Introduction to Antimicrobial
Activity: Mechanism and AMR
I.Introduction to Antimicrobial Activity
Definition: Antimicrobial activity refers to the ability of a substance to kill
or inhibit the growth of microorganisms, including bacteria, fungi, viruses,
and parasites. These substances are broadly termed "antimicrobial
agents."
Importance: Antimicrobial agents are crucial in medicine, agriculture, and
public health for preventing and treating infectious diseases, controlling
microbial growth in various environments, and ensuring food safety.
Key Terms:
* Antimicrobial Agent:
Any substance that kills or inhibits the growth of microorganisms.
* Antibiotic:
A specific type of antimicrobial agent that targets bacteria. Traditionally,
antibiotics were substances produced by microorganisms, but many are
now synthetically or semi-synthetically derived.
* Antiseptic:
Antimicrobial agents applied to living tissues (e.g., skin) to reduce the risk
of infection.
* Disinfectant:
Antimicrobial agents applied to inanimate objects or surfaces to kill or
inhibit microorganisms.
* Bactericidal:
Kills bacteria.
* Bacteriostatic:
Inhibits the growth and reproduction of bacteria, allowing the host
immune system to eliminate them.
II. Mechanisms of Antimicrobial Action
, Antimicrobial agents exert their effects by targeting essential cellular
processes or structures unique to microorganisms, minimizing harm to
host cells. The main mechanisms include:
Inhibition of Cell Wall Synthesis:
* Targets the peptidoglycan layer, which is unique to bacteria.
* Examples: Beta-lactam antibiotics (Penicillins, Cephalosporins,
Carbapenems, Monobactams) interfere with transpeptidases (Penicillin-
Binding Proteins - PBPs) responsible for cross-linking peptidoglycan chains,
leading to a weak cell wall and osmotic lysis. Glycopeptides (Vancomycin)
bind to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing
their incorporation into the cell wall.
Disruption of Cell Membrane Integrity:
* Targets the microbial cell membrane, leading to leakage of intracellular
components and loss of cellular homeostasis.
* Examples: Polymyxins (e.g., Colistin) act as cationic detergents, binding
to and disrupting the outer and inner membranes of Gram-negative
bacteria. Lipopeptides (Daptomycin) insert into the bacterial membrane,
causing depolarization and inhibition of protein, DNA, and RNA synthesis.
Inhibition of Protein Synthesis:
* Targets bacterial ribosomes (70S), which are structurally different from
eukaryotic ribosomes (80S).
* Examples:
* Aminoglycosides (Streptomycin, Gentamicin) bind to the 30S
ribosomal subunit, causing misreading of mRNA and premature
termination of protein synthesis.
* Tetracyclines (Doxycycline) bind to the 30S ribosomal subunit,
preventing the binding of aminoacyl-tRNA.
* Macrolides (Erythromycin, Azithromycin), Lincosamides
(Clindamycin), and Chloramphenicol bind to the 50S ribosomal subunit,
inhibiting peptide bond formation and translocation.
Inhibition of Nucleic Acid Synthesis:
* Targets enzymes involved in DNA replication or RNA transcription.
* Examples:
Activity: Mechanism and AMR
I.Introduction to Antimicrobial Activity
Definition: Antimicrobial activity refers to the ability of a substance to kill
or inhibit the growth of microorganisms, including bacteria, fungi, viruses,
and parasites. These substances are broadly termed "antimicrobial
agents."
Importance: Antimicrobial agents are crucial in medicine, agriculture, and
public health for preventing and treating infectious diseases, controlling
microbial growth in various environments, and ensuring food safety.
Key Terms:
* Antimicrobial Agent:
Any substance that kills or inhibits the growth of microorganisms.
* Antibiotic:
A specific type of antimicrobial agent that targets bacteria. Traditionally,
antibiotics were substances produced by microorganisms, but many are
now synthetically or semi-synthetically derived.
* Antiseptic:
Antimicrobial agents applied to living tissues (e.g., skin) to reduce the risk
of infection.
* Disinfectant:
Antimicrobial agents applied to inanimate objects or surfaces to kill or
inhibit microorganisms.
* Bactericidal:
Kills bacteria.
* Bacteriostatic:
Inhibits the growth and reproduction of bacteria, allowing the host
immune system to eliminate them.
II. Mechanisms of Antimicrobial Action
, Antimicrobial agents exert their effects by targeting essential cellular
processes or structures unique to microorganisms, minimizing harm to
host cells. The main mechanisms include:
Inhibition of Cell Wall Synthesis:
* Targets the peptidoglycan layer, which is unique to bacteria.
* Examples: Beta-lactam antibiotics (Penicillins, Cephalosporins,
Carbapenems, Monobactams) interfere with transpeptidases (Penicillin-
Binding Proteins - PBPs) responsible for cross-linking peptidoglycan chains,
leading to a weak cell wall and osmotic lysis. Glycopeptides (Vancomycin)
bind to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing
their incorporation into the cell wall.
Disruption of Cell Membrane Integrity:
* Targets the microbial cell membrane, leading to leakage of intracellular
components and loss of cellular homeostasis.
* Examples: Polymyxins (e.g., Colistin) act as cationic detergents, binding
to and disrupting the outer and inner membranes of Gram-negative
bacteria. Lipopeptides (Daptomycin) insert into the bacterial membrane,
causing depolarization and inhibition of protein, DNA, and RNA synthesis.
Inhibition of Protein Synthesis:
* Targets bacterial ribosomes (70S), which are structurally different from
eukaryotic ribosomes (80S).
* Examples:
* Aminoglycosides (Streptomycin, Gentamicin) bind to the 30S
ribosomal subunit, causing misreading of mRNA and premature
termination of protein synthesis.
* Tetracyclines (Doxycycline) bind to the 30S ribosomal subunit,
preventing the binding of aminoacyl-tRNA.
* Macrolides (Erythromycin, Azithromycin), Lincosamides
(Clindamycin), and Chloramphenicol bind to the 50S ribosomal subunit,
inhibiting peptide bond formation and translocation.
Inhibition of Nucleic Acid Synthesis:
* Targets enzymes involved in DNA replication or RNA transcription.
* Examples:
