The words on this page are often used loosely, and the loose usage causes real mistakes: a bacteriostatic solution treated as if it were a sterilant, or a disinfectant used where a preservative was needed. The definitions below are the ones used in microbiology and in the pharmacopeias.
The definitions
| Term | Meaning | Example |
|---|---|---|
| Antimicrobial | The umbrella term for anything that kills microorganisms or stops them growing. | All of the terms below |
| Bacteriostatic | Stops bacteria from multiplying without necessarily killing them; growth resumes if the agent is removed or diluted below its effective concentration. | 0.9% benzyl alcohol in bacteriostatic water |
| Bactericidal | Kills bacteria. The distinction from bacteriostatic is one of degree and concentration: many agents are bacteriostatic at low concentration and bactericidal at higher concentration. | 70% ethanol on a surface |
| Fungistatic / fungicidal | The same distinction applied to yeasts and molds. An agent can be bactericidal but only fungistatic, which is the case for benzyl alcohol. | — |
| Preservative | An antimicrobial added to a product at a low concentration to prevent growth of organisms introduced during use or storage. A preservative protects a product; it does not sterilize it. | Benzyl alcohol, parabens, phenol |
| Antiseptic | An antimicrobial formulated for application to living tissue. | Alcohol hand rubs, iodine preparations |
| Disinfectant | An antimicrobial formulated for inanimate surfaces and objects. Disinfection reduces the number of organisms but does not necessarily eliminate spores. | Bleach solutions, quaternary ammonium compounds on benches |
| Sterilant / sterilization | A process or agent that destroys or removes all forms of microbial life, including bacterial spores, to a defined probability. | Steam autoclaving, dry heat, sterilizing filtration, ethylene oxide |
Where bacteriostatic water sits
Bacteriostatic water is sterile because of how it is manufactured and tested, and bacteriostatic because of the preservative it contains. Those are two different claims. Sterility describes the contents of the sealed vial at release. The preservative describes what happens after the seal is broken: organisms introduced during a withdrawal are prevented from multiplying, which is what makes a multi-use vial workable for a limited period. The preservative does not kill everything, does not act on spores, and does not turn a contaminated solution back into a sterile one. See is bacteriostatic water sterile? and what does bacteriostatic mean?
Three mistakes the definitions prevent
- Treating a preservative as a sterilant. Adding bacteriostatic water to a contaminated preparation does not decontaminate it. See common mistakes.
- Treating a disinfectant as a preservative. Disinfectants are formulated for surfaces at concentrations that would be incompatible with most solutions; they are not added to products.
- Assuming bacteriostatic means fungistatic to the same degree. It does not, which is one of the reasons opened vials are discarded after 28 days rather than kept until empty. See shelf life after opening.
Related
Glossary: 40 terms explained · Sterile vs. nonpyrogenic · Benzyl alcohol vs. other preservatives
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