1.1 Microbiology Fundamentals for Central Service
Key Takeaways
- Microorganisms include bacteria, viruses, fungi, protozoa, and prions — each with different characteristics and resistance levels
- Bacteria are classified as gram-positive or gram-negative based on their cell wall structure and staining characteristics
- Bacterial spores (endospores) are the most resistant form of microbial life and require sterilization to destroy
- Viruses require a host cell to replicate and range from easily killed (enveloped) to highly resistant (non-enveloped)
- Fungi include yeasts and molds; they can cause opportunistic infections in immunocompromised patients
- Prions are misfolded proteins that cause fatal neurological diseases (CJD) and cannot be destroyed by standard sterilization
- Biofilm is a community of microorganisms that adhere to surfaces and produce a protective matrix, making them extremely difficult to remove
- Understanding microbial resistance levels is essential for selecting the correct reprocessing method
Microbiology Fundamentals for Central Service
Understanding microbiology is the scientific foundation of everything Central Service technicians do. Every cleaning, disinfection, and sterilization process is designed to eliminate or reduce microorganisms to safe levels. Without understanding what you are fighting, you cannot fight it effectively.
Types of Microorganisms
1. Bacteria
Bacteria are single-celled organisms that can survive independently. They are classified by:
- Shape: Cocci (round), bacilli (rod), spirilla (spiral)
- Gram stain: Gram-positive (thick cell wall, stains purple) vs. gram-negative (thin cell wall with outer membrane, stains pink)
- Oxygen requirement: Aerobic (needs oxygen), anaerobic (grows without oxygen), facultative (either)
- Spore formation: Some bacteria (Bacillus, Clostridium) form endospores — dormant, highly resistant survival structures
Key bacteria in healthcare:
| Organism | Type | Significance |
|---|---|---|
| Staphylococcus aureus (MRSA) | Gram-positive coccus | Leading cause of surgical site infections |
| Clostridioides difficile (C. diff) | Gram-positive, spore-forming | Healthcare-associated diarrhea; spores resist many disinfectants |
| Pseudomonas aeruginosa | Gram-negative bacillus | Thrives in moist environments; biofilm former |
| Escherichia coli | Gram-negative bacillus | Indicator organism for contamination |
| Mycobacterium tuberculosis | Acid-fast bacillus | Resistant to many disinfectants; requires special protocols |
2. Viruses
Viruses are obligate intracellular parasites — they cannot replicate without a host cell.
- Enveloped viruses (HIV, Hepatitis B, influenza): Surrounded by a lipid envelope; easier to kill with disinfectants
- Non-enveloped viruses (norovirus, adenovirus): No lipid envelope; more resistant to disinfection
Key viruses in healthcare:
| Virus | Type | Concern |
|---|---|---|
| Hepatitis B (HBV) | Enveloped, DNA | Bloodborne; survives on surfaces for 7+ days |
| Hepatitis C (HCV) | Enveloped, RNA | Bloodborne; major occupational exposure risk |
| HIV | Enveloped, RNA | Bloodborne; relatively fragile outside the body |
| Norovirus | Non-enveloped, RNA | Environmental contamination; difficult to kill |
3. Fungi
Fungi include yeasts (single-celled) and molds (multicellular with hyphae).
- Cause opportunistic infections in immunocompromised patients
- Examples: Candida albicans (yeast), Aspergillus (mold)
- Fungal spores are moderately resistant to disinfection
4. Protozoa
Protozoa are single-celled organisms that can form protective cysts.
- Cryptosporidium cysts are resistant to standard chlorine disinfection
- Less commonly encountered in CS but important in water quality discussions
5. Prions
Prions are misfolded proteins — not living organisms — that cause transmissible spongiform encephalopathies (TSEs):
- Creutzfeldt-Jakob Disease (CJD) is the most relevant to CS
- Prions are NOT destroyed by standard steam sterilization, EtO, hydrogen peroxide, or radiation
- Special reprocessing protocols are required for suspected prion-contaminated instruments:
- Immerse in 1N sodium hydroxide (NaOH) for 1 hour, then steam sterilize at 270°F (132°C) in a gravity displacement cycle for 1 hour
- OR use a prevacuum sterilizer at 275°F (134°C) for 18 minutes after NaOH soak
- Single-use instruments may be preferred for high-risk procedures
Biofilm — The Hidden Danger
Biofilm is a structured community of microorganisms enclosed in a self-produced extracellular polymeric substance (EPS) matrix that adheres to surfaces.
Why Biofilm Matters in CS:
- Forms within minutes to hours after contamination
- Is 1,000–1,500 times more resistant to antimicrobials than free-floating (planktonic) bacteria
- Standard cleaning and sterilization may not penetrate mature biofilm
- Commonly forms in lumens, channels, hinges, and crevices of surgical instruments
Preventing Biofilm Formation:
- Point-of-use treatment — keep instruments moist and wipe off gross soil immediately after use
- Prompt transport to decontamination (do not allow instruments to dry with soil)
- Thorough cleaning before disinfection or sterilization
- Enzymatic detergents break down organic matter that feeds biofilm
Remember: You cannot sterilize a dirty instrument. Cleaning is the most critical step in reprocessing because sterilization cannot penetrate biofilm or dried organic matter.
Order of Microbial Resistance (Most to Least Resistant)
Understanding resistance levels guides reprocessing decisions:
| Level | Organism Type | Killed By |
|---|---|---|
| Most resistant | Prions | Special protocols (NaOH + extended steam) |
| ↑ | Bacterial spores (Bacillus, Clostridium) | Sterilization only |
| ↑ | Mycobacteria (TB) | High-level disinfection or sterilization |
| ↑ | Non-enveloped viruses (norovirus) | Intermediate to high-level disinfection |
| ↑ | Fungi | Intermediate-level disinfection |
| ↑ | Vegetative bacteria (Staph, Strep, E. coli) | Low to intermediate-level disinfection |
| Least resistant | Enveloped viruses (HIV, HBV) | Low-level disinfection |
This hierarchy is sometimes called the "hierarchy of microbial resistance" and is fundamental to understanding why different reprocessing methods exist.
Which type of microorganism is the MOST resistant to standard sterilization methods?
Biofilm on surgical instruments is dangerous because:
Which of the following bacteria is gram-positive, spore-forming, and a leading cause of healthcare-associated diarrhea?
The single most important step in preventing biofilm formation on surgical instruments is: