Physical and Chemical Control of Microbes & Antimicrobial Treatment

Comprehensive vocabulary flashcards covering physical and chemical control methods, thermal parameters, sterilization vs. disinfection, radiation, chemical germicides, antimicrobial mechanisms of action, major antibiotic and antiviral classes, and susceptibility testing.

Sterilization

A process that completely destroys or removes all viable microorganisms, including bacterial endospores and viruses, from inanimate objects.

Disinfection

The destruction or removal of vegetative pathogens but not bacterial endospores, normally applied only to inanimate objects.

Antisepsis (Degermation)

The application of chemical agents to exposed body surfaces, wounds, and surgical incisions to destroy or inhibit vegetative microbes.

Decontamination (Sanitization)

A cleansing technique that mechanically removes most microorganisms and debris from animate or inanimate surfaces to reduce contamination to safe levels.

Relative Resistance Hierarchy of Microbes

The order of microbial resistance to physical and chemical control methods, ranging from the most resistant forms (prions and bacterial endospores) to the least resistant forms (most gram-positive bacteria and enveloped viruses such as SARS-CoV-2).

Bacterial Endospores

The most resistant microbial entities (except prions) whose destruction serves as the primary benchmark and goal for sterilization.

Critical Medical Devices

Medical items expected to enter sterile tissues, such as surgical instruments, syringes, and catheters, which require complete sterilization.

Semicritical Medical Devices

Medical instruments that come into contact with mucous membranes, such as respiratory equipment and thermometers, requiring at least intermediate- to high-level disinfection.

Noncritical Medical Devices

Devices that do not touch the patient or are expected to touch only intact skin, including blood pressure cuffs, straps, and electrodes.

Microbicidal Agent

A physical or chemical agent that directly kills microorganisms (e.g., bactericides, fungicides, virucides, and sporicides).

Microbiostatic Agent

An agent that inhibits the growth and multiplication of microbes without killing them outright, permitting resumption of growth if the agent is removed.

Thermal Death Time (TDT)

The shortest length of time required to kill all test microbes in a sample at a specified temperature.

Thermal Death Point (TDP)

The lowest temperature required to kill all microbes in a liquid suspension within a period of $10\,\text{minutes}$.

Autoclave

A specialized chamber that subjects steam to elevated pressure ($15\,\text{psi}$, producing pure steam at $121^\circ\text{C}$ for $20\,\text{minutes}$) to achieve true sterilization of heat-resistant materials.

Incineration

A dry heat sterilization method that uses an open flame (Bunsen burner reaching up to $1{,}870^\circ\text{C}$) or an electric furnace ($800^\circ\text{C}\text{ to }6{,}500^\circ\text{C}$) to reduce microbes to ashes and gas.

Dry-Air Oven

An electric or gas chamber with heating coils that achieves sterilization through dry heat by exposure to $150^\circ\text{C}\text{ to }180^\circ\text{C}$ for $2\text{ to }4\,\text{hours}$.

Desiccation

The removal of moisture from vegetative cells directly exposed to normal room air, causing dehydration and preservation of some microbes while killing delicate ones.

Lyophilization

A preservation method combining instantaneous deep freezing with vacuum drying to maintain microbial cultures in a viable, dormant state.

Ionizing Radiation

High-energy radiation (gamma rays, X rays, cathode rays) that strips electrons from atoms and induces catastrophic double-strand breaks in DNA; used for cold sterilization of heat-sensitive materials.

Nonionizing Radiation (UV Rays)

Radiation with wavelengths of $100\text{ to }400\,\text{nm}$ (peak germicidal activity at $260\,\text{nm}$) that penetrates surfaces poorly and kills microbes by inducing pyrimidine/thymine dimers in DNA.

Filtration

A mechanical method of microbial removal that strains fluids or air through membrane pores ranging from $8\,\mu\text{m}$ down to ultrafine $0.02\,\mu\text{m}$, trapping microbes while letting liquid or gas pass.

Osmotic Pressure Control

The preservation of foods via high salt or sugar concentrations, which generates a hypertonic environment that induces plasmolysis in bacteria and prevents multiplication.

High-Level Germicides

Chemical sterilants capable of killing all microorganisms, including bacterial endospores, when applied properly to non-heat-sterilizable critical medical items.

Intermediate-Level Germicides

Chemical agents that destroy fungal spores, resistant pathogens such as Mycobacterium tuberculosis, and viruses, but do not kill bacterial endospores.

Low-Level Germicides

Disinfectants that eliminate vegetative bacteria, vegetative fungi, and some viruses, used to clean noncritical environmental surfaces and clinical items.

Halogens

A chemical group of antimicrobials (chlorine, iodine, fluorine, bromine) that permanently denature cellular enzymes and suspend essential metabolic reactions.

Iodophors

Complexes of elemental iodine and a polymer/alcohol (e.g., Betadine, Povidone) that release free iodine slowly to provide antisepsis while reducing tissue staining and skin irritation.

Chlorhexidine

A complex organic antiseptic containing chlorine and two phenolic rings that targets bacterial cell membranes and denatures proteins; commonly used for surgical hand scrubs and preoperative skin preps.

Surfactants

Amphipathic polar molecules that insert into the hydrophobic regions of cell membranes, disrupting surface tension and causing the selective permeability barrier to break down.

Quaternary Ammonium Compounds (Quats)

Cationic detergents whose positively charged end binds to negatively charged bacterial surface proteins while their hydrocarbon chain disrupts the cytoplasmic membrane.

