MLAB 2434 – MICROBIOLOGYKERI BROPHY-MARTINEZ
Use of Colony Morphology for Presumptive ID of Microorganism
Importance of Colonial Morphology as a Diagnostic Tool
Provide a presumptive diagnosis in times of critical need Best guess giving type of specimen and what is seen
before confirmatory tests Help jump-start therapy
Enhance quality of patient care through rapid results and cost effectiveness Prevents time-consuming testing that yields few
results Play a significant role in quality control
Helps maintain accuracy of commercial or automated systems
Troubleshoot mixed cultures or errors in commercial systems
Colony Morphology (cont’d)
Initial Observation & Interpretation of Cultures“Read” routine cultures after 18
to 24 hours of incubation If cultures cannot be read after
24 hours, refrigerate to prevent overgrowth and drying
Colony Morphology (cont’d)
Compare growth on different media
Examples:• If good growth on BAP but no growth
on MAC, the bacteria is probably a gram positive organism
• If MAC growth is pink, the organism is a lactose fermenter
Fermenting vs. Non-Fermenting
Colony Morphology (cont’d)
Gross Colony CharacteristicsHemolysis on BAP (Chocolate
agar does not show true hemolysis)• α hemolysis
• green discoloration on the media• Due to partial lysing of the RBC’s
Colony Morphology (cont’d)
β hemolysis – complete clearing of blood around colonies on BAP
Colony Morphology (cont’d)
Gamma hemolysis Absence of
hemolysis, nonhemolytic
Colony Morphology (cont’d)
Size ( large, medium, small, pinpoint)
Margin or edge (smooth, filamentous)
Elevation ( raised, convex, flat)Density( transparent, translucent,
opaque)Consistency (brittle, creamy, dry)Pigment (production of color)Odor (fruity, old sock)
Colony Morphology (cont’d)
Shape, edge and elevation of bacterial colonies
Liquid Media Environment
Growth of Organisms in Liquid Media
Streamers or vines are associated with certain streps
Puff balls associated with streps
Growth of Organisms in Liquid Media Turbidity
Cloudiness of the medium
Often see gas
References
Engelkirk, P., & Duben-Engelkirk, J. (2008). Laboratory Diagnosis of Infectious Diseases: Essentials of Diagnostic Microbiology . Baltimore, MD: Lippincott Williams and Wilkins.
Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.