Textbook Question
While hiking, Huda wants to ensure that the river water is clean enough to drink and will not cause any intestinal infections. How could she treat water from a stream so that it is safe to drink?
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Ch. 7 - Fundamentals of Microbial Growth
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619
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Table of contents
- Ch. 1 - Introduction to Microbiology22
- Ch. 2 - Biochemistry Basics19
- Ch. 3 - Introduction to Prokaryotic Cells17
- Ch. 4 - Introduction to Eukaryotic Cells16
- Ch. 5 - Genetics25
- Ch. 6 - Viruses and Prions12
- Ch. 7 - Fundamentals of Microbial Growth20
- Ch. 8 - Microbial Metabolism16
- Ch. 9 - Principles of Infectious Disease and Epidemiology11
- Ch. 10 - Host Microbe Interactions and Pathogenesis19
- Ch. 11 - Innate Immunity24
- Ch. 12 - Adaptive Immunity22
- Ch. 13 - Immune System Disorders15
- Ch. 14 - Biomedical Applications: Vaccines, Diagnostics, Therapeutics, and Molecular Method14
- Ch. 15 - Antimicrobial Drugs18
- Ch. 16 - Respiratory System Infections16
- Ch. 17 - Skin and Eye Infections19
- Ch. 18 - Nervous System Infections12
- Ch. 19 - Digestive System Infections20
- Ch. 20 - Urinary and Reproductive System Infections10
- Ch. 21 - Cardiovascular and Lymphatic Infections15
Norman-McKay2nd EditionMicrobiology: Basic and Clinical PrinciplesISBN: 9780137661619Not the one you use?Change textbook
Chapter 7, Problem 19
A bacterial specimen exhibits the following growth on blood agar. What can you most reasonably conclude about the bacterium? Select all that apply.
a. It is not S. pyogenes.
b. It is alpha hemolytic.
c. It is beta hemolytic.
d. It is gamma hemolytic.
e. It is Gram-positive.
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Verified step by step guidance1
Step 1: Understand the types of hemolysis on blood agar. Blood agar is used to differentiate bacteria based on their ability to lyse red blood cells, producing three types of hemolysis: alpha (partial hemolysis, greenish discoloration), beta (complete hemolysis, clear zone), and gamma (no hemolysis, no change).
Step 2: Identify the hemolysis pattern shown by the bacterial specimen on the blood agar plate. This is crucial because it helps narrow down the bacterial species or group.
Step 3: Recall that Streptococcus pyogenes is typically beta hemolytic, meaning it produces a clear zone of complete hemolysis around colonies on blood agar.
Step 4: Use the hemolysis pattern observed to determine which options are reasonable. For example, if the specimen shows beta hemolysis, then it could be S. pyogenes and is beta hemolytic; if alpha hemolysis is observed, it is not S. pyogenes but could be other Streptococcus species like S. pneumoniae.
Step 5: Consider Gram staining characteristics. Most hemolytic streptococci are Gram-positive cocci, so if the specimen is a streptococcus, it is likely Gram-positive. This helps decide if option (e) is reasonable.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hemolysis Types on Blood Agar
Hemolysis refers to the breakdown of red blood cells around bacterial colonies on blood agar. Alpha hemolysis causes partial, greenish discoloration; beta hemolysis results in clear, complete lysis; gamma hemolysis indicates no hemolysis or change. Identifying hemolysis type helps differentiate bacterial species.
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Introduction to the Types of Culture Media
Characteristics of Streptococcus pyogenes
Streptococcus pyogenes is a Gram-positive bacterium known for beta hemolysis on blood agar, producing clear zones around colonies. Recognizing its hemolytic pattern is key to distinguishing it from other streptococci and related bacteria.
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Gram Staining and Bacterial Classification
Gram staining differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall structure. This classification aids in identifying bacteria and predicting their behavior, including antibiotic susceptibility and pathogenicity.
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Related Practice
Textbook Question
You are collecting a sample from a deep wound for analysis by the clinical microbiology lab. Which of the following is not a consideration as you undertake this process?
a. Avoiding the skin as the wound is swabbed
b. Using an anaerobic culture tube
c. Disinfecting the tube before collecting the sample
d. Washing your hands before and after sample collection
e. Using complex media
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Textbook Question
The _____________ is the time needed to kill 90 percent of a given microbial population at a set temperature. The _____________ is the lowest temperature needed to kill all microbes in a sample within 10 minutes.
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Textbook Question
Which of the following is (are) true? Select all that apply.
a. Scalpels are critical equipment.
b. Endoscopes are noncritical equipment.
c. Stethoscopes are noncritical equipment.
d. Anesthesia tubing is semicritical equipment.
e. Critical equipment contacts intact skin.
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