How to read a culture plate

Medical Microbiology Lectures

1. HOW TO READ A CULTURE PLATE OR INTERPRETATION OF A CULTURE PLATE Dr.I.Wani , Centre for Interdisciplinary Biomedical Research Adesh Institute of Medical Sciences & Research,Bathinda

2. Obectives : why to interpret? To have a clear idea about pathogen isolated To identify it using suitable presumptive & diagnostic modules used in that particular infection it causes To study its sensitivity profile To arrive at most suited treatment recommended to treat that infection.

3. IDENTIFICATION METHODS Cultural characteristics Staining reaction Size: in microns( μ )or micro meters( μ m) Shape: circular,irregular or rhizoid Surface: smooth,wavy,rough,granular,glistening etc. Elevation: elevated,effuse,convex,concave,umbonate or umblicate Edge : entire,undulate,crenated,curled Color: colorless,pink,black,red,bluish -green Structure: opaque,translucent or transparent Consistancy : friable,viscid,butyrous or membranous

4. CULTURAL CHARACTERISTICS

5. Examples : Colony characteristics

6. COLONY CHARACTERISTICS OF SOME COMMON PATHOGENS 1.Staphylococcus( Staph.aureus / Staph.pyogenes ) On Nutrient agar: large,pin -head size(2-4 mm), circular,convex,smooth,shiny,entire edge ,opaque & emulsify easily Most strains produce golden yellow to white,orange pigments On Blood Agar : β - Haemolysis On MacConkey agar: Pink colonies

7. HAEMOLYSIS 1.Alpha ( α )hemolysis : Partial hemolysis/Greenish discoloration 2. Beta( β ) hemolysis : Complete hemolysis/Colorless 3. Gamma( γ ) hemolysis : No hemolysis/no change

8. 2.Streptococcus (Streptococcus pyogenes) On Blood agar: Colonies are small, pin-point(0.5-1.0 mm), circular,semi -transparent with an area of clear hemolysis( β - haemolysis ) around them Virulent strains on fresh isolation produce ‘matt’(finely granular)colonies

9. 3.Escherichia coli( E.coli ) On Nutrient agar: Circular(1-3 mm),smooth,greyish-white,moist ,having entire edge with butyrous consistency. Colonies emulsify easily On Blood agar: Some strains show zone of β - hemolysis On MacConkey agar: Pink colonies

10. 4.Salmonella( S.typhii ) Blood agar: Large colonies(2-3 mm), circular, low convex,translucent,smooth & non-hemolytic MacCankoy agar: Colorless Deoxycholate citrate agar: Colonies show black heads Wilson & Blair bismuth sulphite agar: Jet black colonies with metallic sheen

11. 5. Pseudomonas aeruginosa On Blood agar: β -hemolysis On MacConkey agar: Non-lactose fermenting On Nutrient agar: Large,opaque,irregular colonies with butyrous consistency & fruity odor or earthy smell Produces water soluble pigments which diffuse into the medium i . Pyocyanin - bluish green ii. Fluorescein - yellowish green iii. Pyorubin - red iv. Pyomelanin - black

12. THANK YOU …………Have a good day