BIOL 3150 – Microbiology for the Healthcare Professions Midterm Study Guide Explanation 1. Contamination Purpose of Disinfecting Surfaces Disinfecting surfaces is important to: Kill or reduce microorganisms on surfaces Prevent cross-contamination between patients, samples, and healthcare workers Reduce spread of infectious disease Maintain a sterile working environment Common disinfectants include alcohol, bleach, and hospital-grade disinfectants. Why Hand Washing is Important Hand washing: Removes transient microorganisms Prevents transmission of pathogens Protects both healthcare workers and patients Reduces healthcare-associated infections (HAIs) Proper handwashing typically includes: Wet hands Apply soap Scrub at least 20 seconds Rinse Dry with clean towel 2. Specimen Collection Sterile Containers vs Nonsterile Containers Sterile containers Free from microorganisms Used when contamination must be prevented Examples: Blood cultures Urine cultures Wound cultures Nonsterile containers Used when normal microbes are already present Examples: Stool samples Sputum samples (sometimes) Information Needed When Labeling a Specimen Proper labeling prevents errors. Required information usually includes: Patient name Patient ID number Date and time of collection Type/source of specimen Collector’s initials Physician or test ordered Transport Media Transport media keeps microorganisms alive during transport to the laboratory. Purpose: Prevents organisms from drying out Prevents overgrowth of contaminants Maintains viability of pathogens Example: swabs placed in transport tubes. Why Specimen Storage Requirements Matter Improper storage can: Kill pathogens Allow contaminating organisms to grow Give false results Examples: Some samples require refrigeration Some must be processed immediately Some must be kept at room temperature When a Specimen Should Be Rejected Common reasons: Improper labeling Leaking container Contaminated sample Wrong container Sample stored improperly Sample received too late Insufficient quantity 3. Media Nonselective Media Supports growth of many different organisms. Example: Nutrient agar Blood agar Purpose: Grow a wide range of bacteria. Selective Media Contains substances that inhibit some organisms but allow others to grow. Example: MacConkey agar (selects for Gram-negative bacteria) Differential Media Distinguishes organisms based on metabolic or biochemical characteristics. Example: MacConkey agar differentiates lactose fermenters vs non-fermenters Colonies change color depending on reaction. 4. Staining Simple Stain Uses one dye to visualize bacteria. Purpose: Observe shape Observe arrangement Example stains: Methylene blue Crystal violet Differential Stain Uses multiple dyes to distinguish between types of bacteria. Example: Gram stain Acid-fast stain Gram Stain Steps and Purpose 1. Crystal Violet (Primary Stain) Stains all cells purple 2. Iodine (Mordant) Forms a complex with crystal violet Helps dye stick to cell walls 3. Alcohol or Acetone (Decolorizer) Removes stain from Gram-negative cells Gram-positive cells retain stain 4. Safranin (Counterstain) Stains Gram-negative cells pink/red Gram Positive vs Gram Negative Gram Positive Bacteria Cell wall: Thick peptidoglycan layer Retains crystal violet Color after stain: Purple Gram Negative Bacteria Cell wall: Thin peptidoglycan Outer membrane present Color after stain: Pink/red 5. Streaking for Isolation (4 Quadrant Method) Purpose To separate individual bacterial cells so they grow into isolated colonies. This allows identification of pure cultures. Steps in Clinical Lab Sterilize loop in flame Obtain bacteria from sample Streak first quadrant Flame loop again Drag bacteria from first quadrant into second Repeat for quadrants 3 and 4 Incubate plate Each quadrant dilutes the bacteria, producing isolated colonies. 6. Streaking for Quantification Purpose To estimate the number of bacteria in a sample. Measured as: CFU = Colony Forming Units Each colony represents one viable bacterium (or group). CFU Calculation Example Formula: C F U / m L = Number of Colonies Dilution × Volume plated CFU/mL= Dilution×Volume plated Number of Colonies ​ Example: 50 colonies 0.1 mL plated 10⁻⁴ dilution C F U / m L = 50 10 − 4 × 0.1 CFU/mL= 10 −4 ×0.1 50 ​ C F U / m L = 5 × 10 6 CFU/mL=5×10 6 7. Immunology Antigen An antigen is a substance that triggers an immune response. Examples: Bacteria Viruses Toxins Foreign proteins Antibody An antibody is a protein produced by B cells that specifically binds to an antigen

Contamination

The presence of unwanted microorganisms on surfaces or in specimens.

Disinfection

The process of killing or reducing harmful microorganisms on surfaces.

Transient Microorganisms

Microbes that are temporarily present on the skin and can be removed through hand washing.

Healthcare-associated infections (HAIs)

Infections that patients acquire while receiving treatment for medical or surgical conditions.

Sterile Containers

Containers that are free from any microorganisms, used to prevent contamination.

Transport Media

Substances that keep microorganisms alive during transport to laboratories.

Selective Media

Media that inhibits some organisms but allows others to grow.

Differential Media

Media that distinguishes organisms based on their metabolic or biochemical properties.

Gram Positive Bacteria

Bacteria with a thick peptidoglycan layer in their cell wall that retain the crystal violet stain.

Gram Negative Bacteria

Bacteria with a thin peptidoglycan layer and an outer membrane that do not retain the crystal violet stain.

Streaking for Isolation

A technique used to separate individual bacterial cells to grow isolated colonies.

Colony Forming Units (CFU)

A unit used to estimate the number of viable bacteria in a sample.

Antigen

A substance that triggers an immune response.

Antibody

A protein produced by B cells that specifically binds to an antigen.

IgM

The first antibody produced during an immune response, indicating recent infection.

IgG

The most abundant antibody that provides long-term immunity and can cross the placenta.

Phagocytes

Cells that engulf and destroy pathogens as part of the immune response.

Innate Immunity

The body's first line of defense against infection, including barriers like skin and mucous membranes.

Adaptive Immunity

The immune response that involves B and T cells, providing a targeted response to specific pathogens.