1. A PRELIMINARY STUDY ON THE COLONIZATION TREND OF MICROORGANISMS IN DECOMPOSING RATS TO DETERMINE
POST MORTEM INTERVAL
Suganya Kanagarethinam Paul*, Sarimie Nizam and Anita Zara Weinheimer
Faculty of Health and Life Sciences, Management & Science University, Shah Alam, Selangor Darul Ehsan, Malaysia.
Determining post mortem interval (PMI) has been a critical issue faced in the field of forensics thus new methodologies have to be introduced to be able to obtain a
more accurate PMI. This study aims to study the trend of bacterial colonization in decomposing rats of different manner of death to correlate to the post mortem interval
(PMI). A study was conducted by collecting oral swab from decomposing Sprague Dawley rats at five hours before death and consequent intervals after death up till
the end stage of decomposition. Swab collections were analyzed by using the conventional bacteriologic culture and identification method together with a comparison
to 0.8C of MacFarland Standard solution to determine the closest turbidity followed by sub-culturing of individualized pure colonies on Blood agar and MacConkey agar
to isolate gram positive and gram negative bacteria. The average of Colony Forming Unit (CFU) counts were used to plot graph that showed the peak of colonization
trend at 41 hours which relates to active degradation stage in which the microorganism involved in decomposition are at a very rapid stage of growth. Morphological
characteristics of isolated colonies were observed and categorized to their specific types which showed most colonies appeared to be of α-hemolysis and Non-Lactose
fermenters. The colonization trend of microorganisms showed the growth pattern of microorganisms that correlated with the physical stage of decomposition hence
preliminarily being able to determine the time that has elapsed since death. Also, the morphological structure of the colonies were able to preliminarily determine the
type of bacteria that are possibly contributing in the process of decomposition.
General objectives
To study the growth rate of microorganisms in
decomposing rats of different manner of death to
correlate to the post mortem interval (PMI).
Specific objectives
1.To observe the colonization rate of two isolated
colonies according to its manner of death
2.To observe the colonization rate of pure colonies
and enumeration of pure colonies on differential
agar.
The colonization activity of microorganisms in the
decomposing Sprague Dawley rats correlates with
the post mortem interval (PMI)
ABSTRACT
OBJECTIVES
HYPOTHESIS
INTRODUCTION
RESULTS
Graph 1 : Colonization trend of microorganisms is
plotted based on the average of Colony-Forming
Unit (CFU) count. Peak colonization was observed
at 41st hour (active decay stage). At this stage,
rapid decomposition that took place had high
amount of microorganisms colonizing due to the
shift from anaerobic to aerobic bacteria. Body that
ruptures releases foul smelling gasses and attracts
the presence of arthropods as well as many other
external factors that speeds up the decomposition
rate. It also attracts a lot of aerobic bacteria to help
in the decomposition, hence the shift from anaero-
bic to aerobic (Evans, 1963). This gives a direct
comparison to the colonization that takes place at
5 hours after death in which it explains that most
pre-existing aerobic bacteria in the body dies due
to shortage of oxygen and is going through a shift
into anaerobic bacteria that will be helping in de-
composition. The fluctuation in the growth pattern is
influenced by the presence of chemical
(Chloroform) and environmental factors (Fry et al,
1972).
Graph 2 shows the individual colonization of the
two isolated pure colonies regardless of it being
cultured on Blood Agar of MacConkey agar. Colony
A shows a higher rate of colonization which draws
into a conclusion that Colony A is the most influen-
tial bacteria that is helping in decomposition from
the beginning till the end . Colony A is the most via-
ble bacteria it is well supported by the nutrients pro-
vided in the body to help in decomposition as com-
pared to Colony B.
Graph 3 shows that most colonization is highly
supported by the Blood Agar as the nutrients in the
Blood Agar provides a ambient condition for the
growth of the bacteria. Bacteria hemolysis the red
blood cell and appears to be either an alpha-
hemolytic cell, beta-hemolytic cell or gamma hemo-
lytic cell. MacConkey plates also showed a consid-
erable amount of colonization which derives the
bacteria growing to be either a lactose fermenter or
a non lactose fermenter (Elllen M.E., 2013).
DISCUSSION
Hypothesis is accepted. The results shows that
colonization of microorganisms correlated with the
PMI. Also, different manner of death showed a
different growth rate pattern due to the individuality
of microorganisms present in each sample. The
presence of foreign material in the body also
influences the growth rate pattern as it inhibited the
growth of microorganisms in the poisoning manner
of death. Lastly, environmental factors plays an
important role in Diptera colonization.
CONCLUSION
Byard, R. W., & Tsokos, M. (2013). The challenges presented
by decomposition. Forensic Science, Medicine and
Pathology, 9,135- 137.
Rogers, C. J. Dating Death : Forensic Taphonomy and the
Postmortem Interval Thesis submitted for the Degree
of Doctor of Philosophy.
VanLaerhoven, S. L., & Anderson, G. S. (1999). Insect
succession on buried carrion in two biogeoclimatic
zones of British Columbia. Journal of forensic
sciences, 44(1), 32-43.
REFERENCES
METHODOLOGY
Graph 1
Graph 2
Graph 3
Determining Post Mortem Interval (PMI) is a
crucial issue faced in the field of forensics. A PMI
determination by a pathologist turns out to be
more troublesome and less precise with the
progression of time and delicate tissue
decomposition (VanLaerhoven & Anderson,
1999). A related study had been done on
microbiological analysis to correlate
decompositional changes with time in order to
develop alternative methodologies (Rogers,
2010). Decomposition is a complex process
comprising several stages of degradation which
are initiated immediately upon the death of an
organism (Byard & Tsokos, 2013). After death,
the human body will ordinarily decay in a specific
foreseeable style and the changes occurring can
be typically be partitioned into various different
stages; fresh, bloat, decay, post-decay and dry
or skeletal. Every stage is additionally
connected with a rough estimation of time period
which is likely to happen, subject to the factors
that can change these time periods. The starting
breakdown of tissue is due to autolysis and the
activity of bacteria present in the tissues. As the
tissues breakdown continues, interior
microorganisms mainly from the gastrointestinal
tract spread to different parts of the body to
further the decomposition process (Janaway et
al., 2009). From a research done on bacterial
community structure of a cadaver, it was
recorded that there was a shift in aerobic
bacteria to anaerobic bacteria. The exact
estimation of the post mortem interval is very
critical to the successful completion of death
examinations. Thus, the microorganism activity
that takes place in the body of decomposing
carcasses would serve as an alternative
methodology to study the time that has elapsed
since death. This is due to the presence of
microorganisms in the decomposing bodies
before the presence of any insects of larvae.