Microbiology and Infection Prevention for Sterile Processing
Updated October 27, 2026
Sterile processing exists to stop infections from spreading through surgical instruments and devices. The CRCST exam’s Departmental Considerations area includes the microbiology behind that work. Here’s what to know, followed by free practice questions.
Types of microorganisms
| Type | Notes |
|---|---|
| Bacteria | Single-celled organisms; some form spores, the hardest form of life to kill |
| Viruses | Need a host cell to reproduce |
| Fungi | Includes yeasts and molds |
| Prions | Abnormal proteins that are extremely resistant to standard reprocessing; they need special procedures |
Bacterial spores are the hardest form to kill, which is why sterilization is defined as destroying all microorganisms, including spores, and why biological indicators use spores.
Biofilm
Biofilm is a layer of microorganisms protected by a slimy coating they produce. It can build up in lumens and crevices and protects microorganisms from disinfectants and sterilants. Prompt, thorough cleaning prevents biofilm from forming.
The chain of infection
An infection needs an infectious agent, a reservoir, a portal of exit, a mode of transmission, a portal of entry and a susceptible host. Sterile processing breaks the chain by making sure instruments can’t transmit microorganisms.
Bioburden
Bioburden is the number of microorganisms on an item. Cleaning reduces bioburden, which is why cleaning must always come before disinfection or sterilization.
Free practice questions
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Which form of microbial life is the hardest to kill?Answer: CBacterial spores are the most resistant form of microbial life, so sterilization processes are designed and tested to kill them.
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What is biofilm?Answer: BBiofilm is a community of microorganisms in a protective coating that shields them from disinfectants and sterilants.
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What does "bioburden" mean?Answer: ABioburden is the population of microorganisms on an item. Cleaning reduces it before disinfection or sterilization.
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Why must cleaning come before sterilization?Answer: DSoil and biofilm can shield microorganisms from the sterilant, so items must be clean for sterilization to work.
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Which infectious agents are extremely resistant to standard reprocessing and need special procedures?Answer: APrions, abnormal proteins linked to diseases such as Creutzfeldt-Jakob disease, resist standard reprocessing, so special procedures are used, following your facility's policy.
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How does sterile processing help break the chain of infection?Answer: BProperly cleaned, disinfected or sterilized instruments can't serve as a mode of transmission, breaking the chain.
Pass the CRCST exam on your first try
- All 207 questions on decontamination, disinfection, instruments, packaging, sterilization, storage, patient care equipment and professional skills
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