BIOL 251 - Ch. 13 Study Points, Individual chemicals

Critical items

Used inside the body and penetrate body tissue

Must be sterile

Surgical instruments, catheters, IV fluids

Semi-critical items

Contacts mucous membrane and nonintact skin

Doesn’t penetrate body tissues

GI endoscopes, some respiratory therapies

Non-critical items

Unbroke skin

Stethoscope

What are the various methods of control?

Sterilization

Aseptic technique

Commercial sterilization

Disinfection

Pasteurization

Decontamination

Sanitation

Degermining

Antiseptics

Sterilization

Eliminates all forms of life (except prions)

Lab, medical, manufacturing, and food industry settings

Achieved thru physical means - high heat, pressure, or filtrations

Achieved thru chemical means - sterilant

Aseptic technique

Prevents contamination of sterile surfaces

Protocols that maintain sterility (asepsis)

Prevent contamination of patients (avoiding sepsis)

Sterile field - necessary for medical procedures that carry contamination risk

Commercial sterilization

Uses heat at a temperature low enough to preserve food quality but high enough to destroy common pathogens

Main target are C. botulinum spores

Disinfection

Inactivates most microbes on fomite surface using antimicrobial chemicals or heat

Not sterilization

Pasteurization

Reduces number of spoilage organisms and pathogens while maintaining food quality

Not sterile and product will still spoil

High-temperature short-time (HTST)

Ultra-high temperature (UHT)

HTST pasteurization

72C for 15 seconds

Lowers bacterial numbers while preserving the quality of the milk

UHT pasteurization

138C for 2 or more seconds

Can be stored for a long time in sealed containers without being refrigerated

Helpful method when refrigeration is limited

Decontamination

Reduces pathogens to a level considered safe

Sanitation

Reduces microbial populations to levels acceptable for public health

Degerming

Significantly reduces microbial numbers

Handwashing

Antiseptics

Antimicrobial chemicals safe for use on skin surfaces

Hydrogen peroxide, isopropyl alcohol

What are the conditions in an autoclave?

121 C and 15 psi for 15 minutes

Sterilizes and kills endospores

Moist heat

Denatures proteins

Relatively fast, reliable, safe, and inexpensive

Widely used

Boiling

Destroys most microbes and viruses but not endospores

Not a form of sterilization

Incineration

Burns cell components to ashes

Flaming inoculating loops

Destroy medical wastes and contaminated animal carcasses

Dry heat ovens

Destroys cell components and denatures proteins

Less efficient than moist heat and require longer times and higher temperatures

What are physical methods of microbial control?

Refrigeration/freezing

Radiation

Filtration

Refrigeration/freezing

Temperatures between 0-7C

Inhibits microbial metabolism, slowing the growth of microbes

Preserves refrigerated products such as foods or medical supplies

Below -2C stops microbial growth and may kill susceptible organisms

Cultures and medical specimens can be stored for long periods at ultra-low temperatures - at or below -70C

Radiation

Causes damage to DNA and potentially to plasma membrane

Used to sterilize heat sensitive materials - medical equipment, surgical supplies, medications

Some endospores can be resistant

3 sources - gamma radiation, x-rays, electron accelerators

Filtration

Sterilize

Air filtration - HEPA filter removes nearly all microbes

Membrane filtration - liquid filtration, for heat sensitive fluids, traps microbes on filter

What are the different types of germicidal chemicals?

Sterilants

High-level disinfectants

Intermediate-level disinfectants

Low-level disinfectants

Sterilants

Treat heat sensitive critical instruments

Kills endospores, Mycobacterium spp., fungi, and all viruses

High-level disinfectants

Treat semi-critical instruments

Kills some endospores, Mycobacterium spp., all fungi, and all viruses

Intermediate-level disinfectants

Disinfects non-critical instruments

Doesn’t kill endospores, kills some Mycobacterium spp., all fungi, some non-enveloped viruses, and all enveloped viruses

Low-level disinfectants

General purpose

Disinfect furniture, floors, and walls

Doesn’t kill endospores and Mycobacterium spp., kills some fungi and enveloped viruses but no non-enveloped viruses

How is the appropriate chemical chosen?

