Performing viral assays in a BSL-4 laboratory is more involved compared to work in a BSL-2 laboratory due to required additional safety precautions. Here, we present an overview of practices and procedures used inside a BSL-4 laboratory illustrating proper Class II biosafety cabinet usage, waste management/disposal, and sample removal.
Work in a biosafety level 4 (BSL-4) containment laboratory requires time and great attention to detail. The same work that is done in a BSL-2 laboratory with non-high-consequence pathogens will take significantly longer in a BSL-4 setting. This increased time requirement is due to a multitude of factors that are aimed at protecting the researcher from laboratory-acquired infections, the work environment from potential contamination and the local community from possible release of high-consequence pathogens. Inside the laboratory, movement is restricted due to air hoses attached to the mandatory full-body safety suits. In addition, disinfection of every item that is removed from Class II biosafety cabinets (BSCs) is required. Laboratory specialists must be trained in the practices of the BSL-4 laboratory and must show high proficiency in the skills they are performing. The focus of this article is to outline proper procedures and techniques to ensure laboratory biosafety and experimental accuracy using a standard viral plaque assay as an example procedure. In particular, proper techniques to work safely in a BSL-4 environment when performing an experiment will be visually emphasized. These techniques include: setting up a Class II BSC for experiments, proper cleaning of the Class II BSC when finished working, waste management and safe disposal of waste generated inside a BSL-4 laboratory, and the removal of inactivated samples from inside a BSL-4 laboratory to the BSL-2 laboratory.
As safety of laboratory personnel handling high-consequence pathogens (no infection prophylaxes nor treatment options exist) is paramount, the US Department of Health and Human Services has established guidelines for facility construction and best practices for the safe conduct of work with pathogens in biomedical and clinical laboratories from a biosafety perspective1. Through legislation and regulation, many of the practices and procedures have become mandatory requirements that must be followed for work with these pathogens. In the US, pathogens that are easily transmitted from person to person, result in high case-fatality rates, and/or have the potential for major public health impact and bioterrorism, are categorized as National Institute of Health/National Institute of Allergy and Infectious Disease (NIH/NIAID) Priority A Pathogens and or Centers for Disease Control and Prevention (CDC) Bioterrorism Category A Agents2. In addition, high-consequence pathogens are classified as Tier 1 Select Agents if these pathogens are potential bioterrorism agents, have potential for mass casualties or devastating effects to the economy, critical infrastructure, or public confidence3.
BSL-4 operations, including access to institutes with BSL-4 laboratories, are more highly controlled than BSL-2/3 operations. For instance, it is substantially more difficult to gain access to a BSL-4 laboratory compared to a BSL-2 or BSL-3 laboratory due to substantial suit training requirements, extensive mentorship requirements, and additional medical biosafety prerequisites. In addition, there are typically more physical security barriers in a BSL-4 facility versus a BSL-2 or BSL-3 facility4-6. As outlined in our first article on BSL-4 entry and exit procedures, laboratory staff undergo extensive training and psychological screening to qualify for entrance into the BSL-4 laboratory7. Within the BSL-4 laboratory, risk of infection and mistakes are avoided or mitigated by following established procedures. Research must proceed carefully and deliberately, with minimal multitasking or distractions. Bending over in positive pressure suits is difficult, and the face shield may restrict procedures such as microscopy. Bulky gloves impede the performance of fine motor tasks, such as handling small items or labeling tubes. To minimize time spent in BSL-4 laboratories, laboratory specialists should review work procedures to identify steps that can be done ahead in a BSL-2 laboratory and then transport these materials into the BSL-4 laboratory for completion of the task(s). When removing materials for further processing in BSL-2 laboratory, materials are fixed and removed from the BSL-4 laboratory in a sealed secondary container. Examples of samples that may need to be removed include: fixed plates or tubes of infected material that will be analyzed by enzyme-linked immunosorbent assay (ELISA), immunofluorescence assay (IFA), or polymerase chain reaction (PCR).
