HomeBIOL 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

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

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:

Number of Colonies

Dilution

Volume plated

CFU/mL=Dilution×Volume platedNumber of Colonies

Example:

50 colonies
0.1 mL plated
10⁻⁴ dilution

−

0.1

CFU/mL=10−4×0.150

CFU/mL=5×106

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.

Purpose:

Neutralize pathogens
Tag microbes for destruction

IgM vs IgG

IgM

First antibody produced
Indicates recent or acute infection
Large molecule (pentamer)

IgG

Most abundant antibody
Appears later in infection
Provides long-term immunity
Can cross the placenta

Body Defenses Against Infection

First Line of Defense (Physical Barriers)

Skin
Mucous membranes
Tears
Saliva
Stomach acid

Second Line of Defense (Innate Immunity)

Phagocytes (macrophages, neutrophils)
Inflammation
Fever
Complement system

Third Line of Defense (Adaptive Immunity)

B cells → antibodies
T cells → kill infected cells
Memory cells → faster response in future infections