Immunology 3.1 Bacteria and antibiotics 25 Flashcards
(19 cards)
What are the two main types of antibiotics based on their action?
Bacteriostatic and bactericidal
Bacteriostatic antibiotics prevent growth, while bactericidal antibiotics kill bacteria.
Why are antibiotics safe to use in humans?
They affect bacterial metabolism but do not interfere with host cell metabolism
This allows antibiotics to target bacteria without harming the host.
What polymer is present in the bacterial cell wall?
Peptidoglycan (murein)
It consists of polysaccharide molecules cross-linked by amino acid side chains, providing strength and protection.
What surrounds the peptidoglycan layer in Gram negative bacteria?
An outer layer of lipoprotein and lipopolysaccharide
This additional layer contributes to the structural complexity of Gram-negative bacteria.
Why do bacteria become purple or red when Gram stained?
Final colour depends upon the structure of the cell wall and the presence/absence of the lipopolysaccharide outer layer.
It reflects the structural differences between Gram-positive and Gram-negative bacteria.
What is the name of the counterstain in Gram staining?
Safranin
Bacteria stain red with Gram stain. How would you classify them?
Gram negative.
Bacteria stain purple with Gram stain. How would you classify them?
Gram positive.
What is the action of penicillin on bacteria?
It inhibits the formation of cross-linkages in the peptidoglycan cell wall
This weakening leads to cell lysis due to osmotic changes.
Why is penicillin more effective against Gram-positive organisms?
Gram positive bacteria do not have an outer lipopolysaccharide layer and so the penicillin reaches the peptidoglycan easily.
Gram-positive bacteria have a simpler cell wall structure that is more susceptible to penicillin.
How does tetracycline affect bacteria?
It inhibits protein synthesis/translation.
Tetracycline acts as a competitive inhibitor on the 30S ribosomal subunit.
Why are viruses not affected by tetracycline?
Due to the absence of metabolic pathways. Viruses do not have ribosomes or carry out translation.
Antibiotics target specific bacterial functions that viruses do not possess.
What does tetracycline bind to?
The second anticodon binding site on the small subunit of 70S ribosomes.
It prevents the binding of tRNA to the ribosome, blocking protein synthesis.
Why are viruses not affected by penicillin?
Viruses do not have cell walls. (viruses have a protein capsid)
Antibiotics target specific bacterial functions that viruses do not possess.
What is a consequence of the overuse of antibiotics?
The spread of antibiotic-resistant strains of bacteria
Overuse leads to the selection of bacteria that can survive despite antibiotic treatment.
What factors contribute to antibiotic resistance in bacteria?
Rapid division, high mutation rate, and selective advantage
Naturally occurring mutations can confer resistance to antibiotics, giving bacteria an edge in antibiotic-rich environments.
What happens to antibiotic-resistant bacteria in the absence of antibiotics?
They no longer have an advantage over non-mutated forms
However, if they cause an infection, they are difficult to control.
What is a broad spectrum antibiotic?
Works on Gram positive and Gram negative bacteria.
What type of antibiotic stops bacteria growing?
Bacteriostatic.
