B2: chemical methods

are chemicals better suited for sterilization or disinfection?

chemical methods generally can’t achieve sterility

• few chemicals are so harmful to life that absolutely everything will be killed 100%

but chemicals can make excellent disinfectants

what hardy genus are phenolics are useful against?

Mycobacterium

what is the mechanism of phenolics (phenol, chlorhexidine)

break down lipid-containing structures by making it an amphipathic molecule

• the plasma membrane

• the waxy cell wall of Mycobacterium → causes tuberculosis

what are the pros of phenolics?

stable

works around other organic compounds

kills tubercular bacteria

what are the cons of phenolics?

stinky

irritating to the skin

potentially toxic

have been replaced in most settings

what is chlorhexidine?

phenolic derivative replacing iodine tincture as an antiseptic

why did chlorhexidine replace iodine tincture?

some patients have a strong reaction to iodine

may have neurological effects on newborns → absorb the iodine and disrupt their thyroid

what is the mechanism of halogens?

disrupt protein function

examples of halogens

iodine

chlorine

hypochlorite (chlorine bleach)

what is iodine effective against?

effective against all kinds of bacteria and many viruses

why is chlorine used?

can be used as a gas or salt to disinfect surfaces or water

how is hypochlorite (chlorine bleach) used?

used as an aqueous (dissolved in water) solution

what are the pros of halogens?

effective against a wide variety of pathogens

what are the cons of halogens?

toxic at high levels

inactivated by light, high pH, excess organic matter

what is the mechanism of alcohols?

denatures proteins and disrupts membranes

helps mechanical removal of microbes and dirt (good sanitation agent)

when is alcohols most effective?

most effective when mixed with water

70:30 mix

why is alcohol not effective at higher concentrations?

cell coagulates the proteins around the cell → becomes protected from the alochol

what are the pros of alochols?

evaporates rapidly, leaving no residue after use

what are the cons of alcohols?

some bacteria and many viruses are resistant

little effect on endospores

examples of heavy metals

mercury, copper, silver

silver nitrate

how effective is mercury, copper, and silver?

small amounts can kill bacteria

what is silver nitrate used for?

silver nitrate (1%) solution used to be placed in the eyes of newborns to prevent infection

bandages and catheters with silver in them are coming into use → effective against antibiotic resistant bacteria

what is the mechanism of heavy metals?

denatures or inhibits proteins

how do heavy metals denature/inhibit proteins?

many enzymes depend on metals to function properly as cofactors

if you have the wrong metals or too much of the right metals → it’ll cause proteins to malfunction

what are the pros of heavy metals?

effective with small amounts of metal

very stable

what are the cons of heavy metals?

can be toxic very stable

what are surfactants?

soap!

how is soap or detergent effective?

some antiseptic properties

what is a more effective surfactant?

cationic detergents (positively charged)

what are quaternary ammonium compounds (quats)?

positively charged soaps that are really good at killing microbes in addition to being good surfaces

what is the mechanism of surfactants

disrupts membranes and cell walls → integrate themselves into membranes and causes them to fall apart

also good sanitizers → since they’re amphipathic, can get oily stuff to mix with aqueous stuff

what are the pros of surfactants?

non-toxic

what are the cons of surfactants?

multiple dangerous microbes are highly resistant to surfactants

examples of sterilant gases

ethylene oxide (ETO)

propylene oxide

what are sterilant gases highly effective for?

germicide, sporicide

what are sterilant gases used for?

used to sterilize heat-sensitive medical equipment

what is the mechanism of sterilant gases?

denatures proteins and damages DNA

what are the pros of sterilant gases

powerful sterilant with potent sporicidal activity

what are cons of sterilant gases?

toxic

highly explosive

what are aldehydes (-CHO functional groups)?

strong sterilants but highly toxic

some weak aldehydes can be used as disinfectants

examples of aldehydes

formaldehyde

glutaraldehyde

what is the mechanism of aldehydes?

denatures proteins

what are the pros of aldehydes?

incredibly effective germicides

can actually sterilize rather than just disinfect

what are the cons of aldehydes?

highly toxic

potentially carcinogenic → dangerous to humans

examples of oxidizing agents

ozone (O3)

hydrogen peroxide

what is ozone (O3) used for?

can substitute for chlorine to disinfect water

how effective is hydrogen peroxide (H2O2) liquid/gas

good for disinfecting non-living surfaces → sporicide!

some use as an antiseptic, but may cause damage

what is hydrogen peroxide good against?

particularly good against anaerobes, endospores

what is hydrogen peroxide gas used on?

vaporized gas used on medical equipment

what is the mechanism of oxidizing agents (ozone, hydrogen peroxide)?

altered protein function

DNA damage

what are the pros of oxidizing agents?

strong germicides, sporicides

what are the cons of oxidizing agents?

unstable, can cause tissue damage

acid agents

corrosive and toxic, most are rarely used → not used as a disinfectant

examples of organic acids

lactic acid

acetic acid

propionic acid

what are acid agents used for?

used as preservatives to keep food from spoiling

safe to eat; restrict growth of common food spoilage microbes

what are some examples of alkaline agents?

ammonium hydroxide

sodium hydroxide

what are alkaline agents used for?

used as cleansing agents

one of the only agents with activity against prions

what is the mechanism of acid and alkaline agents?

denature proteins

what are the pros of acid and alkaline agents?

acids are safe and effective food preservatives

bases can inactivate prions

what are the cons of acid and alkaline agents?

irritating and potentially damaging to skin, wounds

what microbes are most resistant to antimicrobial agents?

spores and mycobacteria present the greatest challenge for proper sterilization or disinfection

which ones are effective against spores?

sterilant gases

hydrogen peroxide

which ones are effective against mycobacteria?

phenols