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Medical Microbiology Lectures
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HOW TO READ A CULTURE PLATEOR
INTERPRETATION OF A CULTURE PLATE
Dr.I.Wani,Centre for Interdisciplinary Biomedical Research
Adesh Institute of Medical Sciences & Research,Bathinda
Obectives: why to interpret?To have a clear idea about pathogen isolatedTo identify it using suitable presumptive &
diagnostic modules used in that particular infection it causes
To study its sensitivity profileTo arrive at most suited treatment
recommended to treat that infection.
IDENTIFICATION METHODSCultural characteristicsStaining reactionSize: in microns(μ )or micro meters(μm)Shape: circular,irregular or rhizoidSurface: smooth,wavy,rough,granular,glistening etc.Elevation: elevated,effuse,convex,concave,umbonate or
umblicateEdge : entire,undulate,crenated,curledColor: colorless,pink,black,red,bluish-greenStructure: opaque,translucent or transparentConsistancy: friable,viscid,butyrous or membranous
CULTURAL CHARACTERISTICS
Examples : Colony characteristics
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
HAEMOLYSIS1.Alpha (α)hemolysis: Partial hemolysis/Greenish
discoloration
2.Beta(β) hemolysis : Complete hemolysis/Colorless
3.Gamma(γ) hemolysis : No hemolysis/no change
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
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
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
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
THANK YOU
…………Have a good day