Microbiology: Bacterial Inhibition and Detection

Questions and Answers

What is the primary function of the bacterial capsule in relation to the host's immune system?

To enhance the activation of complement proteins

To prevent the direct access of lysosome contents with the bacterial cell (correct)

To stimulate the production of antimicrobial peptides

To facilitate the engulfment of bacteria by phagocytes

What is the main difference between the cell walls of Gram-positive and Gram-negative bacteria?

The presence of a capsule

The thickness of the peptidoglycan layers (correct)

The presence of lipopolysaccharides

The type of peptidoglycan

Which of the following bacteria are more resistant to engulfment by macrophages and PMNs?

Gram-negative bacteria

Non-capsulated Strep. pneumoniae

Capsulated Strep. pneumoniae (correct)

Gram-positive bacteria

Why do chemicals that damage bacterial cell walls not harm the cells of an animal host?

Because the bacterial cell wall is made of different chemicals to those in eukaryotic cells Signup and view all the answers

What is the target of some antimicrobial drugs?

Cell wall synthesis Signup and view all the answers

What is the function of the peptidoglycan in the bacterial cell wall?

To provide mechanical protection and maintain the cell shape Signup and view all the answers

Which of the following structures is not involved in the Gram staining process?

Lysosome Signup and view all the answers

What is the difference between Gram-positive and Gram-negative bacteria in terms of their cell wall structure?

Gram-positive bacteria have a thicker peptidoglycan layer Signup and view all the answers

What is the primary function of potassium tellurite and bile salt in microbiological culture?

To inhibit the growth of Gram-positive bacteria Signup and view all the answers

Which of the following dyes is used to inhibit the growth of Gram-positive and Gram-negative bacteria?

Malachite green Signup and view all the answers

What is the primary function of sodium chloride in microbiological culture?

To select halophilic bacteria Signup and view all the answers

Which of the following is used to decontaminate sputum of other bacteria present in the pulmonary microbiota?

Phage lysin Signup and view all the answers

What is the primary function of bacteriophages in microbiological culture?

To infect and destroy bacteria Signup and view all the answers

Which of the following is NOT a type of antimicrobial agent?

Phage Signup and view all the answers

What is the primary function of culture media in microbiological culture?

To support the growth of microorganisms Signup and view all the answers

Which of the following is a method for storing culture media?

Storing both dehydrated and prepared culture media Signup and view all the answers

What is a possible way for a microorganism to become pathogenic?

By acquiring extra virulence factors Signup and view all the answers

What is the purpose of a selective culture medium?

To eliminate unwanted microbial flora Signup and view all the answers

What is a phage?

A virus that infects and replicates within bacteria and archaea Signup and view all the answers

Which of the following antimicrobial agents targets Gram-positive bacteria?

Penicillin G Signup and view all the answers

What is the difference between antiseptics and disinfectants?

Antiseptics are used on skin, while disinfectants are used on surfaces Signup and view all the answers

What is the primary goal of selective cultivation of microorganisms?

To isolate a specific bacterial species Signup and view all the answers

Which of the following is NOT a type of antimicrobial agent used in selective culture media?

Vitamins Signup and view all the answers

What can be added to a basic culture medium to make it selective?

Antibiotics, antiseptics, chemicals, dyes, and phages Signup and view all the answers

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.