Cleaning, Decontamination and Disinfection is 21% of the scored CRCST exam. Answer 10 exam style questions on microbiology and infection prevention and see exactly which concepts would cost you points on test day.
Start the 10 questions →A new technician asks which type of microorganism is the hardest to kill and is therefore used to prove that a sterilization process works. What is the correct answer?
These questions cover microbial resistance hierarchy, prions, biofilm, chain of infection and modes of transmission. Each one shows the correct answer and why every other option is wrong, so a miss tells you exactly what to review before the CRCST.
Prefer to read first? Every question from the practice set above, with the correct answer and why each wrong option is wrong.
Answer: B. Bacterial endospores are the most resistant conventional microorganisms, which is why biological indicators contain spores. If a process kills a high population of resistant spores, it kills the less resistant forms as well. Only prions rank above spores in resistance.
Why not A: Vegetative bacteria are among the easiest microorganisms to kill and say little about the strength of a process.
Why not C: Enveloped viruses are the least resistant group because their lipid coat is easily damaged by chemicals and heat.
Why not D: Yeasts are fungi and are killed far more easily than spores.
Exam tactic: Biological indicators use spores because spores are the toughest living challenge.
Answer: C. Creutzfeldt-Jakob disease is caused by a prion, an abnormally folded protein that contains no nucleic acid. Prions are more resistant to standard disinfection and sterilization than any other infectious agent, so instruments from high-risk tissue such as brain need special handling per facility policy and IFU.
Why not A: Prions are not fungi and do not form spores.
Why not B: A prion is not a virus at all, so it has no viral genome or capsid to describe.
Why not D: Prions are not bacteria and do not live inside cells as organisms.
Exam tactic: Prion = protein only, top of the resistance ladder, above spores.
Answer: A. Biofilm is a community of microorganisms embedded in a protective slimy matrix that sticks to surfaces, especially inside lumens. Dried soil and biofilm are very hard to remove and protect organisms from disinfectants and sterilants. Keeping soiled items moist and cleaning them promptly helps prevent this.
Why not B: Spores never turn into prions. They are completely different agents.
Why not C: Drying does not sterilize. Dried soil protects organisms and makes cleaning harder.
Why not D: Viruses cannot multiply outside a living host cell.
Exam tactic: Dry soil plus time equals biofilm. Keep it moist, clean it fast.
Answer: B. The chain of infection has six links: an infectious agent, a reservoir where it lives, a portal of exit, a mode of transmission, a portal of entry, and a susceptible host. Breaking any one link stops the spread of infection. Sterile processing breaks the chain mainly at the transmission link by making devices safe.
Why not A: These are mixed infection terms, but they are not the six links. A carrier is a type of reservoir, a fomite and a vector are vehicles of transmission, and an antibody is part of host defense.
Why not C: This describes the course of an illness in one person, not how infection spreads.
Why not D: This is the instrument reprocessing cycle, not the chain of infection.
Exam tactic: ARE MPS: Agent, Reservoir, Exit, Mode, Portal of entry, Susceptible host.
Answer: D. Indirect contact occurs when organisms move from one person to another by way of a contaminated object, called a fomite. A poorly reprocessed instrument is a classic fomite. This is the mode of transmission that sterile processing exists to prevent.
Why not A: Airborne transmission involves tiny particles that stay suspended in air, not a contaminated instrument.
Why not B: Vector-borne transmission involves living carriers such as mosquitoes or ticks.
Why not C: Droplet transmission involves large respiratory droplets that travel a short distance.
Exam tactic: Contaminated object in between = indirect contact, the object is a fomite.
Answer: C. Bioburden is the population of viable microorganisms on or in an item before it is sterilized. Sterilization processes are validated for a certain challenge, so a high bioburden or leftover soil can overwhelm the process. Cleaning removes most of the bioburden and is the most important step in reprocessing.
Why not A: Detergent residue is a cleaning problem, but it is not what bioburden measures.
Why not B: Tray weight is a packaging concern and has nothing to do with microorganisms.
Why not D: Exposure time is a cycle parameter, not a measure of contamination.
Exam tactic: Bio = life, burden = load. Bioburden is the bug load before sterilization.
Answer: B. The Gram stain sorts bacteria by cell wall structure. Gram-positive bacteria have a thick peptidoglycan layer that holds the crystal violet dye and appear purple. Gram-negative bacteria have a thin layer plus an outer membrane and appear pink or red.
Why not A: Pink staining with a thin wall describes gram-negative bacteria.
Why not C: The Gram stain is a bacterial test. Viruses are too small and lack the cell wall it detects.
Why not D: Fungi such as yeasts can take up the Gram stain, so this statement is false, and a gram-positive report describes a purple organism with a thick wall.
Exam tactic: Positive = Purple. Both start with P.
Answer: D. Cocci are round bacteria. The prefix staphylo means bunch of grapes, so staphylococci grow in clusters. Staphylococcus aureus, including MRSA, is a leading cause of surgical site infections.
Why not A: Streptococci are round bacteria arranged in chains, not clusters.
Why not B: Bacilli are rod-shaped, not round.
Why not C: Spirochetes are spiral-shaped bacteria.
Exam tactic: Staph = grapes (clusters), Strep = string (chains).
Answer: C. An obligate anaerobe is harmed by oxygen and grows only where oxygen is absent. C. difficile survives outside the body by forming spores, which is why it persists on surfaces and resists many disinfectants.
Why not A: An obligate aerobe requires oxygen to grow, the opposite of this organism.
Why not B: A facultative anaerobe grows with or without oxygen.
Why not D: A microaerophile needs a small amount of oxygen, so it still uses oxygen.
Exam tactic: An = without. Anaerobe = lives without air.
Answer: A. Most human pathogens grow best with moisture, a food source such as blood or tissue, a near neutral pH, and temperatures close to body temperature. Soiled instruments left wet with organic matter offer all of these, so prompt cleaning denies organisms what they need.
Why not B: High heat and extreme pH damage or kill most vegetative bacteria.
Why not C: Freezing and lack of nutrients slow or stop bacterial growth.
Why not D: Sunlight, dryness, and disinfectants all work against bacterial growth.
Exam tactic: Bugs like what we like: warm, wet, and well fed.
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