Establishing a Microbiotherapy Laboratory: Best Practices for Zoning and Physical Isolation

I. Basic Zoning Definitions (General classification; adjustable for BSL-2/BSL-3 requirements)

Microbial therapy laboratories are typically zoned as follows: Clean Zone → Buffer Zone → Semi-contaminated Zone → Contaminated Zone.

Clean Zone (Clean Area / Non-contaminated Area)

Offices, primary changing rooms, break rooms, document rooms, reagent storage (unopened raw materials/excipients), and central control rooms; free of live bacteria and experimental samples.

Buffer Zone (Pressure transition and airtight isolation core)

Secondary changing rooms, airlocks, pass-through boxes, and disinfection buffer rooms; serve as physical barriers between zones, managing pressure differentials and the disinfection/sterilization of personnel and materials.

Semi-contaminated Zone (Transition Zone)

Corridors, preparation rooms, culture medium preparation areas, and equipment cleaning/pre-treatment areas; involves potential contact with contaminants but no open handling of live bacteria.

Contaminated Zone (Core experimental area; high risk)

Microbial inoculation, anaerobic culture, live bacteria expansion, sample isolation, live bacterial product dispensing, and positive control operations; involves the presence of live bacterial aerosols and contaminated samples.

Strict Principles: Direct connection between clean and contaminated areas is prohibited; all movement between zones must pass through buffer/isolation areas; separate pathways for personnel, materials, and waste must be established to prevent cross-flow.

II. Physical Isolation Measures for Zoning (Clean vs. Contaminated)

1. Physical isolation via enclosure structures (Primary barrier)

Continuous, airtight sealing of walls, ceilings, and floors.

Clean zones utilize prefabricated color steel panels (50mm/75mm) with coved corners to eliminate dead spaces; joints are fully sealed with neutral silicone sealant to prevent aerosol penetration.

Walls in contaminated zones extend up to the structural slab to prevent air communication via the ceiling plenum; wall penetrations for utilities are strictly prohibited unless airtight seals are applied at the penetration points.

Flooring consists of self-leveling epoxy or polyurethane; seamless and impermeable to prevent leakage and cross-contamination of bacterial fluids between zones. Door Isolation Requirements

No direct interconnecting doors between clean and contaminated zones; airlock buffer rooms are mandatory.

Doors must open towards the area of ​​higher contamination (Clean Zone ← Semi-contaminated Zone ← Contaminated Zone).

Airtight doors with automatic closers (kept normally closed) are recommended for high-risk contaminated zones; interlocking doors are preferred (preventing simultaneous opening of both doors in the airlock).

Strictly prohibited: Windows in experimental areas opening directly to the outside; shared passageways between clean and contaminated zones.

2. Pressure Differential Gradient Isolation (Physical air isolation—critical)

Utilize controlled pressure differentials to prevent contaminated air from backflowing into clean zones; standard gradient:

Clean Zone (+10 to +15 Pa) > Semi-contaminated Zone (+5 to +10 Pa) > Buffer Airlock > Contaminated Zone (0 Pa or negative pressure of -5 to -10 Pa; negative pressure recommended for open-bench handling of live microorganisms).

Live microorganism handling rooms (contaminated zones) should be designed with relative negative pressure to prevent the outward spread of bio-aerosols.

Airlock pressure differentials must fall between those of the adjacent zones to act as a buffer/barrier.

Independent ventilation systems: Separate Air Handling Units (AHUs) for supply and exhaust in clean and contaminated zones; no ductwork interconnection. Exhaust air from contaminated zones must pass through HEPA filters before high-level discharge; direct discharge or recirculation to clean zones is prohibited.

Install real-time pressure monitoring and alarm systems to provide timely warnings of pressure imbalances, preventing cross-contamination caused by air backflow.

3. Material Flow Isolation: Unidirectional transfer; no crossing paths

Clean Material Pathway

Raw materials/auxiliaries & sterile consumables → Clean Zone → Buffer Transfer Hatch → Contaminated Zone

Transfer hatch requirements: UV disinfection, interlocking mechanism, and independent controls for both sides (clean side vs. contaminated side); arbitrary bidirectional transfer is prohibited. Independent Waste Route (Contaminated Material Flow)

Contaminated samples, waste bacterial cultures, and contaminated consumables: Contaminated Area → Waste Buffer Room → Autoclave Room → External Removal Exit

✅ Optimal Solution: Completely separate the waste exit from the personnel entrance to create an independent waste corridor;

❌ Prohibited: Transporting laboratory waste or unsterilized items through the clean zone via the main personnel corridor.

Contaminated equipment must not be moved back into the clean zone; all items removed from the contaminated zone must be sterilized first.

4. Personnel Flow Isolation: Unidirectional personnel movement and mandatory changing/buffering

Standard Unidirectional Personnel Flow:

Outside → First Change (remove street clothes) → Clean Corridor → Second Change (don cleanroom attire) → Buffer Air-lock → Semi-contaminated Zone → Contaminated Experimental Zone

Exit Flow:

Contaminated Zone → Disinfection Buffer → Undressing/Cleanroom Attire Removal Buffer → Shower (optional for high-level BSL) → First Change → Outside

Key Points:

Separate changing areas for clean and contaminated zones; no shared changing rooms;

Personnel are not permitted to return directly from the contaminated zone to the clean zone; they must pass through undressing and disinfection buffer stages;

Clearly mark flow directions with arrows and install physical barriers or partitions to prevent shortcuts or counter-flow.

III. Isolation Measures for Wastewater, Exhaust Air, and Solid Waste

Wastewater Isolation

Collect experimental wastewater from the contaminated zone separately; sterilize in situ before discharging into the drainage network; strictly prohibit interconnection between clean and contaminated drainage networks; install independent sewage piping where conditions permit.

Physical Zoning for Solid Waste Storage

Use lidded autoclave bags within the contaminated zone for immediate sealing at the source; temporarily store waste in the waste buffer room; do not stack contaminated waste in the clean zone.

Equipment Isolation

Designate specific equipment (pipettes, centrifuges, incubators, etc.) for specific zones; do not move clean-zone equipment into the contaminated zone; do not move contaminated-zone equipment to the clean zone without prior sterilization. IV. Common Errors in Floor Layout

❌ Clean office door opens directly into the live-bacteria laboratory;

❌ Absence of pass-through boxes; personnel transport samples directly across zones;

❌ Zoning indicated only by floor markings, lacking physical wall partitions;

❌ Shared ventilation systems; air recirculated from contaminated zones;

❌ Personnel corridors also used for waste transport;

❌ Buffer rooms serve merely as passageways, lacking interlocking doors or disinfection capabilities.

V. GMP / Biosafety System Management Requirements

Create and archive flow diagrams for personnel, materials, waste, and airflow for use during acceptance inspections;

Develop cross-zone operational SOPs specifying procedures for material transfer and entry/exit;

Conduct periodic airtightness testing, pressure differential verification, and containment structure leak testing;

Use zone-specific workwear and tools, employing color-coding for zone management.

VI. Recommendations for Streamlined Implementation

Prioritize floor layout: separate the two ends—one for clean personnel entry and the other for waste exit;

Install dedicated negative-pressure airlocks for high-risk live-bacteria handling rooms;

Ensure continuous airtightness of the containment structure; seal all openings for air ducts and utility lines;

Ensure unidirectional flow (no backflow) for air, personnel, materials, and waste;

Use independent ventilation systems for different zones; treat exhaust air from contaminated areas with HEPA filtration.