Questions and Answers
What is the primary function of the bacterial capsule in relation to the host's immune system?
What is the main difference between the cell walls of Gram-positive and Gram-negative bacteria?
Which of the following bacteria are more resistant to engulfment by macrophages and PMNs?
Why do chemicals that damage bacterial cell walls not harm the cells of an animal host?
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What is the target of some antimicrobial drugs?
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What is the function of the peptidoglycan in the bacterial cell wall?
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Which of the following structures is not involved in the Gram staining process?
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What is the difference between Gram-positive and Gram-negative bacteria in terms of their cell wall structure?
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What is the primary function of potassium tellurite and bile salt in microbiological culture?
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Which of the following dyes is used to inhibit the growth of Gram-positive and Gram-negative bacteria?
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What is the primary function of sodium chloride in microbiological culture?
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Which of the following is used to decontaminate sputum of other bacteria present in the pulmonary microbiota?
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What is the primary function of bacteriophages in microbiological culture?
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Which of the following is NOT a type of antimicrobial agent?
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What is the primary function of culture media in microbiological culture?
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Which of the following is a method for storing culture media?
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What is a possible way for a microorganism to become pathogenic?
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What is the purpose of a selective culture medium?
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What is a phage?
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Which of the following antimicrobial agents targets Gram-positive bacteria?
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What is the difference between antiseptics and disinfectants?
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What is the primary goal of selective cultivation of microorganisms?
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Which of the following is NOT a type of antimicrobial agent used in selective culture media?
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What can be added to a basic culture medium to make it selective?
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Study Notes
Selective Cultivation of Microorganisms
- Selective culture medium is used to isolate a particular bacterial species or genus
- The medium is composed of a basic medium to which antibiotics, antiseptics, chemicals, dyes, sodium salts, or phages can be added to eliminate unwanted microbial flora
Chemical Substances
- Inhibit certain bacteria
- Examples:
- Potassium tellurite and bile salt inhibit Gram-positive bacteria
- Lithium chloride inhibits Gram-negative bacteria
Dyes
- Used as a colour indicator in a culture medium or as a selective agent against certain bacteria
- Examples:
- Crystal violet (CV) inhibits the growth of Gram-positive bacteria by inducing DNA lesions
- Malachite green inhibits Gram-positive and Gram-negative bacteria
- Methylene blue inhibits Gram-positive bacteria and some yeast by making use of toxic dyes
Sodium Salts
- Known for their inhibitory properties
- Examples:
- Sodium chloride is used to select halophilic (salt-loving) bacteria that resist very high amounts of salts
Phage
- Bacteriophages are specific viruses of bacteria that can infect and even destroy bacteria, in the case of lytic phages
- Examples:
- Used to isolate Mycobacterium tuberculosis by decontaminating the sputum of other bacteria present in the pulmonary microbiota
- T1, T4, and φX174-like phages reduced E. coli population
Antibiotics
- More commonly used selective agents in culture media
- Examples:
- Molecules that target Gram-positive bacteria - penicillin G, bacitracin, vancomycin
- Molecules that target Gram-negative bacteria - colistin, polymixin B
- Molecules that target yeast and fungi - Amphotericin B, cycloheximide, nystatin
Antiseptics
- Rarely used in culture media
- Examples:
- Used to kill microorganisms on the skin
- Disinfectants are used to kill germs on non-living surfaces
Bacterial Anatomy
- Cell wall:
- Both Gram-positive and Gram-negative bacteria possess cell wall peptidoglycans
- Provides mechanical protection and maintains cell shape
- Differentiated by Gram staining characteristics
- Gram-positive bacteria have thicker layers surrounding the plasma membrane
- Target for some antimicrobial drugs
Capsule
- Protects bacteria from:
- Phagocytosis
- Complement activation
- Recognition by phagocytes
- Examples:
- Capsulated Streptococcus pneumoniae resist engulfment by macrophages and PMNs and are virulent
- Non-capsulated strains are easily phagocytosed and are avirulent
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Description
This quiz covers the use of various substances to inhibit bacterial growth, including leave-on products and chemical substances, as well as the use of dyes as selective agents or colour indicators in culture media.