Chemical Agents of Control and Antimicrobial Treatments

Chapter 11 - Chemical Agents of Control

Chemical Groups and Their Modes of Action

Chemical agents are widely used to control microbial growth in the environment. Each group of chemicals has a distinct mode of action, targeting specific cellular components or functions.

• Halogens: Includes chlorine and iodine (e.g., Wescodyne, Betadine). These agents disrupt protein function by oxidizing cellular components, leading to microbial death.

• Phenols: Examples are triclosan, cresols, chlorohexidine, and hexachlorphene. Phenols damage the cell membrane and interfere with protein function, resulting in cell lysis.

• Alcohols: Includes 70% ethyl alcohol, 70% isopropanol, 95% ethanol, and 100% absolute alcohol. Their effectiveness depends on concentration:

  • Dehydrating effect

  • Dissolves cell membrane

  • Denatures proteins

  • Acts as a degerming agent

• Peroxygens: Hydrogen peroxide and benzyl peroxide disrupt protein function and mechanically remove microbes via bubbling.

• Aldehydes: Formaldehyde and glutaraldehyde inactivate proteins by cross-linking their functional groups.

• Gaseous Sterilants: Ethylene oxide and chlorine dioxide target nucleic acids, sterilizing equipment and surfaces.

• Heavy Metals: Silver nitrate, mercurochrome, and merthiolate bind to and inactivate proteins.

• Surfactants: Includes anionic and cationic agents, such as QUATS (dimethyl benzalkonium chloride), octyl, alkyl, and lauryl sulfate. These disrupt the cell membrane and affect protein function and nucleic acids.

• Acids and Bases: Used to alter environmental pH, affecting microbial survival.

Summary Table: Chemical Agents of Control

Chemical Group	Examples	Mode of Action
Halogens	Chlorine, Iodine (Wescodyne, Betadine)	Protein Function
Phenols	Triclosan, Cresols, Chlorohexidine, Hexachlorphene	Cell Membrane, Protein Function
Alcohols	70% Ethyl Alcohol, 70% Isopropanol, 95% Ethanol, 100% Absolute Alcohol	Dehydration, Dissolves Cell Membrane, Denatures Proteins, Degerming
Peroxygens	Hydrogen Peroxide, Benzyl Peroxide	Protein Function, Mechanical Removal
Aldehydes	Formaldehyde, Glutaraldehyde	Protein Function
Gaseous Sterilants	Ethylene Oxide, Chlorine Dioxide	Nucleic Acid
Heavy Metals	Silver Nitrate, Mercurochrome, Merthiolate	Protein Function
Surfactants	QUATS, Anionic/Cationic Agents	Cell Membrane, Protein Function, Nucleic Acid
Acids and Bases	Various	pH Alteration

Example: 70% isopropanol is commonly used as a disinfectant in clinical settings due to its ability to denature proteins and dissolve cell membranes.

Chapter 12 – Antimicrobial Treatments

Antimicrobial Drug Groups and Their Modes of Action

Antimicrobial drugs are used to treat infections by targeting specific microbial structures or metabolic pathways. The mode of action varies by drug group and organism type.

• Penicillins: Includes Penicillin G, Penicillin V, Ampicillin, Amoxicillin, Methicillin. These are cell wall inhibitors, preventing peptidoglycan synthesis and causing cell lysis.

• Cephalosporins: Generations include Cephalexin, cephalothin, cefaclor, cefoxitin, cefuroxime, cefotaxime, ceftriaxone, ceftazidime. Also cell wall inhibitors.

• Aminoglycosides: Streptomycin, gentamicin, neomycin. These inhibit protein synthesis by binding the 30S ribosomal subunit.

• Chloramphenicol: Inhibits protein synthesis by binding the 50S ribosomal subunit.

• Tetracyclines: Tetracycline, doxycycline, methacycline, minocycline. Inhibit protein synthesis at the 30S ribosomal subunit.

• Macrolides: Erythromycin, clarithromycin, azithromycin. Inhibit protein synthesis at the 50S ribosomal subunit.

• Vancomycin: Cell wall inhibitor, used for resistant bacteria.

• Isoniazid: Cell wall inhibitor, especially for Mycobacterium tuberculosis.

• Rifampin: Inhibits RNA polymerase, blocking RNA synthesis.

