Question

What are four techniques of environmental surveillance developed by microbiologists to assess both the types and numbers of specific microbes present in specific environments?

Answer 1

A clean looking environment also consists numerous microbes causing contamination. The main sources of microbial contamination in a particular environment could be air, water, personnel, and surfaces (surfaces could be any surface that we come in contact on a regular basis). Therefore, the major objective of environment surveillance is to evaluate the type and number of viable living microbes in a particular controlled environment.

The four major techniques involved in environment monitoring are

1) Active air sampling

2) Passive air sampling

3) Surface sampling

4) Personnel samples

Active air sampling

Active air sampling involves use of volumetric air sampler. These samplers measure the number of microorganisms accumulated in a given volume of air or over a set time period in a microbial culture medium. Air samplers measure a defined quantity of air because motion of microbes depends upon presence of moisture in air, temperature, light, movement of air, due to which they are not evenly distributed in air. The volume of air measured is particularly one cubic meter and data is assessed in cfu/m3. After culturing microorganisms, staining is done to identify the type of microbes. Also various assays are performed such as microscopy, staining selective/differential, gram staining, cotton blue staining etc.

Passive air sampling

Passive air sampling involves use of settle plates like petri-plates. The petri-plates are filled with culture medium and are allowed to evaluate direct settling of any viable microorganism on it. The rate of settling depends on the attribute of the particles and flow of air. Larger microbes or particles will settle at a faster rate in comparison to smaller particles.

Surface sampling

Surface sampling is done using contact plates and swabs. The major advantage of this method is that it helps in monitoring the state of a particular environment and the potential risk of transference of microbial contamination in that particular area. The surfaces are evaluated using swabs. The swabs are rubbed over the surfaces by rotating 10-30 times and streaking the swab on a microbial culture plate or inoculating into a suitable microbial broth followed by incubating the plates and broth.

Surface contact plates are more common test for evaluating surface contamination. Following incubation, the assay provides information about the number of colonies. The data is quantified as the number of colony-forming units (cfu) per square centimeter.

Personnel samples

Personnel samples are assessed using finger plates and gown plates. It includes taking sample through swabs or contact plates from finger plates of glove hands, garment surfaces or sleeves. Sleeves, gowns samples are taken using contact plate method while finger plates are formed by taking finger impressions of both the hands on an agar or any other culture medium plate. The sample types are quantified as cfu per 25 cm2