Merck Manual

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Professional Version

Acids and Alkalies as Antiseptics and Disinfectants for Use With Animals


Diane D. Addie

, PhD, BVMS,

Reviewed/Revised Jul 2022 | Modified Nov 2022

Acids as Antiseptics and Disinfectants for Use With Animals

Hydrogen ions (H+) are bacteriostatic at pH ~3–6 and bactericidal at pH <3. Strong mineral acids (HCl, H2SO4, etc) in concentrations of 0.1–1 N have been used as disinfectants; however, their corrosive action limits their usefulness. Acids are used as food preservatives (eg, benzoic acid, citric acid), antiseptics (eg, boric acid, acetic acid), fungicides (eg, salicylic acid, benzoic acid), spermatocides (eg, acetic acid, lactic acid), and cauterizing agents (strong mineral acids). Skin and hides that have been contaminated by anthrax spores can be disinfected with 2.5% HCl.

Un-ionized weak organic acids can readily penetrate and disrupt bacterial cell membranes; examples include acetic and peracetic acid. Acetic acid (household vinegar) at 1% can be used in surgical dressings. At 5%, it is bactericidal to many bacteria, and dilute acetic acid has been used to treat otitis externa produced by Pseudomonas spp, Candida spp, Malassezia spp, or Aspergillus spp. However, because of acetic acid's unpleasant odor, commercially available disinfectants are generally used instead.

Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the formula CH3CO3H. It is weaker than acetic acid. Peracetic acid is generated in situ by some laundry detergents. Peracetic acid (at 0.23%) is combined with hydrogen peroxide (7.35%) to maintain the stability of the peracid. It is corrosive because of the acetic acid; however, additives in some commercial products decrease this adverse effect. The combination of PAA and hydrogen peroxide creates a useful sterilant and antiseptic, providing the broad antimicrobial spectrum and lack of harmful decomposition products of hydrogen peroxide with greater lipid solubility and freedom from inactivation by tissue catalase and peroxidase.

PAA with hydrogen peroxide can be used over wide ranges of temperature (0ºC–40ºC) and pH (3–7.5) and is not affected by organic matter. This disinfectant combination is effective against bacteria, yeasts, fungi, and viruses at concentrations of 0.001%–0.003% and is sporicidal at 0.25%–0.5%. Given this sporicidal property, peracetic acid products have been accepted worldwide in the food industry, including meat and poultry processing plants and dairies, and they are replacing traditional disinfectants for some medical devices.

Peracetic acid (0.2%) can also be applied to bandages to decrease microbial populations in severely contaminated or infected wounds.

Alkalies as Antiseptics and Disinfectants for Use With Animals

Hydroxyl ions (OH) also exert antimicrobial activity. At a pH of >9, OH inhibits most bacteria and many viruses. Hydroxides of sodium and calcium are used as disinfectants. Their irritant or caustic property usually precludes their application on tissues.

Calcium oxide (CaO)—ie, lime (hydrated or air-slaked lime)—soaked in water produces calcium hydroxide, Ca(OH)2. Aqueous suspensions of slaked lime are used to disinfect premises.

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