big, spreading colonies Bacillus subtilis, Pseudomonas aeruginosa Fast growth, motility, good nutrient usage
- 10. FACTORS DETERMINING THECOLONY SIZE Factor Explanation Nutrient availability Richer media support faster growth and larger colonies. Temperature Optimal temperature allows maximum growth rate (e.g., 37°C for human pathogens). Oxygen levels Aerobes grow faster on surface; anaerobes need special conditions. Incubation time The longer the incubation, the larger the colony (up to a point). Genetic growth rate Some bacteria are naturally slow-growers (e.g., Mycobacterium). Motility Motile bacteria spread more, forming larger, spreading colonies. Water availability Drier media slows growth, limiting size. Antibiotics/toxins Can restrict growth, forming smaller colonies.
- 11. COLOR There are TWOMAIN REASONS a colony looks colored: Pigment Production by the Bacteria • These are natural colors produced by the bacteria themselves. • These pigments may be diffusible (spread into the agar) or non-diffusible (stay in the colony only). Color Changes Caused by Reactions in the Media • If the media contains pH indicators, dyes, or blood, the bacteria can alter the color by their metabolism (acid production, hemolysis, etc.) • These are indirect colors caused by the bacteria's activity, not by pigments.
- 12. Bacterium Pigment ColonyColor Notes Serratia marcescens Prodigiosin Bright Red Temperature-sensitive pigment (seen at 25°C) Micrococcus luteus Carotenoid Yellow Non-motile, Pseudomonas aeruginosa Pyocyanin, Pyoverdine Blue-green Can diffusely color the medium; smells fruity Chromobacterium violaceum Violacein Violet Rare, tropical soil bacteria Staphylococcus aureus Staphyloxanthin Golden yellow Golden glow on nutrient agar Flavobacterium Flexirubin pigment Yellow-orange Soil and water bacteria Rhodococcus Carotenoid Spink Grows slowly, often in soil Mycobacterium (some species) Carotenoids Yellow / Orange Slow growing, pigmented or non-pigmented species
- 13. Type What ItMeans Example Diffusible Spreads into the surrounding agar Pseudomonas aeruginosa Non-diffusible Stays within the colony S. aureus, M. luteus Color from Media Reactions Bacterium Medium Colony Color Reason E. coli MacConkey Pink Lactose fermenter (acid turns indicator pink) Salmonella MacConkey Colorless No lactose fermentation S. aureus Nutrient agar Golden yellow Natural pigment M. luteus Nutrient agar Bright yellow Carotenoid P. aeruginosa Nutrient agar Blue-green colony & medium Pyocyanin diffuses S. marcescens Nutrient agar (25°C) Red Prodigiosin pigment Klebsiella MacConkey Mucoid pink Lactose fermenter with capsule S. pyogenes Blood agar Translucent + clear halo Beta-hemolysis Corynebacterium diphtheriae Tellurite agar Black colonies Tellurite reduced to metallic black
- 14. TEXTURE • Just likehuman skin can be oily, dry, rough, soft, bacterial colonies also have different textures when they grow on solid agar plates. • “The surface appearance and feel of a bacterial colony on an agar plate whether it looks smooth, moist, dry, sticky, slimy, brittle, or rough.” It's a visible clue to: • What kind of outer surface the bacteria have • Whether they produce capsules, biofilms, flagella
- 15. HOW DO WEOBSERVE TEXTURE? • Texture is assessed by: • Visual inspection – shine a light at an angle to see reflections. • Touching with loop/needle (in sterile condition) – gently touch and lift: • Does it stick to the loop? • Does it break, or drag like mucus (CHEESE IN PIZZA ) Smooth Colony Appearance: Glossy, shiny, round, moist Touch: Soft, spreads easily Cause: Bacteria with regular cell walls, no capsules, or mild surface secretion Example Bacteria Notes E. coli Smooth colonies Staphylococcus aureus Smooth golden-yellow Klebsiella pneumoniae Smooth but may become mucoid
- 16. Dry Colony Appearance: Matte,dull, chalky Touch: Crumbly, powdery, may flake Cause: No capsule, limited moisture production, often Gram-positive rods/spores Example Bacteria Notes Bacillus subtilis Large, dry, rough-edged colonies Mycobacterium tuberculosis Very dry, breadcrumb-like Corynebacterium diphtheriae Dry, gray-black on special media