Toxicity

Presence of organic matter

Compatibility with material being treated

Residue

Cost and availability

Ease of use

Storage/stability

Environmental risk

Alcohols

Kill bacteria and fungi but not endospores or non-enveloped viruses

Denature proteins (inhibit cell metabolism)

Disrupt membranes (cell lysis)

Antiseptic on skin - swabbing the skin for degerming before needle injection; active ingredient in instant hand sanitizer

SARS-CoV-2 is an enveloped virus and may be inactivated by alcohol-containing products

Aldehydes

Inactivates enzymes and nucleic acids

Strong, broad-spectrum disinfectant

Kills bacteria, fungi, viruses, and endospores - sterilization at low temperatures (alternative for autoclaving/heat sterilization)

Irritating to skin - not a good antiseptic

2% alkaline gluteraldehyde

Most commonly used chemical for
sterilizing heat sensitive medical items

Formaldehyde

Aldehyde

Preserves biological specimens by crosslinking proteins

Formalin

Aldehyde

Used in vaccines to kill bacteria and inactivate viruses

Ethylene oxide

Gaseous sterilizing agent - fabric, pillows, artificial hips, pacemakers, petri dishes

Highly penetrating and can sterilize items within plastic bags such as catheters, disposable items in labs and clinical settings

Items are sterilized in a special chamber

Cold sterilization - good for heat sensitive items

Bisbiguanides

Antiseptics before surgery - surgeon hand scrub

Broad-spectrum activity against yeasts, Gram-positive/negative bacteria, and enveloped viruses - exception is Pseudomonas aeruginosa which may develop resistance on repeated exposure; not effective for Mycobacterium, non-enveloped viruses, or spores

Chlorhexidine

Bisbiguanide

Common ingredient in skin creams, disinfectants, mouthwashes/oral rinses, catheters, and surgical mesh

Halogens

Chlorine compounds can irritate skin, nose, and eyes - some protozoan cysts are resistant to chlorine (Cryptosporidium)

Chlorine

Halogen

Disinfect waste liquid, surfaces, drinking water

Swimming pools

Sodium hypochlorite (bleach)

Halogen

Kill bacteria and viruses

Less reliable when organic material is present

Chloramine

Halogen

Disinfect drinking water - tablets used by military

Chlorine dioxide

Halogen

Gaseous agent used for fumigation and sterilization of enclosed areas

Commonly used for disinfection of water

Iodine

Halogen

Oxidizes cellular components - destabilized macromolecules

Heavy metals

Kill microbes by binding to proteins, which inhibits enzymatic activity

Small concentrations of metal ions accumulate in cells - cause proteins to denature

Not selectively toxic to microbial cells

Mercury

Heavy metal

Not used in the US due to toxicity concerns

Silver

Heavy metal

Used as an antiseptic

Some catheters and bandages contain it

Silvadene cream

Heavy metal

Topical for burn wounds

Silver nitrate drops

Were used for ophthalmia neonatorum (eye infection in newborn)

Replaced by antibiotic creams

Copper

Heavy metal

Algacide

Zinc chloride

Heavy metals

Mouthwashes

Phenolics

1800s - scientists started using chemicials for disinfection

1860s - Joseph Lister began using carbolic acid as a disinfectant for the treatment of surgical wounds

Compound in mouthwashes and throat lozenges

Less toxic than phenol - disrupt membrane, denature proteins to inhibit microbial growth

Listerine, Lysol

pHisoHex

Phenolic

Handwashing in hospital settings

Effective for Staph and Strep that cause skin infections

Triclosan

Phenolic

In many antibacterial products until 2016 - FDA banned

Regular soap was just as effective as soaps containing this

What are the targets in bacterial cells that are affected by germicidal chemicals?

Cytoplasmic membrane

Proteins

DNA

How does the assay for testing the effectiveness of germicidal chemicals work?

Disk-diffusion assay is used to determine effectiveness of chemical agents against a particular microbe

Plate is inoculated with various antimicrobial discs

Zone of inhibition around each disc indicates how effective the antimicrobial agent is

No zone of inhibition = doesn’t work