Getting Your FACS Straight by Christopher Pitoscia
Flow cytometry, particularly fluorescence-activated cell sorting, or FACS, is a laboratory technique that offers the ability to differentiate between homogeneously mixed cells based on various parameters or characteristics of interest, such as DNA content or protein expression. To accomplish this, FACS sorters suspend cells in a liquid and align them in a single-file stream by rapidly passing the liquid through a narrow opening in a vibrating mechanism. A beam of LASER light intersects with each cell in the stream as it passes through the opening, and the resulting light scatter is analyzed by complex optics. Based on the light scatter measurements, cells with the same characteristics are deflected into a designated collecting tube, thus sorting them into a pure sample for further analysis. Cell sorting by this mechanism has become practically ubiquitous in biomedical research laboratories, but it is not without safety concerns, especially when sorting unfixed human cells.
In 1997, the International Society for Analytical Cytology (ISAC) published a series of reports that remain the standard biosafety guidelines for the sorting of unfixed human cells. At a minimum, due to the potential for human tissue to harbor HIV, hepatitis C and other bloodborne infections, unfixed human cell specimens must always be treated as Biosafety Level 2 (BSL 2) materials- capable of transmitting infectious disease to healthy adult humans. See the CDC publication, Biosafety in Microbiological and Biomedical Laboratories www.cdc.gov/OD/OHS/biosfty/ bmbl5 / BMBL_5th_Edition.pdf
When sorting these samples, malfunctions of the cell sorting equipment in which the cell-liquid stream is deflected, or the stream-focusing nozzle becomes clogged, have the potential to create aerosols of the cell-liquid matrix that can spread potentially infectious materials considerable distances from the machine. The ISAC guidelines therefore recommend that sorters in which unfixed human cells will be processed be housed in a biosafety cabinet enclosure, and that sorting not be performed on the open bench. Furthermore, operators of sorters are directed to observe BSL-3 work practices when handling such materials. Additional training, testing, signage and access restrictions also apply to sorting activities involving unfixed human materials, and sorting operations involving lower-risk materials.
Simple Procedure Leads to a Painful Injury by Kevin McGhee
While many common procedures in a laboratory become simple to perform with experience, accidents can still occur while performing the most seemingly benign of tasks. Recently a lab worker was microwaving a small amount of agarose solution to prepare an electrophoresis gel. The researcher was quite experienced with the procedure, having performed it several hundred times by their own estimation, without incident. However, the worker, not anticipating that the neck of the bottle would be hot, attempted to retrieve it from the microwave by gripping it barehanded. Unfortunately, the neck of the bottle WAS hot, the worker reflexively dropped the bottle, and the superheated solution erupted from the container as it struck the lab bench, splashing onto the worker’s face and eyes.
The consequences were fortunately limited to minor first degree burns and irritated eyes, but several lessons are apparent from this incident. An eye injury would have been easily avoided had appropriate eye protection been worn. Insulated gloves were also available but were not used, as the worker assumed that grabbing the container by its neck would be an adequate shortcut. Both of these oversights were largely a result of the assumption that such a common task, with a relatively benign substance, would not be hazardous, obviating the need for personal protective equipment. In fact, the physical hazard posed by the hot surface of the container and the superheated agarose solution remained, but was momentarily disregarded due to the seemingly routine nature of the procedure.
Microwaving and autoclaving present a potential for a superheated liquid to erupt upon initial handling of a bottle or flask. To avoid this, allow sufficient time for the material to cool before touching the container and gently tap the container at arm’s length to ensure that any boil over does not contact your hand or arm.
Injuries can be quite common during everyday tasks, even for tasks as simple as cooking in one’s own kitchen or driving home from work. Very often accidents occur when tasks become so familiar that they are routine, and able to be performed without requiring much active thought. Because laboratories can present serious hazards, even for the most routine of tasks, laboratory workers must always take special care to perform even the most routine of procedures with appropriate precautions.