A COMPUTER SIMULATION STUDY ON BIOAEROSOL COLONY COUNTING ERROR DUE TO MASKING EFFECT
Resource
ANNALS OF OCCUPATIONAL HYGIENE v.42 n.7 pp.501-510
Journal
ANNALS OF OCCUPATIONAL HYGIENE
Journal Volume
v.42
Journal Issue
n.7
Pages
501-510
Date Issued
1998
Date
1998
Author(s)
CHEN, CHIH-CHIEH
Abstract
The prevalence of bioaerosol particles has gained
significant attention in the past decades and is considered
to be a potential health hazard for people in a variety of
environments, To identify and quantify airborne
microorganisms, the bioaerosols are collected directly on
semisolid culture media, or trapped from air into liquid
substrates, followed by culturing, counting, and
identification of the resulting colony forming units,
Studies on error due to overcrowding of the colonies have
concluded that the bias did not become significant until
about 300 colonies/plate were present, but no study has
taken the non-homogeneity of colony size into account, In
the present study, a Cartesian coordinate system was used to
simulate the surface area of standard 100 mm diameter
colony culture plates and the colonies growing on them, A
resolution of 1000 x 1000 was found to be accurate enough to
represent the actual size of the colony, The capacity of
distinguishing overlapping colonies (defined as resolution
index) the covering fraction, the colony surface density,
and the colony size distribution were among the primary
parameters investigated in this study. The counting
efficiency was found to consistently decrease with
increasing surface density and decreasing resolution index,
The recommended upper Limit of colony counts on each plate
depended not only on the number concentration but also the
size distribution of the colonies. To have a minimum
counting efficiency of 95%, the colony densities should not
exceed 1290, 200 and 71 colonies/plate, for colony sizes of
2, 5 and 8 mm, respectively. This was based on the
assumption that the colony size was uniform and resolution
index was 0.8. As the geometric standard deviation (GSD)
kept increasing, the Larger GSDs resulted in higher covering
fraction, and thus, lower counting efficiency. This
phenomenon was independent of resolution index. (C) 1998
British Occupational Hygiene Society. Published by Elsevier
Science Ltd.
Subjects
AIRBORNE
Type
journal article