Laboratory Diagnosis of Infectious Disease

The Complexity of Bacterial Ecology

Stains – necessary because of bacterial motion and lack of optical contrast

Laboratory Identification of Common Strains of Bacteria

Basic Principles of Laboratory Diagnosis

Five Ways a Lab Can Diagnose an Infectious Disease

If you see...

It is probably...



mononuclear cells

viral, mycobacterial, fungal, or other nonbacterial


helminthic infestation (parasitic)


mycobacterial or fungal

obliterative endarteritis


mixed granulomatous, suppurative, and lymphoid hyperplastic changes

cat-scratch disease

stellate abscesses

lymphogranuloma venereum

Use This Stain…

To Test For…

A Positive Result is Indicated If…

Gram stain

most bacteria, some yeast

cells are blue (gram+) or pink (gram-)

Acid-Fast Stain (Kinyoun)

all mycobacteria, also Candida, Nocardia and the Pittsburgh Agent (Legionella micdadei)

cells are pink (also beaded, curved)

Auramine-rhodamine Stain


fluorescence is observed

India Ink Preparation

cryptococci in CSF

ink is excluded from large capsules

KOH Preparation

elastin (indicates necrotizing pneumonia), fungi

elastin/fungi observed (don’t dissolve)

Tzanck’s Preparation

herpesviruses (zoster or simplex)

multinucleated giant cells observed

Silver Stain

fungi and pneumocystitis carinii

stain is absorbed

For This Disease

Use This Assay

Which Will Detect These Agents


Latex agglutination

Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitis, Cryptococcus neofermans

Respiratory Tract


Bordetella pertussis, legionella disease, infection influenza virus, respiratory syncytial virus, adenovirus

Genitourinary tract

Enzyme Immunoassay

Chlamydia species, herpes simplex infection virus 1 and 2

Hepatitis B


Hepatitis B surface antigen

Human immunodeficiency virus (HIV) infection (HIV) infection

Enzyme immunoassay

HIV p24 core antigen


Identification of Bacterial Organism


Laboratory Tests for Drug Resistance