A bactericide or bacteriocide is a substance that kills bacteria and, preferably, nothing else. Bactericides are either disinfectants, antiseptics or antibiotics.
Important Functional Groups in a Bactericidal Substance
The most used bactericidal disinfectants are those applying
- active chlorine (i.e., hypochlorites, chloramines, dichloroisocyanurate and trichloroisocyanurate, wet chlorine, chlorine dioxide etc.),
- active oxygen (peroxides, such as peracetic acid, potassium persulfate, sodium perborate, sodium percarbonate and urea perhydrate),
- iodine (iodpovidone (povidone-iodine, Betadine), Lugol's solution, iodine tincture, iodinated nonionic surfactants),
- concentrated alcohols (mainly ethanol, 1-propanol, called also n-propanol and 2-propanol, called isopropanol and mixtures thereof; further, 2-phenoxyethanol and 1- and 2-phenoxypropanols are used),
- phenolic substances (such as phenol (also called "carbolic acid"), cresols (called "Lysole" in combination with liquid potassium soaps), halogenated (chlorinated, brominated) phenols, such as hexachlorophene, triclosan, trichlorophenol, tribromophenol, pentachlorophenol, Dibromol and salts thereof),
- cationic surfactants, such as some quaternary ammonium cations (such as benzalkonium chloride, cetyl trimethylammonium bromide or chloride, didecyldimethylammonium chloride, cetylpyridinium chloride, benzethonium chloride) and others, non-quarternary compounds, such as chlorhexidine, glucoprotamine, octenidine dihydrochloride etc.),
- strong oxidizers, such as ozone and permanganate solutions;
- heavy metals and their salts, such as colloidal silver, silver nitrate, mercury chloride, phenylmercury salts, copper sulfate, copper oxide-chloride etc. Heavy metals and their salts are the most toxic, and environment-hazardous bactericides and therefore, their use is strongly oppressed or canceled; further, also
- properly concentrated strong acids (phosphoric, nitric, sulfuric, amidosulfuric, toluenesulfonic acids) and
- alkalis (sodium, potassium, calcium hydroxides),
such as of pH < 1 or > 13, particularly under elevated temperature (above 60°C), kills bacteria.
As antiseptics (i.e., germicide agents that can be used on human or animal body, skin, mucoses, wounds and the like), few of the above mentioned disinfectants can be used, under proper conditions (mainly concentration, pH, temperature and toxicity toward man/animal). Among them, important are some
- properly diluted chlorine preparations (f.e. Daquin's solution, 0.5% sodium or potassium hypochlorite solution, pH-adjusted to pH 7 - 8, or 0.5 - 1% solution of sodium benzenesulfochloramide (chloramine B)), some
- iodine preparations, such as iodopovidone in various galenics (oinment, solutions, wound plasters), in the past also Lugol's solution,
- peroxides as urea perhydrate solutions and pH-buffered 0.1 - 0.25% peracetic acid solutions,
- alcohols with or without antiseptic additives, used mainly for skin antisepsis,
- weak organic acids such as sorbic acid, benzoic acid, lactic acid and salicylic acid
- some phenolic compounds, such as hexachlorophene, triclosan and Dibromol, and
- cation-active compounds, such as 0.05 - 0.5% benzalkonium, 0.5 - 4% chlorhexidine, 0.1 - 2% octenidine solutions.
Others are generally not applicable as safe antiseptics, either because of their corrosive or toxic nature.
Bactericidal antibiotics kill bacteria; bacteriostatic antibiotics only slow their growth or reproduction.
Penicillin is a bactericide, as are cephalosporins, all belonging to the group of β-lactam antibiotics. They act in a bactericidal manner (by disrupting cell wall precursor leading to lysis).
Aminoglycosidic antibiotics are usually considered bactericidal, although they may be bacteriostatic with some organisms. They act by binding irreversibly to 30s ribosomal subunit, reducing translation fidelity leading to inaccurate protein synthesis). The other effect is the inhibition of protein synthesis due to premature separation of the complex between mRNA and ribosomal proteins. The final result is bacterial cell death.
Other bactericidal antibiotics include the fluoroquinolones, nitrofurans, vancomycin, monobactams, co-trimoxazole, and metronidazole.