Abstract
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RODAC Plating as an Indicator of MTB Contamination: Closure of the Risk Assessment Cycle
As biosafety professionals, we are called on to assist in the process of risk assessment, and we know intellectually that this is a cycle—it does not end when controls and personal protective equipment are identified and put into place. We know that a process of monitoring and evaluating should be in place to determine whether the mitigating measures were sufficient to abate the risk. However, this part of the process is often the most challenging, the one where we find ourselves without measurable metrics, technical ability, or resources.
Recognizing these limitations with respect to the ability to verify that their biosafety level 3 practices and procedures were indeed sufficient to contain Mycobacterium tuberculosis (MTB), Daneau et al 1 adapted and validated a common and easily deployable methodology for detecting viable microorganisms on solid surfaces. Using Replicate Organism Detection and Counting (RODAC)—plates containing media specifically designed to support the lengthy generation time of MTB while inhibiting growth of environmental contaminants—the authors demonstrated recovery of MTB at rates comparable to those reported in the literature for other microorganisms. The authors then applied this validated method following real-time drug susceptibility testing work in an active MTB laboratory. For 30 days, the authors used the modified RODAC plating technique to sample distinct points after one of their technicians performed drug susceptibility testing manipulations for MTB. A total of 201 samples were obtained from the technicians’ double-gloved little finger (used to manipulate the test tube cap), their gowned forearms and thighs, the armrest area of the biological safety cabinet, and the caps of the inoculated MTB culture tubes. Five of these samples produced MTB colonies, 2 of which were from the forearm and the thigh.
The authors take great care to communicate that their MTB laboratory is modern, International Organization for Standardization 15189 accredited, and staffed with highly trained technicians. They describe their analysis of the data and how it prompted (1) retraining of the staff, (2) use of additional personal protective equipment that reinforces removal of outer gloves inside the biological safety cabinet, and (3) the acquisition of a custom (closed-front) Class II biological safety cabinet. With this method, they have a tool to continue the process of risk assessment, evaluating if these new enhancements further reduce the possibility of laboratory contamination with MTB.
Additionally, the authors used this study as an opportunity to evaluate the efficacy of 70% ethanol on MTB. During the validation study, the researchers applied 70% ethanol to suspensions of Mycobacterium bovis bacillus Calmette-Guerin strain dried on glass microscope slides. The slides were then stamped with the RODAC plates after 5 or 60 minutes of contact time. While a reduction in the number of recoverable viable bacteria was noted, both time points failed to completely inactivate the mycobacteria, indicating that 70% ethanol is not an effective disinfectant choice for an MTB laboratory.
This report and others like it add to the foundation of applied biosafety knowledge and provide not just data but also examples that biosafety professionals and investigators can use in the process of risk assessment and as an aid in hazard awareness. This research is also directly translatable from the modern International Organization for Standardization-accredited laboratory to areas with limited resources, as the methodology is simple and inexpensive. The methods can be adapted to validate a risk assessment, to troubleshoot contamination issues, or even to evaluate the likelihood that a particular process might have led to a laboratory-acquired infection. Additionally, this article itself can be used as a training aid, a template for similar research in other fields, and a reminder to select for appropriate disinfectant.