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.