Aeromicrobiology- Aerosols-Bioaerosols-Assesment of air quality- Solid and Liquid impingement

1. Aero microbiology
The term aeromicrobiology was coined in the 1930s by F.C.Meier in relation with a project
concerned with study of life in air. Aeromicrobiology has been defined in various ways as
“the study of aerosolisation, aerial transmission, and deposition of biological materials” or
more specifically as “the study of diseases that may be transmitted via respiratory route” or
even more aptly as “the study of airborne organisms and their effects on human health and
the environment”.
Aeromicrobiology in its wider sense is the study of all forms of microbial life
in air. To an environmental microbiologist, aeromicrobiology is “the study of various aspects
of intramural (indoor) and extramural (outdoor) aeromicrobiology in relation with the
airborne transmission of environmentally relevant microorganisms including viruses,
bacteria, fungi, yeasts and protozoans”. Besides these microbes, other biological materials
like pollens, insect debris, animal debris, animal danders (chief source of allergic disorders)
are also found in air.
It is well known that airborne microbes are important pathogens causing diseases in plants,
animals and humans. These pathogens spread by aeromicrobiological pathway (AMB
pathway). Some of the important airborne human pathogens are as follows:
Diseases Pathogens
(a)Viral:
Influenza Influenza virus
Chickenpox Varicella virus
Smallpox Variola virus
Measles Rubeola virus
German measles Rubella virus
Dengue fever Flavivirus

2. (b) Bacteria:
Diphtheria Corynebacterium diphtheriae
Pertussis (whooping cough) Bordetella pertusis
Meningitis (meningococcal) Neisseria meningitidis
Tuberculosis Mycobacterium tuberculosis
Klebsiella pneumonia Klebsiella pneumoniae
Serratia pneumonia Serratia marcescens
Q fever Coxiella burnetii
Pneumococcal Streptococcus
Pneumonia Pneumoniae
Sterp throat Streptococcus
Scarlet fever Pyogenes
(c) Fungal:
Aspergillosis Aspergillus fumigates
Blastomycosis Blastomyces dermatidis
Coccidioidomycosis Coccidiodes immitis
Cryptococcosis Cryptococcus neoformans
Histoplasmosis Histoplasma capsulatum
(d)Protozoal:
Pneumocytosis Pneumocytosis carinii
Dropletnuclei:
Airborne droplet nuclei develop when the fluid of pathogenic droplets (1-5 µm in
size; micrometre = one-thousandth of a millimetre) evaporates. They are so small and light
they may remain suspended in the air for several hours. Thus, they may also infect persons
entering a room which has been left by a patient long ago. Also, airborne droplet nuclei can
be widely dispersed by air currents. Tuberculosis, chickenpox, measles and possibly also
influenza may be transmitted this way.

3. When investigating the origins of droplet and airborne infections, there are several
well-known primary sources of infectious particles. Vomiting, toilet flushing, sneezing,
coughing, and talking. Moreover, toilet bowls, the water in them, and toilet seats may harbor
infectious particles after the initial flush, making additional aerosolization of infectious
particles possible with additional flushes for as long as 30 minutes after the initial flush.
Particle desiccation, discussed above, is important in this context. A single sneeze, for
example, generates as many as 40,000 large droplet particles; most will desiccate
immediately into small, infectious droplet nuclei, with 80% of the particles being smaller
than 100 μm.
Droplet nuclei released from various activities
The transmission of infectious diseases via airborne or droplet routes may also depend
on the frequency of the initiating activity. For example, while a single sneeze may produce
more total infectious particles than a cough, Couch et al. reported that coughing is more
frequent than sneezing during infection with Coxsackievirus A. This finding suggests that
coughing is a more likely method of airborne transmission for this disease than sneezing. As
coughing is also a common symptom of influenza infection, it may also contribute to the
airborne transmission of this pathogen.Finally, infectious individuals are not always the
immediate source of airborne infectious particles. Many people spend considerable time in
office buildings, for example, and as a result become exposed to airborne pathogens that
originate from nonhuman sources (e.g., molds, toxins produced by molds, pollen, pet dander,
and pest droppings). The health effects associated with naturally occurring indoor biological
air pollutants include disease, toxicoses, and hypersensitivity (i.e., allergic) diseases. In
addition, exposure to indoor biological air pollutants has been associated with “sick building
syndrome,”a set of nonspecific symptoms that may include upper-respiratory symptoms,
headaches, fatigue, and rash and“appear to be linked to time spent in a building, but no
specific illness or cause can be identified.”
Bioaerosols:
A bioaerosol is an aerosol comprising particles of variable biological origin.The
term bioaerosol is used to describe living airborne particles or those originating form
living organisms. This can be fungal spores, pollen grains, endotoxins, or particles of
animal dander. Bioaerosols are complex mixtures consisting of several components that
can stem from simple organic molecules (dimensions in the nanometer range), viruses,