Oligodynamic Effect

The ability of extremely small quantities of heavy metals and metallic ions (such as mercury and silver) to exert microbicidal effects by binding to and inactivating functional groups of cellular proteins.

Glutaraldehyde

A high-level dialdehyde liquid sterilant that irreversibly crosslinks and disrupts cellular proteins and enzymes; kills endospores and is used on delicate hospital scopes and dialysis units.

Ethylene Oxide (ETO)

A colorless, explosive, and carcinogenic gas used in a chemiclave to sterilize heat-sensitive prepackaged plastics and medical devices by strongly alkylating DNA and proteins.

Prophylaxis

The clinical use of an antimicrobial drug to prevent the development of an anticipated infection in a patient at risk.

Semisynthetic Drugs

Antimicrobial agents that are isolated from natural microbial sources and subsequently chemically modified in a laboratory to broaden their spectrum or reduce susceptibility to inactivation.

Synthetic Drugs

Antimicrobial compounds synthesized entirely through laboratory chemical reactions rather than harvested from natural living organisms.

Broad-Spectrum Antimicrobial

An antimicrobial agent that is effective against a wide variety of microbial types, such as tetracyclines active against both gram-positive and gram-negative bacteria.

Narrow-Spectrum Antimicrobial

An antimicrobial agent with targeted effectiveness against a limited array of microbial groups, such as polymyxin targeting gram-negative bacteria or bacitracin targeting gram-positive bacteria.

Streptomyces

A bacterial genus that produces a wide variety of therapeutic agents, including antibiotics (tetracycline, streptomycin, vancomycin, clindamycin), antifungals (nystatin), antiprotozoals (ivermectin), and anticancer drugs (bleomycin).

Kirby-Bauer Technique

An agar diffusion method in which antibiotic-impregnated paper discs are placed on a bacterial lawn, producing measurable circular zones of inhibition that determine antimicrobial susceptibility.

Antibiogram

A comprehensive profile or chart summarizing the antimicrobial sensitivity patterns of an isolated microbial pathogen.

Minimum Inhibitory Concentration (MIC)

The lowest concentration (highest dilution) of an antimicrobial drug that visibly inhibits the growth of a test microorganism in vitro.

Selective Toxicity

The central principle of antimicrobial chemotherapy requiring a drug to kill or inhibit microbial pathogens without concurrently harming host tissues.

Superinfection

A secondary infection resulting from the depletion of normal resident microbiota by broad-spectrum antibiotics, permitting resistant pathogens such as Candida albicans or Clostridioides difficile to overgrow.

Beta-Lactam Ring

A four-membered cyclic amide structure found within penicillins and cephalosporins that inhibits transpeptidases essential for bacterial cell wall cross-linking.

Cephalosporins

A class of beta-lactam antibiotics originating from Cephalosporium acremonium that block cell wall peptidoglycan synthesis; includes generations ranging from first (cefazolin) to fifth (ceftobiprole).

Bacitracin

A narrow-spectrum peptide antibiotic that blocks cell wall synthesis and repair, commonly applied topically in Neosporin for superficial staphylococcal and streptococcal infections.

Vancomycin

A narrow-spectrum glycopeptide antibiotic targeting cell wall synthesis; clinically reserved for severe staphylococcal infections resistant to methicillin (MRSA) or in patients allergic to penicillin.

Aminoglycosides

Antibacterial drugs (including streptomycin) that bind specifically to the $30\text{S}$ ribosomal subunit, misreading mRNA and synthesizing incorrect proteins.

Tetracyclines

Broad-spectrum antibiotics that bind to the $30\text{S}$ ribosomal subunit and block the entry of aminoacyl-tRNA, completely halting protein translation.

Sites of Ribosomal Inhibition

Specific subunits on the bacterial $70\text{S}$ ribosome targeted by antibiotics: the $50\text{S}$ subunit (targeted by oxazolidinones, pleuromutilins, and erythromycin) and the $30\text{S}$ subunit (targeted by aminoglycosides and tetracyclines).

Sulfonamides (Sulfa Drugs)

Synthetic metabolic competitive inhibitors that disrupt folic acid synthesis by mimicking PABA, preventing the production of tetrahydrofolate needed for bacterial DNA and RNA synthesis.

Fluoroquinolones

Broad-spectrum synthetic antibiotics (such as ciprofloxacin) that inhibit bacterial DNA gyrase, preventing the unwinding and replication of bacterial DNA.

Polymyxins (Colistins)

Narrow-spectrum antibiotics that interact with membrane phospholipids and lipopolysaccharides, disrupting selective permeability in gram-negative bacteria.

Amphotericin B

A macrolide polyene antifungal that binds to ergosterol in fungal cell membranes, causing leakage of ions and macromolecules; used against histoplasmosis and Cryptococcus meningitis.

Echinocandins

A class of antifungal drugs (e.g., micafungin, caspofungin) that selectively inhibit fungal cell wall synthesis, used against Candida and Aspergillus infections.

Reverse Transcriptase Inhibitors (RTIs)

Antiretroviral agents, including nucleoside analogues like zidovudine (AZT) and non-nucleoside inhibitors like nevirapine, that stop reverse transcriptase in HIV to block viral DNA production.

Paxlovid

An oral antiviral medication that acts as a protease inhibitor, binding to the main protease of SARS-CoV-2 to block protein cleavage and produce inactive, noninfectious viral particles.