• Bacitracin: Cell wall inhibitor, often used topically.

• Polymyxin B: Disrupts cell membrane integrity.

• Sulfa Drugs: Sulfonamides, sulfanilamide, sulfamethoxazole, trimethoprim. Inhibit folic acid synthesis, a key metabolic pathway.

• Quinolones (Fluoroquinolones): Ciprofloxacin. Inhibit DNA synthesis by targeting DNA gyrase.

• Synercid: Used for MRSA, inhibits protein synthesis at the 50S subunit.

• Oxazolidinones: Linezolid (Zyvox), used for MRSA, inhibits protein synthesis at the 50S subunit.

Summary Table: Antibacterial Drug Groups

Drug Group	Examples	Mode of Action
Penicillins	Penicillin G, Penicillin V, Ampicillin, Amoxicillin, Methicillin	Cell Wall Inhibitor
Cephalosporins	Cephalexin, Cephalothin, Cefaclor, Cefoxitin, Cefuroxime, Cefotaxime, Ceftriaxone, Ceftazidime	Cell Wall Inhibitor
Aminoglycosides	Streptomycin, Gentamicin, Neomycin	Protein Synthesis Inhibitor (30S)
Chloramphenicol	Chloramphenicol	Protein Synthesis Inhibitor (50S)
Tetracyclines	Tetracycline, Doxycycline, Methacycline, Minocycline	Protein Synthesis Inhibitor (30S)
Macrolides	Erythromycin, Clarithromycin, Azithromycin	Protein Synthesis Inhibitor (50S)
Vancomycin	Vancomycin	Cell Wall Inhibitor
Isoniazid	Isoniazid	Cell Wall Inhibitor
Rifampin	Rifampin, Rifamycin	Nucleic Acid Inhibitor (RNA polymerase)
Bacitracin	Bacitracin	Cell Wall Inhibitor
Polymyxin B	Polymyxin B	Cell Membrane Inhibitor
Sulfa Drugs	Sulfonamides, Sulfanilamide, Sulfamethoxazole, Trimethoprim	Folic Acid Synthesis Inhibitor
Quinolones	Fluoroquinolones, Ciprofloxacin	Nucleic Acid Inhibitor (DNA)
Synercid	Synercid (MRSA)	Protein Synthesis Inhibitor (50S)
Oxazolidinones	Linezolid (Zyvox)	Protein Synthesis Inhibitor (50S)

Antifungal, Antiviral, Antiprotozoal, and Antihelminth Drugs

These drugs target eukaryotic pathogens and viruses. The specific mode of action is not required for exam purposes, but examples are provided for reference.

• Antifungal: Amphotericin B, flucytosine, nystatin, clotrimazole, miconazole, itraconazole.

• Antiviral: Oseltamivir (Tamiflu), zanamivir (Relenza), acyclovir (Zovirax), zidovudine (AZT), remdesivir, saquinavir, indinavir.

• Antiprotozoal: Quinine, chloroquine, hydroxychloroquine, primaquine, metronidazole (Flagyl).

• Antihelminth: Mebendazole, ivermectin.

Example: Triple antibiotic ointment (Neosporin) contains neomycin, bacitracin, and polymyxin B, providing broad-spectrum antibacterial coverage for minor wounds.

Key Terms and Definitions

• Disinfectant: A chemical used to destroy or inhibit the growth of microorganisms on non-living surfaces.

• Antiseptic: A chemical agent applied to living tissue to reduce the risk of infection.

• Antibiotic: A substance produced by microorganisms that inhibits or kills other microbes.

• Cell Wall Inhibitor: A drug that prevents synthesis of peptidoglycan, weakening the bacterial cell wall.

• Protein Synthesis Inhibitor: A drug that blocks translation by interfering with ribosomal function.

• Nucleic Acid Inhibitor: A drug that disrupts DNA or RNA synthesis, preventing replication or transcription.

• Degerming: The mechanical removal of microbes from a surface, often using alcohol or surfactants.

Additional info:

• Most chemical agents are more effective against vegetative cells than spores.

• Alcohols are most effective at 70% concentration because water aids protein denaturation.

• Antimicrobial resistance is a growing concern; drugs like vancomycin and linezolid are reserved for resistant strains.