38 Questions
What happens when bacteria are resistant to an antimicrobial drug?
Their growth is not halted by the maximal level of the agent.
What is an example of intrinsic resistance?
Mycoplasma, which lacks a cell wall and is resistant to penicillin.
What is acquired resistance?
A mechanism by which bacteria adapt to antibiotics.
What is a result of antibiotic resistance?
Bacteria evolve to evade the effect of antibiotics.
What is an example of a mechanism of antibiotic resistance?
Bacteria changing their structure to resist antibiotics.
What is a characteristic of intrinsic resistance?
It is a natural ability of bacteria to resist antibiotics.
What is a consequence of antibiotic resistance?
The treatment of bacterial infections becomes more challenging.
What is a mechanism by which bacteria acquire resistance?
All of the above.
What is the primary purpose of antibiotics in medical treatment?
To treat bacterial infections
What is the key characteristic of antimicrobial drugs?
Their selective toxicity
What is the significance of carefully controlling the concentration of antimicrobial drugs?
To ensure the microorganism is killed while the host cells are tolerated
What is the relationship between selective toxicity and the effect of antimicrobial drugs?
Selective toxicity allows the drug to kill microorganisms without harming host cells
What is the primary concern in using antimicrobial drugs to treat bacterial infections?
The development of resistance in microorganisms
What is the role of antibiotics in treating bacterial infections?
To kill or inhibit the growth of microorganisms
What is the significance of relative selective toxicity in antimicrobial drugs?
It requires careful control of the drug concentration
What is the major limitation of antimicrobial drugs in treating bacterial infections?
Their selective toxicity is relative, not absolute
What is the fundamental characteristic of antibiotic resistance?
A property of the microbe itself
What is the primary mechanism by which bacteria can acquire resistance to antibiotics?
Acquiring DNA from a bacterium that is already resistant
What is an example of a bacterium that has developed resistance to an antibiotic?
Mycobacterium tuberculosis resistant to rifamycin
What is the result of spontaneous mutations in DNA that can lead to antibiotic resistance?
Insertion, deletion, or substitution of one or more nucleotides within the genome
What is the term for the transfer of genetic material from one bacterium to another?
Horizontal gene transfer
What is the consequence of using a single antibiotic to treat an infection?
The development of antibiotic resistance
What is the primary mechanism of DNA transfer from one bacterium to another?
All of the above
What is the primary function of enzymes involved in antibiotic resistance?
Destroying or inactivating the antimicrobial agent
Which of the following is an example of modified target sites in antibiotic resistance?
S. pneumoniae resistance to B-lactam drugs
What is the primary function of efflux pumps in antibiotic resistance?
Decreasing accumulation of the drug
What is the result of alterations in the major bacterial penicillin binding proteins in S. pneumoniae?
Decreased binding of the antibiotic to its target
What is the primary mechanism of antibiotic resistance in gram-negative bacteria?
Decreased accumulation of the drug through alteration of porins
Where are the genes encoding efflux pumps typically located?
On both chromosomes and plasmids
What is the characteristic of drug efflux pumps in multidrug-resistant cells?
Broad substrate specificity
What is the function of B-lactamase enzymes?
To hydrolytically inactivate the B-lactam ring of penicillins and cephalosporins
What is the characteristic of TEM-1 B-lactamase?
It is plasmid-encoded
What is the function of acetyltransferases?
To transfer an acetyl group to the antibiotic
What is the function of esterases?
To hydrolyse the lactone ring of macrolides
What is the characteristic of AmpC B-lactamase?
It is chromosomally encoded and inducible
What is the consequence of KPC B-lactamase production?
Resistance to all B-lactams including carbapenems
What is the characteristic of bacteria that express KPC B-lactamase?
They often encode resistance to other antibiotic classes
What is the difference between TEM-1 and AmpC B-lactamases?
TEM-1 is plasmid-encoded, while AmpC is chromosomally encoded
Study Notes
Antibiotics and Bacterial Infections
- Antibiotics are effective against bacterial infections due to their selective toxicity, which allows them to kill or inhibit microorganism growth without harming the host cells.
Bacterial Resistance to Antibiotics
- Bacterial resistance occurs when bacteria evolve to evade the effect of antibiotics through multiple mechanisms.
- Resistance can be intrinsic or acquired.
- Intrinsic resistance: bacteria survive antibiotics due to their inherent structure or components, e.g., mycoplasma lacks a cell wall, making it resistant to penicillin.
Acquired Resistance
- Bacteria acquire resistance through new genetic mutations or by getting DNA from a resistant bacterium.
- Example: Mycobacterium tuberculosis resistance to rifamycin.
Mechanisms of Antibiotic Resistance
- Genetic alterations:
- Spontaneous mutations in DNA, e.g., chromosomal alteration by insertion, deletion, or substitution of nucleotides.
- DNA transfer from one bacterium to another, often encoded in extrachromosomal plasmids.
- Altered expression of protein in drug-resistant organisms:
- Modification of target sites, e.g., S. pneumoniae resistance to β-lactam drugs involves alterations in penicillin binding proteins.
- Decreased accumulation of the drug, e.g., gram-negative bacteria altering porins in their outer membrane.
- Expression of efflux pumps, responsible for decreased drug accumulation in multidrug-resistant cells.
- Enzymatic activation:
- Antibiotic-inactivating enzymes, e.g., β-lactamase, acetyltransferases, and esterases.
- Examples of β-lactamase include TEM-1, AmpC, extended spectrum β-lactamase (ESBL), and Klebsiella pneumoniae carbapenemase (KPC).
Antibiotics are used to treat bacterial infections. Antimicrobial drugs are effective in treating infections due to their selective properties.
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