Antimicrobial Chemotherapy Overview

Choosing the right antimicrobial drug for an infection depends on three key factors: the type of microorganism causing the infection, its susceptibility to various drugs, and the patient's overall health condition.

A direct examination of body fluids, sputum, or stool can quickly identify the type of microorganism causing an infection.

A 'best guess' approach using drugs known to be effective against the identified microbe.

Testing the effectiveness of various antimicrobial drugs against a specific microorganism.

A standardized method that involves placing antibiotic discs containing different drugs onto a plate with a culture of the suspected microorganism. The larger the zone of inhibition (area where bacterial growth is inhibited) around the disc, the more effective the drug is against that microorganism.

A similar method but uses a strip containing a gradient of drug concentrations, allowing the determination of the minimum inhibitory concentration (MIC).

A method that involves diluting antibiotics in a series of tubes containing liquid growth media. The lowest concentration of the drug that inhibits bacterial growth is called the minimum inhibitory concentration (MIC).

The minimum concentration of a drug that inhibits the growth of a microbe.

The ideal outcome of antimicrobial treatment is to eliminate the infectious agent without harming healthy host cells.

The ability of a drug to harm a microbial target while causing minimal or no harm to the host.

Antibiotics are naturally produced antimicrobial substances made by organisms like bacteria (e.g., Streptomyces) and fungi (e.g., Penicillium).

Many antimicrobial drugs target essential microbial processes, such as protein synthesis, cell wall synthesis, or DNA replication.

Drugs that inhibit protein synthesis can be selective because they target specific ribosomes or steps in protein production unique to microbes.

Antimicrobial drugs aim to disrupt essential processes or structures within bacteria, fungi, protozoa, or inhibit virus replication.

Most antimicrobial drugs work by interfering with enzymes crucial for the synthesis or assembly of macromolecules within a microbe.

Antibiotics that kill bacteria directly instead of just inhibiting their growth.

Penicillins and cephalosporins interfere with enzymes involved in the creation and placement of peptidoglycan, a key component of bacterial cell walls.

Antibiotics that block the synthesis of nucleotides, inhibit replication, stop transcription, or inhibit DNA synthesis.

Antibiotics that inhibit translation by reacting with the ribosome-mRNA complex, preventing the synthesis of proteins.

Prokaryotic ribosomes (found in bacteria) are structurally different from eukaryotic ribosomes (found in humans), allowing selective targeting of bacterial ribosomes.

Antibiotics that inhibit the synthesis of folic acid, a vital nutrient needed by bacteria for DNA and RNA production.

A group of antibiotics derived from natural sources like fungi. They are characterized by a thiazolidine ring, a beta-lactam ring, and a variable side chain. These drugs are effective against bacterial infections.

A group of antibiotics that are chemically related to penicillins, but with a different main ring. They have two sites for connecting different molecules, which gives them a broader spectrum of activity against various bacteria.

The process of producing naturally occurring penicillin through the growth of specific microorganisms.

Part of the penicillin molecule responsible for its effectiveness. It can vary, affecting the drug's ability to target different bacterial species.

A key structure present in both penicillins and cephalosporins. It plays a crucial role in their antibacterial action by interfering with bacterial cell wall synthesis.

Antimicrobial drugs that target the cell membrane can damage the membrane, leading to disruption in cellular metabolism or lysis (cell breakdown). This disruption is often lethal to the microbe.

These drugs are designed to specifically target certain types of microbes, taking advantage of differences in the lipids that make up their cell membranes.

Sulfonamides and trimethoprim work by competitively inhibiting the synthesis of folic acid, a crucial molecule for microbial growth. High concentrations of these drugs outcompete the natural substrate for the enzyme involved.

Folic acid is essential for many metabolic reactions in microbes, and blocking its synthesis severely disrupts their metabolism and leads to growth inhibition or death.

The enzyme dihydropteroate synthetase is a key target for sulfonamides, while dihydrofolate reductase is targeted by trimethoprim. These enzymes are essential for the production of tetrahydrofolic acid (THFA).

Broad-spectrum antimicrobials are effective against a wide range of microbes, while narrow-spectrum antimicrobials are only effective against specific types of microbes.

Penicillin antibiotics were initially effective against a wide range of bacteria, but resistance has become a major concern. They are particularly effective against gram-positive bacteria.

Beta-lactamases are enzymes produced by some bacteria that can break down the beta-lactam ring structure of penicillin and other related antibiotics, rendering them ineffective.

Cephalosporins are a class of antibiotics that have a broad spectrum of activity and are resistant to most penicillinases (enzymes that break down penicillin). They are known for causing fewer allergic reactions compared to penicillins. There are four generations of cephalosporins, each with varying effectiveness against different types of bacteria.

Imipenem and Aztreonam belong to a class of antibiotics called beta-lactam antibiotics, known for their effectiveness against a wide range of bacteria. They have unique structures and mechanisms that make them potent antibacterial agents.

Bacitracin, Isoniazid, Vancomycin, and Fosfomycin tromethamine are powerful antibiotics that work by targeting different aspects of bacterial cell wall synthesis.

Aminoglycoside antibiotics are a group of drugs produced by soil-dwelling bacteria. They are known for their broad-spectrum antibacterial activity, which they achieve by interfering with bacterial protein synthesis.

Streptomycin, an aminoglycoside antibiotic, is particularly effective against bacteria causing bubonic plague, tularemia, and tuberculosis. Gentamicin, another aminoglycoside, is less toxic and often preferred for treating infections caused by gram-negative bacteria.

Tetracycline antibiotics are known for their broad-spectrum activity, meaning they can target a wide range of bacteria, including gram-positive and gram-negative rods, cocci, aerobic and anaerobic bacteria, as well as Mycoplasmas, Rickettsias, and Spirochetes. Their mechanism of action involves binding to ribosomes and blocking protein synthesis.