In addition to greater physical limitations imposed by personal protective equipment required in BSL-4 laboratories compared to those in BSL-2 laboratories, procedures for inactivation of high-consequence pathogens in cell culture plates and waste disposal are stricter than those needed for less pathogenic viruses studied in a BSL-2 laboratory. At a minimum, these methods should meet CDC requirement. For example, contaminated cell culture plates and other materials can be inactivated with chemical reagents, such as neutral-buffered formalin. Treated cell culture plates or tubes are to be placed into heat seal pouches containing formalin and removed from the laboratory via a dunk tank filled with a liquid disinfectant. Waste buckets filled with disinfectant solutions and spray disinfectants are used for temporarily receiving waste generated during the experiment and for disinfecting gloves, cleaning biosafety cabinet surfaces and instruments, respectively. Quaternary ammonium disinfectant solution at the concentration listed is considered the gold standard for all US BSL-4 laboratories (Barr J, personal communication, 2015). Solid waste from a waste bucket is autoclaved to eliminate potential for contamination.
In an effort to visually demonstrate the workflow and limitations of general BSL-4 procedures, we used a standard viral plaque assay as an example of a commonly used viral procedure. While the viral assay procedure is described in general, we stress the biosafety procedures used to ensure safety of laboratory personnel in this protocol. Please refer to previous classical plaque assay visualizations for additional background on the plaque assay technique8,9.
The procedures presented here follow the BMBL specifications outlined by CDC1. However, the presented protocols are specific to the IRF-Frederick. Each BSL-4 facility has different standard operating procedures (SOPs) and methods of operation that impact the execution of experiments within the BSL-4 laboratory. Alternative procedures for waste stream management and execution of plaque assays may differ based on the management and operation of these laboratories. Nevertheless, a general understanding of the setup of a BSL-4 suit laboratory and procedures for performing work with Class II cabinets inside the BSL-4 environment will help scientists understand the constraints and safety implications when contemplating studies of high risk pathogens. Increased awareness of outside collaborators of the difficulties surrounding work in a BSL-4 laboratory can lead to adjusted expectations and greater ease in developing medical countermeasures in the research community.
1. Laboratory Entry
2. Preparation of a Class II Biosafety Cabinet in the BSL-4 Laboratory
3. Example: Plaque Assay
4. Waste Disposal and Cleaning of the Instruments and Biosafety Cabinet
5. Autoclaving Waste
6. Example: Fixing and Staining of Plaque Assays
7. Removing Samples from the BSL-4 Laboratory
Following proper procedures within the BSL-4 laboratory are critical for ensuring safe and effective completion of assays. By referring to the completed daily internal checklist (Figure 1), laboratory staff ensure that equipment is fully operational. Proper body positioning in the center of the BSC ensures that the experiment is performed under optimum air flow conditions (Figure 2). The virus sample is serially diluted to obtain plates that have 30-300 plaques per plate (Figure 3A) and to determine virus titer (Figure 3B). A number of factors affect formation of plaques, including virus tropism for host cell lines, inoculation technique, conditions for virus growth, appropriate dilution range, and overlay selection8. Waste generated in the BSC during the procedure is properly disinfected prior to removal from the BSC and again by autoclaving prior to leaving the BSL-4 environment. By following these procedures, no laboratory-acquired infections have been recorded during BSL-4 research at the IRF-Frederick.
Figure 1: Sample daily internal systems checklist. Daily completion of this checklist ensures that laboratory staff has checked equipment within the laboratory (most importantly the BSC) prior to initiating work. If the BSC is found to be outside of the calibrated range, this BSC must not be used, and maintenance should be notified. All BSCs must be properly calibrated and functioning. Please click here to view a larger version of this figure.
Figure 2: Back and side view of a laboratory specialist pipetting samples in a Class II biosafety cabinet. (A) Waste bucket containing yellow disinfectant solution and used pipettes are to the right of the well plates (B), and the disinfectant spray bottle is to the right of the waste bucket (A). Please click here to view a larger version of this figure.
Figure 3: Calculation of viral titer of sample. Viral titer is expressed as plaque forming units (pfu) per ml. To calculate the viral titer, count the number of clearly defined plaques (pfu) and divide by the product of the dilution factor (d) times the volume of diluted virus added to the well (V). Please click here to view a larger version of this figure.
