Terminology and Principles of Microbial Control

Antisepsis

reduction in the number of microorganisms and viruses on living tissue

Aseptic

refers to an environment or procedure free of pathogenic contaminants

-cide/-cidal

indicating destruction of a type of microbe. Ex: bactericide, fungicide

Disinfection

destruction of most microorganisms and viruses on nonliving tissue

Pasteurization

use of heat to destroy pathogens and reduce the number of spoilage microorganisms in foods and beverages

Sanitization

removal of pathogens from objects to meet public health standards

Antimicrobials

disinfecting agents that are naturally produced by microorganisms

stasis/-static

indicating inhibition, but not complete destruction of a microbe

Sterilization

destruction of all microorganisms and viruses in or on an object

Moist heat - Boiling

Kills vegetative cells of bacteria and fungi, protozoa, most viruses; Boiling time is critical

Moist heat - Autoclaving

Pressure applied to boiling water prevents steam from escaping; Autoclave conditions - 121ºC, 15 psi, 15 min

Moist heat - Pasteurization

Used for milk, ice cream, yogurt, and fruit juices; Not sterilization; Heat-tolerant microbes survive

Incineration

Burn items completely; Can be used to discard public waste; An effective means of sterilization

Refrigeration and Freezing

Decrease microbial metabolism, growth, and reproduction; Refrigeration halts growth of most pathogens

Desiccation and Lyophilization

Drying inhibits growth because of removal of water; Lyophilization used for long-term preservation of microbial cultures

Radiation - Ionizing radiation

Wavelengths shorter than 1 nm; Ejects electrons from atoms to create ions; Ions disrupt hydrogen bonding, can denature DNA

Alcohols

Intermediate-level disinfectants; Denature proteins and disrupt cytoplasmic membranes; More effective than soap in removing bacteria from hands

Phenolics

Intermediate to low-level disinfectants; Denature proteins and disrupt cytoplasmic membranes; Have disagreeable odor and can cause skin irritation

Halogens

Intermediate-level antimicrobial chemicals; Believed to damage enzymes via oxidation or by denaturation

Oxidizing Agents

Peroxides, ozone, and peracetic acid; Kill by oxidation of microbial enzymes; High-level disinfectants and antiseptics

Gaseous agents

Ethylene oxide: highly reactive microbial and sporicidal gas; Extremely toxic to humans

Surfactants

"Surface active" chemicals; Reduce surface tension of solvents; Soaps and detergents

Heavy Metals

Heavy-metal ions denature proteins; Low-level bacteriostatic and fungistatic agents

gonorrhoeae

Once used in newborns' eyes

Thimerosal

Used to preserve vaccines

Practice stopped in 1999

Because mercury is a metabolic poison

Copper

Controls algal growth

Aldehydes

Compounds containing terminal -CHO groups

Aldehydes usage

Used in aqueous solutions

Aldehydes effect

Denature proteins

Aldehydes hazard

Hazardous to humans

Glutaraldehyde

Disinfects and sterilizes

Formalin

Combination of formaldehyde and water used in embalming and disinfection

Drugs

Chemicals that affect physiology in any manner

Chemotherapeutic agents

Drugs that act against diseases

Antimicrobial agents

Drugs that treat infections

Paul Ehrlich

Discovered 'magic bullets' in the form of arsenic to combat syphilis

Alexander Fleming

Discovered penicillin's antimicrobial properties

Selman Waksman

Coined the term 'antibiotic' when he discovered Streptomyces

Penicillium chrysogenum

Mold that exhibits antibiotic effect

Selective toxicity

Key mechanism of antimicrobial action

Inhibition of Cell Wall Synthesis

Bacteria have weakened cell walls and eventually lyse

Examples of Cell Wall Synthesis inhibitors

Vancomycin, cycloserine, bacitracin, isoniazid, ethambutol

Inhibition of Protein Synthesis

Drugs can selectively target translation

Prokaryotic ribosomes

70S (30S and 50S)

Eukaryotic ribosomes

80S (40S and 60S)

Examples of Protein Synthesis inhibitors

Streptomycin, gentamicin, tetracyclines, erythromycin

Disruption of Cytoplasmic Membranes

Some drugs form channel through cytoplasmic membrane and damage its integrity

Amphotericin B

Affects fungal membranes

Inhibition of Metabolic Pathways

Antimetabolic agents can be effective when metabolic processes of pathogen and host differ

Quinolones

Interfere with the metabolism of malaria parasites

Inhibition of Nucleic Acid Synthesis

Several drugs block DNA replication or mRNA transcription

Efficacy tests

Ascertained by diffusion susceptibility test (Kirby-Bauer test), minimum inhibitory concentration (MIC) test, and minimum bactericidal concentration (MBC) test

Etest

Combines the susceptibility and MIC test

Efficacy

The ability of an antimicrobial drug to produce a desired effect.

Zone of Inhibition

A clearing zone with no growth of bacteria measured as a diameter after drugs diffuse out of a paper disk placed on a bacterial lawn.

Turbidity

Measures the cloudiness of a fluid, used with broth dilution test.

Topical application

Application of a drug for external infections.

Oral route

Administration of a drug that requires no needles and is self-administered.

Intramuscular administration

Delivers drug via needle into muscle.

Intravenous administration

Delivers drug directly to the bloodstream.

Blood brain barrier

A barrier that most drugs cannot pass, making it difficult to treat brain infections.

Toxicity

The cause of many adverse reactions that are poorly understood, potentially toxic to kidneys, liver, or nerves.

Allergies

Rare but potentially life-threatening allergic reactions to drugs.

Anaphylactic shock

A severe allergic reaction that can be life-threatening.

Disruption of normal microbiota

May result in secondary infections and overgrowth of normal flora causing superinfections.

Superinfections

Infections that occur due to the overgrowth of normal flora.

Resistance to Antimicrobial Drugs

The ability of pathogens to withstand the effects of drugs that once killed them or inhibited their growth.

Natural resistance

Resistance that some pathogens have inherently.

Acquired resistance

Resistance developed through new mutations of chromosomal genes or transformation of bacterial DNA.

Multiple Resistance

When a pathogen acquires resistance to more than one drug.

Superbugs

Bacteria that have become resistant to multiple antibiotics.

Retarding Resistance

Strategies to slow down the development of resistance, such as using antimicrobials only when necessary.

Second-generation drugs

New variations of existing drugs developed to combat resistance.

Third-generation drugs

Further developed variations of existing drugs to address resistance.

Probiotics

Microbial antagonism used as an alternative to chemotherapy.