Chapter 5 Aeromicrobiology Ian L. Pepper and Scot E. Dowd 1. List

Chapter 5
Ian L. Pepper and Scot E. Dowd
List some beneficial microorganisms not described in the text that are spread via the
aeromicrobiological pathway.
Soil particulate material that routinely becomes aerosolized during high wind conditions also contains large
populations of aerosolized bacteria which are heterotrophic plate count (HPCs). The majority of
HPCs aerosolized are non-pathogenic and mimic the normal soil microflora. Therefore,
aerosolized HPCs are a mechanism for dispersing microbes spatially and enhancing diversity. As
an example this provides a mechanism for dispersion of biodegradative genes or nitrogen fixing
bacteria. In theory any beneficial microbe found in soil can become aerosolized.
Describe the AMB pathway for hantavirus including launching mechanisms, transportation
mechanisms, and deposition mechanisms.
Launching: wind
Transportation: wind
Deposition: gravitational settling; rain deposition
Give an example of a continuous linear source and an example of an instantaneous area source of
Continuous linear sources of bioaerosol = biosolid applicator moving across a field
Instantaneous area source of bioaerosol = endotoxin associated with soil particulates during a wind
gust across a field.
Considering a wind speed of 1.5 m/s, an object that is 12 cm tall, and normal air viscosity, determine
whether conditions around the object would be considered turbulent.
Conditions around the object would not be considered turbulent due to a low Reynolds Number
Consider an airborne virus and airborne protozoan with a radius of 30 mm and 1 μm and particle
densities of 2.0 and 1.1 g/cm3, respectively. Under normal gravitational acceleration
calculate the terminal velocity for each.
Use Stokes Law:
V 
D 2 x ( p  1 ) x g
18 
v = velocity of fall
g = acceleration of gravity (980 cm sec-2)
D = diameter of particle (cm)
ρp = density of particle g/cm3 = 2.0 for virus and 1.1 for protozoa
ρ1 = density of air
ζ = viscosity of air
Due to smaller size of virus, virus descends much more slowly than protozoa.
Calculate the annual community risk of infection given the following data: aerosolized virus
concentration = 7.16/cm3 of air, duration of exposure = 8h, infectivity constant r = 0.0253,
and breathing rate = 0.83 m3/h.
Probability of infection [per day = ρi = 1 - exp (-4N)
Where r = infectivity constant = 0.0253
N = number of pathogens inhaled per day
Here N 
7 .16 x 8
 69
∴ ρi = 1 - exp (-0.0253 x 69)
Annual risk = Pyear = 1 - (1 - ρi)d
Where d = 2 days
∴ Pyear = 1 - (1 - ρi)2
Pyear = 0.96
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