Work in a BSL-4 laboratory requires considerable time and additional attention to detail. Any type of work in this environment requires well trained, thorough, and conscientious individuals. The standard viral plaque assay provides an accurate model of a common procedure for working with high-consequence pathogens in the BSL-4 laboratory, as the assay involves several major concepts in which laboratory workers must be trained.
The first major concept is the proper use and application of safe practices in Class II BSC, which functions as primary containment for high-consequence pathogens. Understanding of how a Class II BSC functions will dictate practices that greatly limit exposure risks to individuals. Work flow from a clean area ("clean side") to a contaminated area ("dirty side") across the work zone in the Class II BSC also helps to avoid cross contamination11. Clean and contaminated materials and supplies should be segregated to limit the movement of contaminated items over clean items.
The second major concept is physical and biological waste management. Proper steps in disposing both types of waste are essential in ensuring that the laboratory specialists stays safe and the environment is not contaminated. Steps during an experiment are designed to inactivate and destroy pathogens before samples are brought out of BSL-4 laboratory. Examples of such critical steps include: pipetting disinfectant into each tip, allowing at least a 10 min contact time of potentially contaminated materials with disinfectants, autoclaving waste, and validating sterility during autoclave cycles. These steps are designed to be redundant to ensure destruction of high-consequence pathogens.
The authors have nothing to disclose.
The content of this publication does not necessarily reflect the views or policies of the US Department of Health and Human Services (DHHS) or of the institutions and companies affiliated with the authors. This work was funded in part through Battelle Memorial Institute’s prime contract with the US National Institute of Allergy and Infectious Diseases (NIAID) under Contract No. HHSN272200700016I. M.R.H., D.P., L.B., K.J. and J.W. performed this work as employees of Battelle Memorial Institute. Subcontractors to Battelle Memorial Institute who performed this work are: S.M. as an employee of MRI Global; M.G.L. as an employee of Lovelace Respiratory Research Institute, Inc.; and J.H.K. as an employee of Tunnell Government Services, Inc.
Micro-Chem Plus | National Chemical Laboratories | 255 | |
Ethanol | Fisher | BP2818500 | |
2-ml 96-Deep Well Plates | Fisher | 278743 | |
10-ml Serological Pipette | Fisher | 13-678-11E | |
25-ml Serological Pipette | Fisher | 13-678-11 | |
6-well plates | Fisher | 140675 | |
Crystal Violet | Sigma | HT90132-1L | |
10% Neutral Buffered Formalin | Fisher | 22-050-105 | |
Tragacanth | Fisher | 50-702-2000 | |
20-μl Pipette Tips | Fisher | 21-402-550 | |
200-μl Pipette Tips | Fisher | 21-402-561 | |
1000-μl Pipette Tips | Fisher | 21-402-581 | |
DMEM | Lonza | 12-604Q | |
FBS | Sigma | F2442-500mL | |
Penicillin/Streptomycin | Lonza | 17-602E | |
2X EMEM | Quality Biological | 115-073-101 | |
Pipettor | Drummond | 4-000-101 | |
1000-μl Pipette | Rainin | L-1000XLS+ | |
200-μl Pipette | Rainin | L-200XLS+ | |
12-Well, Multichannel 200-μl Pipettor | Rainin | L12-200XLS+ | |
8-Well, Multichannel 1000-μl Pipettor | Rainin | LA8-1200XLS | |
Attest | Express Medical Supplies | MMM12192 | |
Autoclave | Getinge | GEB 2404 AMB-2 | |
Autoclave Bag | Fisher | 01-828E | |
2000-ml Beaker | Fisher | 02-591-10H | |
Autoclave Tray | Fisher | 13-359-20B | |
Pipette Tray | Fisher | 13-361-5 | |
37°C Incubator | Fisher | WU-39321-00 | |
Biohazard Can | Rubbermaid Commercial | FG614500 RED | |
Autoclave Tape | Fisher | 15-903 | |
Autoclave Rod | Made by IRF Facility | N/A | |
Light Box | Fisher | S11552 | |
Heat Sealer | Fisher | NC9793612 | |
Heat Seal Pouches | Fisher | 01-812-25H | |
Biohazard Bag | Fisher | 01-828E |