I.W. Stewart

Performance of bioaerosol samplers used by the UK biotechnology industry

Abstract The quantitative assessment of bioaerosols is important in a number of industrial and health-care applications. Measurements to aid the control of airborne infection in hospitals, detection of the release of potentially harmful microorganisms from bio-processing equipment and monitoring the exposure of workers and animals to bioaerosols are examples of situations where different concentrations of microorganisms and varying ambient conditions may be expected. Microorganisms are notoriously difficult to assess accurately under such variable conditions and no single assay method is suitable for all applications; rather the method needs to be tailored to the application of interest. Problems are compounded by the differences in assay method (such as the type of media used for culturable counts) or sampler type selected, making the interpretation of the results difficult. An understanding of the airborne behaviour of microorganisms over a range of environmental conditions is vital if procedures are to be defined and recommended for the handling, sampling and assessment of bioaerosols. Microorganisms that are robust over a wide range of conditions are ideal as tracer particles. Unfortunately, the large majority of non-fungal bioaerosols are susceptible to damage. A predictable sampling procedure is required which will not affect the viability of the collected sample. Studies, reported on the development of procedures to characterise airborne biological particles, included tests carried out under controlled environmental conditions to compare the performance of five industrially important bioaerosol samplers with that of a reference glass wet-walled, cyclone sampler, using test aerosols of Saccharomyces cerevisiae cells and Penicillium expansum spores. The samplers tested were Andersen Microbial Sampler, Biotest RCS, Biotest RCS Plus, MicroBio MB1, and MicroBio MB2. The cyclone sampler, Andersen Microbial Sampler and the MicroBio MB1 and MB2 meet the basic criteria for a suitable reference sampler, except that the last three systems do not provide total counts. It will be important to investigate in the future how well they perform under the challenge of “real-life” conditions.

Evaluation of a model for the detection of aerosol-containing protease in real-time using chromogenic substrates in the sampling fluid of a cyclone and a bubbler

Abstract A model previously developed for predicting the colour change in a liquid sampler containing a chromogenic substrate was tested for the detection of aerosols of the protease enzyme, alcalase. Aerosols were generated in a bioaerosol test chamber at 20°C and relative humidity of 40%. The detection system responded to changes in alcalase concentration in real time. The performance of a high flow rate Aerojet cyclone was contrasted with that of a low flow rate bubbler. The model was tested with both a constant aerosol concentration and also with the sudden release of an aerosol for a short time. It was found that the model needed correcting for fluid loss from both samplers. The model predicted the performance of the bubbler better than the cyclone. Possible reasons are discussed.

Monitoring of hazardous biochemicals in the work-place atmosphere

Abstract Regulatory bodies are increasingly expressing an interest in the monitoring of the work-place air for hazardous biochemicals but examples in the literature of this form of monitoring are not common. In contrast, there are many examples of sensitive assays being developed for the quantitation of very small quantities of biochemicals in fluids which use a multi-step process. An aerosol sensing system has two components: an aerosol collection device and the biochemical detector. The coupling of the two has rarely been investigated. The requirements for such a sensing system are reviewed, together with an appraisal of the types of detector devices that might be suitable. It is suggested that there is a need to develop one-step sensitive sensors for real-time aerosol monitoring.

Procedures for the characterisation of bioaerosol particles. Part I: aerosolisation and recovery agent effects

The sampling and assay of bioaerosols are important ina number of industrial and health-care applications. Airborne microorganisms are notoriously difficult toenumerate accurately under such conditions and nosingle procedure is suitable for all applications. Problems are compounded by the differences in assaymethod or sampler type selected, making theinterpretation of results difficult.Understanding the airborne behaviour of microorganismsover a range of environmental conditions is vital ifprocedures are to be defined and recommended for theassessment of bioaerosols. Microorganisms that arerobust over a wide range of conditions are ideal astracer particles. Unfortunately, the large majorityof non-fungal bioaerosols are susceptible to damage. A predictable assessment procedure is required whichwill not affect the viability of the collectedsample.This paper examines how aerosolisation may affect the characteristics of two speciesof microorganism (Pseudomonas fluorescens andMS2 coliphage). It forms part of a larger programmeto develop standards for the assessment of biologicalparticles. The aim of the work was to develop procedures toexamine the effects of aerosolisation onmicroorganisms, with particular reference topre-aerosolisation protocol (spray suspension age) andpost-sampling handling protocol (aerosol age incollection solution). These procedures were then usedto examine the effect of recovery agents, addedto the spray suspension prior to aerosolisation, onthe culturability of E.coli.Aerosolisation reduces the culturability of P. fluorescensand the viability of viability of MS2coliphage. Pre-sampling and post-collection handlingand storage of these aerosolised microorganisms werealso found to have an effect. This and earlierstudies have shown that the culturable fraction ofmicroorganisms can be affected by the same factorsdescribed above. Of five microorganisms tested so farin the main programme, only Penicillium expansumspores were shown to be robust and stable with aconstant culturable fraction. Therefore, recommendinga particular microorganism (apart from P. expansum) as an airborne biological standard foraerosol studies is not advised. It is recommendedthat a microorganism, representative of the envisagedapplication, be characterised it in terms of theaerosolisation parameters, storage time and conditionsin the manner reported in this study. This can beachieved using the experimental equipment described.The addition of 0.1 mM concentrations of the sugarsinositol, trehalose and raffinose to spray suspensionsof Escherichia coli, prior to aerosolisation,made no significant difference to the culturablefraction of the aerosol.