Chemical Control of Microbial Growth and Chemotherapy

Flashcards covering chemical methods of microbial control, including disinfectants, antiseptics, and antibiotics, as well as mechanisms of drug resistance and modes of action.

Chemical Control

Chemicals used to control growth on living tissue and inanimate objects. Most disinfectants merely reduce the population or remove vegetative cells, but do not sterilize.

Factors Affecting Chemical Control

Nature of the material being disinfected, presence of organic materials, pH, contact of disinfectant with microbes. May need to pre-clean area before disinfecting and may need a long contact time for effectiveness.

Disk Diffusion Test

Spread a plate with bacteria, place filter disks soaked in different disinfectants on top, incubate, determine where lawn grows. Extent of the zone of inhibition is correlated with the ability of the disinfectant to inhibit or kill.

Use-Dilution Test

Metal cylinders are dipped in broth cultures of specific test bacteria and then dried. Contaminated cylinders are exposed to disinfectant for desired times. Cylinders are dropped back into broth and growth or no growth is recorded.

Phenolics

Damage cell membranes, damage mycobacterial cell wall (lipid-rich), denature proteins. More effective and less irritating than phenol. Excellent disinfectants for surfaces due to persistence.

Bisphenols

Two phenols bridged together. Denature enzyme needed to make membrane lipids. Work against gram+, gram-, fungi. Pseudomonas are resistant.

Bisbiguanides

Cause gross permeability changes to cell membrane, affects enzymes of aerobic respiration, also blocks enzyme needed for lipid synthesis. Used on skin-mucous membranes.

Halogens

Iodine impairs protein synthesis and alters cell membranes. Chlorine forms hypochlorous acid (HOCl) in water and is a strong oxidizing agent, affecting many enzymes.

Alcohols

Antiseptic and disinfectant. Disrupt membranes (lipids are soluble in alcohols) and proteins denature in alcohols. Kill bacteria and fungi, but not endospores or non-enveloped viruses. Primarily for degerming.

Heavy Metals

Combine with sulfhydryl groups in proteins, denaturing or inhibiting enzyme activity. Includes silver, mercury, copper, nickel, zinc.

Alkylating Agents

Effectively inactivate proteins and nucleic acids. Formaldehyde is an excellent disinfectant, but irritating, mutagen and suspected carcinogen. Glutaraldehyde is a chemical sterilizing agent that disinfects hospital equipment.

Surface-active agents (Surfactants)

Soaps are natural and deformerout willcrobes lipid products emulsifying oily film on skin, which can be washed off. Detergents are synthetic and 1 leave leave no kills microbe. Quats are cationic detergents that disrupt plasma membranes by insertion.

Chemical Food Preservatives

Sulfur dioxide is used in wine making. Potassium sorbate & sodium benzoate are fungistats in acid foods. Calcium propionate is a fungistat and anti-Bacillus in bread. Sodium nitrite prevents germination and growth of botulism endospores.

Gas chemosterilizers

Used in closed chambers. Highly reactive molecules react with functional groups on amino acids of proteins. Includes ethylene oxide, propylene oxide, and B-propiolactone. All are suspected carcinogens.

Peroxygens

Oxidizing agents and highly reactive (ROS). Oxidize cellular components of microbes. Includes ozone, hydrogen peroxide, benzoyl peroxide, and peracetic acid.

Chemotherapy

Treatment of disease with a chemical substance.

Antimicrobial chemotherapy

Antimicrobial drugs that act by interfering with growth of microorganisms.

Selective toxicity

Ideal drug kills harmful microorganisms without damaging host.

Therapeutic index

Degree of selectivity of the drug; a high therapeutic index is a high degree of selectivity and therefore a relatively safe drug.

Broad spectrum antimicrobial drugs

Affect both gram positive and gram-negative organisms. More likely to damage beneficial normal flora and greater chance of superinfection.

Narrow spectrum antimicrobial drugs

Affect one type or a narrow group of organisms.

Synergism

The combined effect of two drugs given simultaneously can be greater than the sum of their individual effects.

Antagonism

The combined effect of two drugs given simultaneously can be less than the sum of their individual effects.

Drug resistance

A pathogen that is no longer affected by a drug.

Mutation

Microbe undergoes a genetic change so that it is no longer affected by a drug.

Biofilms

Unicellular or multicellular communities of bacteria attached to a surface.

Antibiotics

Chemicals of microbial origin (from bacteria and fungi) that have antimicrobial activity, produced by many soil organisms to inhibit competing organisms.

Semi-synthetic drugs

Produced in the lab by modifying a natural molecule originally produced by an organism, typically an antibiotic.

Modes of Drug Action

Inhibition of cell wall synthesis, inhibition of protein synthesis, inhibition of nucleic acid replication and transcription, injury to plasma membrane, inhibition of synthesis of essential metabolites.

Antimetabolite

Competitive inhibitor example sulfanilamide which inhibits PABA's conversion to folic acid.

B-lactam ring

Core structure containing of Penicillin Molecules preventing cross-linking of peptidoglycan which prevents final construction of cell wall

Quinolones

Antimicrobial drug that Inhibit DNA synthesis, Broad spectrum; urinary tract infections

Antifungal Drugs

Most inhibit plasma membrane biosynthetic pathways.

Antiviral Drugs

Existing ones are effective only against an extremely limited group of diseases, HIV.

Antiprotozoan/Antihelminthic Drugs

Include Metronidazole (Flagyl) which is widely used.