Diagnostic Immunology and Microbiology Testing Overview

Goal of diagnostic testing

To detect pathogens or immune responses (antigens/antibodies) in patient samples for diagnosis and treatment.

Bacterial cultures growth

On standard media; results in 24-48 hrs.

Viral cultures requirements

Living cells (tissue culture); results take days-weeks.

Fungal cultures characteristics

Slower-growing, need special media; days-weeks.

Serologic testing purpose

Detects specific antibodies in serum.

Qualitative antibody tests

yes/no.

Quantitative antibody tests

measures antibody amount.

Serum titer

The highest dilution still giving a positive antibody result.

Recent/acute infection indication

High IgM levels.

Past infection or immunity indication

High IgG levels.

Antigen detection method

Uses antibodies to detect pathogen antigens (e.g., rapid strep test).

Antigen detection vs. culture

Faster but less sensitive.

Natural immunity

Inborn (e.g., skin, mucous membranes).

Active immunity

Body makes antibodies.

Passive immunity

Antibodies given.

Toxin

Harmful.

Toxoid

Inactivated vaccine form.

Antitoxin

Antibody that neutralizes toxin.

TB skin test measurement

Measures delayed hypersensitivity, not antibody levels.

Goal of the handwashing lab

Evaluate how effective handwashing is at reducing surface microbes.

Types of hand hygiene tested

Plain soap, antibacterial soap, alcohol-based rub.

Purpose of testing before and after handwashing

To compare microbial load.

Colony count meanings

0-10 = few; 11-100 = moderate; 100+ = many.

Deeper flora appearance after washing

Removal of surface flora may expose deeper layers.

Caution with antibacterial soaps

May disrupt microbiome; contribute to resistance.

Key hygiene practices

Hand hygiene, glove use, cleaning protocols.

Fingernails and rings problem

Harbor microbes and interfere with hand hygiene.

Blood draw site preparation

With antiseptic like chlorhexidine.

Site drying purpose

To ensure full antimicrobial effect.

Aerobic & anaerobic bottles use

To detect bacteria with different oxygen needs.

BacT/Alert system detection

Detects CO₂ as a sign of microbial growth.

Gram stain

A method used to classify bacteria based on the characteristics of their cell walls.

Gram-positive bacteria

Bacteria that appear purple due to a thick cell wall.

Gram-negative bacteria

Bacteria that appear red due to a thin cell wall and an outer membrane.

Normal flora in the mouth

Microorganisms that are typically present in the mouth and help distinguish them from pathogens.

Common oral bacteria genera

Includes Streptococci, Neisseria, Staphylococci, and spirochetes.

Squamous cells under microscope

Appear large, flat, irregular with a nucleus.

Blood agar colony types

α = green halo; β = clear zone; γ = no hemolysis.

Advantage of blood agar

Detects hemolysis and supports fastidious microbes.

4-quadrant streaking

A technique that isolates colonies for better identification.

Colony ID traits

Includes shape, size, color, texture, and odor.

Diagnostic odor example

A fruity smell indicates the presence of Pseudomonas.

Endospore formers

Bacteria like Bacillus that can survive tough environments.

High colony counts on sinks/floors

Found due to moist and exposed conditions.

Environmental infections concern

Common in Operating Rooms (ORs), Intensive Care Units (ICUs), and Neonatal Intensive Care Units (NICUs).

Control methods for environmental sources

Includes sterilization, disinfection, filtration, and UV treatment.

Streptococcus traits

Gram-positive, forms chains, and is catalase negative.

Hemolysis types for Streptococcus

α = green; β = clear; γ = none.

Streptolysins

Hemolysins (O & S) that lyse red blood cells (RBCs).

S. pneumoniae diseases

Includes pneumonia, meningitis, and otitis.

S. pyogenes diseases

Causes strep throat, which can lead to scarlet fever and rheumatic fever.

S. agalactiae causes

Responsible for neonatal sepsis and meningitis.

VRE

Vancomycin-resistant Enterococci.

Catalase test: Strep vs. Staph

Strep = negative; Staph = positive.

SF Broth result

Yellow indicates Enterococcus positive.

Bile-Esculin test

Black indicates positive for Group D Strep.

Optochin sensitivity

Inhibits S. pneumoniae.

CAMP test positive result

Arrowhead formation indicates S. agalactiae.

Bacitracin sensitivity

Group A Strep is sensitive to bacitracin.

Staphylococcus habitat

Found on skin, nose, and mucous membranes.

Pathogenic Staph species

Includes S. aureus, which is golden and coagulase positive.

S. epidermidis infections

Causes infections on catheters and implants.

S. saprophyticus causes

Causes urinary tract infections (UTIs) in women.

Catalase test result for Staph

Positive result shows bubbles form.

Coagulase test identifies

Identifies S. aureus with positive result indicating clumping.

Novobiocin sensitivity

S. epidermidis is sensitive; S. saprophyticus is resistant.

MRSA meaning

Methicillin-resistant Staphylococcus aureus.

Most common Staph species

S. epidermidis.