4. bacteria and bacterial spores, mold spores and hyphae, pollen (with diameters as small
as 100 micrometers), and animal and plant debris (of various sizes).
Relative Sizes of Bioaerosols
Bioaerosols vary considerably in size. Their composition depends on several
factors including the type of microbe or toxin, type of particles they are associated with
(as mist or dust), and the gases in which the bioaerosol is suspended.In general,
bioaerosols range from less than 0.01µm to more than 100µm in diameter and are
classified on the basis of their size into different modes as follows:
Mode type Size range (µm in diameter)
Nuclei Fine <0.1
Accumulation particles 0.1 to 2.0
Coarse >2.00
Bioaerosols in the respirable size range (≤10µm) are of particular concern to human
health.The composition of bioaerosols can be liquid or solid or a mixture of the two and
should be thought of as microorganisms associated with airborne particles or as airborne
particles containing microorganisms. It is rare to find microbes not associated with dust
or mist or other airborne particles in the atmosphere.
Assessmentof Air Quality:
Airborne bacterial and fungal cells and spores may be present in droplets as
bioaerosols, as very small individual particles that stay suspended for long periods, or as
larger clumps and aggregates that settle rapidly onto surfaces. They can be an important
source of infection in medical facilities and can contaminate sensitive manufacturing
operations, but regular monitoring of airborne microorganisms is sometimes neglected.
Bioaerosols containing airborne microbes can be controlled at every point of spread
launching, transport and deposition by using different mechanisms which include ventilation,
filtration, biocidal agents and isolation.

5. Air Sampling:
Bioaerosol sampling provides useful data that can be used for a variety of
applications, such as (i)measuring the presence and concentration of airborne
biocontaminants; (ii)confirming dissemination from a biocontaminant source; (iii)evalution
of bioaerosol exposure and health risks; (iv)documentation of clearance to reoccupy a space,
following remediation efforts; and (v)compliance monitoring in industrial environments. The
objective of bioaerosol sampling is the efficient removal and collection of biological particles
from the air in a manner that does not affect the integrity of the sample. This depends on the
characteristics of the microorganisms and on the physical features of the sampling
instrument. The selection of a sampler depends on a number of factors, such as sampler
performance, expected bioaerosol concentration, and the analysis method.
Sampling Devices and Equipment:
Various methods have been developed for the collection of bioaerosols.One can
choose any of these sampling methods depending upon the site of collection, environmental
conditions of sampling and mobility and sampling efficiency. Different kinds of samplers
have been designed,from the very simple type, such as the Andersen six stage impaction
sampler.Several types of samplers are commonly used,which are based on different methods
of sampling-impingement, impaction, centrifugation, filtration and deposition.
Impingement is the trapping of airborne particles in a liquid matrix;
Impaction is the forced deposition of airborne particles on a solid surface; Centrifugation is
the mechanically forced deposition of airborne particles using increased forces of gravity;
Filtration is the trapping of airborne particles by size exclusion, and Deposistion is the
collection of airborne particles using only naturally-occuring deposition forces.
Impaction:
Impaction is the forced deposition of airborne particles usually on a solid agar surface.
The impaction method uses the inertia of particles to separate them from the air. The particles
are deposited onto a collection surface, usually on agar medium for culture based analysis or
an adhesive coated surface for microscopic analysis. The impaction process depends on the
inertial properties of the particles, such as size, density and velocity and on the physical
parameters of the impactor such as inlet nozzle dimensions and air flow pathway. The
impactor sampler draws air through an inlet nozzle dimensions and air flow pathway. The
impactor sampler draws air through an inlet nozzle toward a collection surface, and particles
with sufficient inertia impact while smaller particles remain in the air stream.
Impator samplers may be designed with multiple circular inlet mozzles; the sampler is
then referred to as a multiple-hole or sieve sampler.If there are several stages with
successively smaller nozzles, the sampler is referred to as a cascade impactor. For samplers
in which air is drawn through a single nozzle, the shape of the nozzle is usually rectangular
and the impactor is reffered to as a slit sampler. Some impactors utilize centrifugal

