Small Colony Variants: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes
Small Colony Variants on CLED agar
Introduction
Table of Contents
Small Colony Variants (SCVs) are a subpopulation of bacteria that grow slowly and form unusually small colonies on culture media. They are most commonly described in Staphylococcus aureus, but also occur in Pseudomonas aeruginosa, Escherichia coli, and Listeria monocytogenes. SCVs are associated with chronic, recurrent, and persistent infections due to their altered metabolism and ability to evade host immunity and antibiotics.
Fig. Small Colony Variants of Staphylococcus saprophyticus on CLED agar
Do the above colonies of bacteria, S. saprophyticus, show Small Colony Variants (SCVs)? Yes. Here is why:
S. No
Features
Observation
SCV Indicator?
1.
Colony size
Some colonies are significantly smaller
Yes
2.
Growth medium
CLED supports E. coli, Staphylococcus, Enterococcus, Klebsiella, etc.
SCVs can form here
3.
Color
Yellow colonies suggest lactose fermentation
Color alone doesn’t rule out SCVs
4.
Heterogeneous population
Both large and very small colonies
Characteristic of mixed SCV and wild-type
Morphology
Colonies are pinpoint-sized, non-pigmented, and often non-hemolytic
Grow more slowly than typical strains
May require supplementation (e.g., hemin, menadione, thymidine) depending on auxotrophy
Under microscope: no distinct morphological difference from wild-type strains