Slit sampler

Decker, H.M. Wilson, M.E. A slit sampler for collecting airborne microorganisms. Appl. Environ. Microbiol. 1954, 2, 267-269. 

However, more meaningful data can be obtained if force rather than gravity is used to collect airborne particles. A stream of air can be directed onto the surface of a nutrient agar plate (impaction slit sampler) or bubbled through an appropriate buffer or culture medium (liquid impingement). Various commercial impactor samplers are available. Filtration sampling, where the air is passed through a porous membrane, which is then cultured, can also be used. 

For experimental evaluation of potential air disinfectants, bacterial or fungal airborne suspensions can be created in a closed chamber, and then exposed to the disinfectant, which may be in the form of radiation, chemical vapour or aerosol. The airborne microbial population is then sampled at regular intervals using an appropriate forced-air apparatus such as the slit sampler. With viruses, the air can be bubbled through a suitable liquid medium, which is then subjected to some appropriate virological assay system. In all cases, problems arise in producing a suitable airborne microbial suspension and in neutralizing residual disinfectant, which may remain in the air. 

Aseptic manipulations must be carried out in the grade A air of a laminar flow cabinet. Speed, accuracy and economy of movement are essential features of good aseptic technique. It is therefore essential that workers are well trained and motivated and familiar with the task in hand. Observation and microbiological monitoring of the operator and of the environment are very important. Air quality is measured using settle plates or slit samplers, work surfaces by taking swabs or by use of contact plates (Chapter 20). 

The performance of the RCS Plus Sampler was compared with that of the Casella slit sampler in a special facility providing a controlled environment by Benbough et Parallel samples were taken in the small environmental room (about 28 m ) into which test aerosols of controlled... 

Figure 13.12 Efficiency of the Biotest RCS Plus sampler for collection of spores in various size of particles compared to the Casella slit sampler (Reproduced by permission of Blackwell...

Figure 13.13 (a) Microbial aerosol produced by disc bowl centrifugation and subsequent removal of cell paste measured by the Cherwell SAS sampler (b) microbial aerosol produced by disc bowl centrifugation and subsequent removal cell paste measured by the Casell slit sampler operating over the same period as in Figure 13.13 (a). 

Bourdillon, R.B., Lidwell, O.M. and Thomas, J.C. (1941). A slit sampler for collecting and counting airborne bacteria. Journal of Hygiene Camb., 41, 197-224. 

This technique has several deflciencies. First, slit samplers do not separate and differentiate the size of airborne particles. Second, between the vacuum action and the rotating plate, the medium often dehydrates which can lead to poor bacterial growth and reduction in the viable count of stress-sensitive microorganisms. Third, the collected air sample is not a true representation of the air quality since about 10% of total particles are not deposited on the impaction medium. Lastly, only large particles with sufficient inertia will deviate from the streamlines and impact onto the agar surface. Small particles (<0.5 pm) miss the agar surface and are ejected back into the atmosphere. 

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