6. impaction, which also uses inertial forces to separate the particles from the air stream, but in a
radial geometry.
1.Multiple-hole impactor samplers:
The Andersen six-stage impactor sampler
The Andersen impactor sampler has been widely used for culturable bioaerosol
measurements. The sampler draws air at a flow rate of 28.3 1/min and is operated using an
electric vaccum pump. The Andersen six-stage impactor sampler consists of six stages with
decreasing nozzle diameter that collect progressively samller particles onto agar plates.The
general operating principle is that the air is sucked through the sampling pore and strikes agar
plates.There are six petridishes containing suitable growth medium, kept under sieves of
different pore size.Each sieve has 400 pores.The circular orfice at the top sucks air at flow
rate of 28.3 1/min. passing it through the sieve arranged in gradually decreasing order of pore
size. Air impacting on last petridish goes out.Larger particles are collected on the first layer,
and each successive stage collects smaller and smaller particles by increasing the flow
velocity and consequently the impaction potential.Particles of similar size impact on a given
petridish only. In this way spores/pollens of six dimension orders are impacted on agar

7. surface of individual petridish. The number of colony-forming units (CFU) that form on the
agar collection plates provides bioaerosol size distribution information.
Slit Impactors:
Rotorod intermittent sampler Burkard personal multiple hole sampler
Slit impactors are available for the measurement of either culturable or total airborne
microorgamisms.Many slit impactors have a moving collection surface that allows
enumeration of bioaerosol concentration over time. Slit impactors that deposit the bioaerosol
onto an agar surface for the estimation of culturable cells include the Mattson-Garvin air
sampler and the Slit-to-agar sampler. Slit impactors that collect particles onto an adhesive-
coated surface are generally used for the microscopic enumeration of fungal spores or pollen
grains. These include the Burkard spore traps and the personal air sampler, the Air-O-Cell
sampling cassette,the Allergenco air sampler and the Rotorod intermittent sampler.
Burkard personal slide sampler, battery operated, suitable for indoor environment is
10cm high having a rectangular orfice at the top. The microslide is coated with glycerine
jelly. The sampler sucks air at flow rate of 10.0 1/min. through the orfice. The particles get
impacted on the slide forming a band. Slide is mounted and scanned.
The Rotorod sampler has an intermittent rotating impactor, is power-operated and
ideal for both indoor and outdoor studies. It is light weight portable sampler. It has arm that
holds two cubical rods coated with silicon grease.Unexposed rods remain folded. Arm has a
shield at top for protection from rains. Exposure time can be regulated.The rods are mounted
on a grooved slide in a basic Fuschin stain and Scanned.
Liquid Impingement:
Liquid impingement samplers draw air through an inlet and particles are collected in a
liquid. The particle is removed from the air by inertial force and impaction into a swirling or
bubbling liquid. Aggregates of cells may be broken apart by the action of the collection fluid.

8. The collection of bioaerosol particles over a wide range of airborne particle concentrations,
the ability to divide the sample for multiple analyses, and the option of applying a variety of
analysis methods. A liquid sample can be concentrated by filtration or diluted by liquid
addition, depending on the concentration of collected microorganisms. In addition, several
culture media can be inoculated with aliquots of the collection medium for the culture of
groups of microorganisms with different nutrient requirements.
(i)The AGI-30 all glass impinge sampler; (ii)The SKC Biosampler; (iii)TheBurkardmulti-stage liquidimpinge
The AGI-30 all-glass impinge sampler is a widely used sampler that has a curved inlet tube
designed to simulate the nasal passage,making this sampler useful for studying the respirating
infection potential of bioaersols. The air is transmitted through a liquid medium where the
particles are trapped. The sampler is usually run at 12.5 1/min. flow rate at a height of 1.5 m,
the average human breathing height. It is easy to use, inexpensive, portable, easily sterilized
and has good bioefficiency. It is very efficient for particles in the range of 0.8 to 15µm. The
usual volume of the collection medium is 20 ml and duration of sampling approximately 20
minutes. Sampling media may be a simple one as 0.85% NaCl, or more complex as 1%
peptone. Enriched or defined growth media can also be used for specific microbes.
The Burkard multi-stage liquid impinger is a stainless steel sampler that collects
particles in three size fractions: > 10µm, 4 to 10µm and < 4µm. The BioSampler collects
particles by drawing air through three nozzles that are directed at an angle toward the inner
sampler wall and the liquid swirls upward on the inner wall of the sampler to remove
collected particles. Although other impingers are designed for use with water-based
collection fluids, the Biosamplers can be used with viscous collection fluids (e.g., heavy
white mineral oil) to minimize sampling stress and evaporation loss of the collection buffer.