- 17. Mucoid Colony Appearance: Verywet, shiny, like mucus Touch: Sticky when touched with loop Cause: High capsule or exopolysaccharide production Often associated with virulence and biofilm formation Example Bacteria Notes Klebsiella pneumoniae Thick capsule; glassy mucoid appearance Pseudomonas aeruginosa (mucoid strains) Seen in CF patients Haemophilus influenzae Sticky mucoid colonies Important Clinical Point: Mucoid colonies = more resistant to phagocytosis and immune attack (GATE)
- 18. Viscid Colony Appearance: Similarto mucoid but slightly thicker, viscous Touch: Pulls into threads or strings when lifted with loop Cause: Partial capsule/slime layer; intermediate between smooth & mucoid Example Bacteria Notes Neisseria meningitidis Sticky, thread-like Klebsiella (less capsule) Semi-viscous variant
- 19. ELEVATION • Tilting theagar plate at eye level under light and noting how the colony lifts off the surface. Flat Colony •Looks like: Level with the surface of the agar, no bulge, spreads out like water. •Edges merge smoothly with agar. •No height at all Example Bacteria Bacillus cereus Streptococcus pyogenes
- 20. Raised Colony •Looks like:Slightly elevated, like a pillow or pancake •Even across the top (no central bump) Example Bacteria Notes Staphylococcus epidermidis White, raised, round colonies E. coli On NA or MacConkey, mildly raised
- 21. • Convex colony Lookslike: Dome-shaped, circular bulge upward — like a water droplet or bubble. Smooth, curved top. Example Bacteria Notes Staphylococcus aureus Convex, golden colonies Micrococcus luteus Smooth, yellow, convex
- 22. • Umbonate Colony Middlerises more than the edges Example Bacteria Notes Bacillus subtilis Classic umbonate colony Some Mycobacterium spp. Umbonate • Crateriform Colony Looks like: Raised edges with a depressed center Like a bowl Example Bacteria Notes Staphylococcus epidermidis (some strains) Crateriform, especially older colonies Mycobacterium smegmatis Can form this on specific media
- 23. • Draughtsman Colony(Target-Shaped) Alternating elevation zones – very unique Example Bacteria Notes Streptococcus pneumoniae Draughtsman-like colonies after 24–48 hrs due to autolysis Requires CO₂ incubation Causes colony center to collapse Indicates: Autolysis at center → death of older cells in middle Highly diagnostic for S. pneumoniae
- 24. FORM • "What shapedoes the colony take when seen from the top?“ Round (Circular) Colony Description: • Smooth, perfectly circular colony • Uniform growth in all directions • Edges are even Visualize: Like a drop of water or coin Example Bacteria Notes E. coli On nutrient agar, shows moist, round colonies Staphylococcus aureus Golden yellow, circular Micrococcus luteus Circular, yellow colonies
- 25. Irregular Colony Description: • Unevenor wavy outline • Growth is asymmetrical • Edges are distorted, not uniform Example Bacteria Notes Bacillus subtilis Large, dry, irregular colonies Proteus vulgaris Irregular form
- 26. • Filamentous Colony Description: •Central body with long, thin, hair-like projections • Radiating lines or rays extending outwards • Like the sun with rays Example Bacteria Notes Nocardia spp. Filamentous Streptomyces spp. Filamentous, dry colonies Actinomyces spp. Similar branching appearance Clue: Common in soil bacteria, especially Actinomycetes
- 27. • Rhizoid Colony TheRoot System Description: • Thin, root-like branching from the center • Central colony sends wavy arms into agar • Looks like plant roots or nerves Example Bacteria Notes Bacillus mycoides Famous for rhizoid colonies Clostridium tetani Can show spreading rhizoid form in anaerobic media
- 28. MARGIN • Tilt theagar plate slightly and look from the top view, preferably under light. The edge of the colony often contrasts with the surrounding agar
- 29. • Entire Margin Appearance:Clean margin, edges Example: Staphylococcus aureus • Lobate margin Appearance: Big, wavy lobes like cauliflower petals. Example: Some Bacillus species • Scalloped Margin Appearance: Repeated curves like waves or shell pattern Example- some fungal species
- 30. • Filiform Margin– Hairy or thread-like Appearance: Very thin, fine thread-like projections. Example: Actinomyces or Streptomyces • Undulate Margin – Wavy but smooth Appearance: Gently wavy, not too sharp. Example: Some strains of E. coli • Curled margin– Circular rings inside rings Appearance: Looks like a fingerprint or tree rings. Example: Seen in Mycobacterium colonies sometimes
- 31. • Serrate Margin– Saw-toothed, sharp edges Appearance: Jagged, toothed like a saw or knife. Example: Some Proteus species