mcb 150 exer 3
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Transcript of mcb 150 exer 3
MICROORGANISMS
K C C A P U L O N G | Z H E R R E R A | K D I N F A N T E
I C P A C I A | J P S E V I L L A
M C B 1 5 0 M I C R O B I A L E C O L O G Y
AIRIN
N
OBJECTIVES:
• Identify different microorganisms present in the air;
• Understand and demonstrate the sedimentation procedures, the gravity plate method and impingement technique;
• Compare the number and types of airborne microorganisms present in the intramural and extramural environments;
• Learn to compute for the determination of the microbial load present in the air using the formulas given.
GRAVITY PLATE METHOD• also called as settle plate
method
• plates were exposed in the assigned areas for 15 minutes
• microorganisms were collected by sedimentation or by gravity to deposit air particles (microorganisms) on the plates
ADVANTAGES
inexpensive and easily performed
very useful for directly monitoring airborne contamination of specific surfaces
Useful for qualitative analysis of airborne microorganisms
very limited since this method is only capable of monitoring viable biological particles that sediment into air and settle at time of exposure
it will not detect smaller particles or droplets suspended in the air and it cannot sample specific volumes of air
vulnerable to interference and contamination from non-airborne sources and growth medium might deteriorate if exposed for too long
microorganisms may easily become overgrown in heavily contaminated conditions
DISADVANTAGES
The laboratory is the area expected to have the most number of microorganisms since microorganisms in
air are most likely to spread in areas where pathogens are handled for research purpose (Pepper et al.,
2014).
IMPINGEMENT METHOD
When air is dispersed in the liquid, particles in the air are trapped.
The usual volume of collection medium is 20 mL and the typical sampling duration is approximately 20 minutes which prevents evaporation during the sampling of warm climates or freezing of the liquid medium when sampling at lower temperatures.
Quantification of airborne microorganisms is accomplished by plating the collection fluid.
A suitable collecting medium for liquid impingement samplers must preserve the viability of the microorganism while inhibiting its multiplication.
ADVANTAGES
gives quantitative results where sample volume can be calculated using the flow rate and sampling timemore accurate representation of present microorganisms in air will be obtained
DISADVANTAGES
the technique may damage some microbial cells and affect viability
no particle size discrimination which prevents accurate characterization of the sizes of the airborne particles that are collected, and at overlong sampling times it allow multiplication of cells in the liquid medium
DISCUSSIONS
More bacterial air spores grew on PCA compared to that of the NA plate mainly because PCA has glucose, making it richer in terms of nutrient content and carbon source. (In samples obtained from lab and rooftop).
The glass beads acted as dispersants. They were used to prevent bubble formation which could have affected the microbial cell diffusion. It breaks aggregates of microorganisms thus uniformly releasing them into the solution and further trap the microorganisms in the solution because of its pores.
RESULTS
SITE IMPINGEMENT TECHNIQUE GRAVITY PLATE METHOD
bacteria (PCA) fungi (PDA) NA bacteria(PCA)
fungi(PDA)
100 10-1 100 10-1
Lab 21,68 52,81 0,1 1,1 58,55 68,29 0,4
Street 86,121 122,60 1,3 2,0 50,49 32,28 5,13
Rooftop 86,144 65,spreader
2,0 1,0 17,15 26,34 1,3
Table 3.1. Bacterial and fungal counts recorded from air sampled in different environments.
Table 3.2. Computed microbial load (cfu / ft3 air) for the various environments sampled.
* sampling time= 20 mins; ft3 of air sampled = 7.1429; Vi= 50mL
SITE cfu / mL of impingement liquid
cfu / ft3 air*
bacteria fungi bacteria fungi
Lab 1.68 x 10^3 <100 ESPC 1.18 X 10^4 <700
Street 1.77 x 10^3 <100 ESPC 1.24 X 10^4 <700
Rooftop 1.40 x 10^3 <100 ESPC 9.80 x 10^3 <700
RESULTS
Table 3.3. Cultural and morphological characteristics of predominant bacteria and fungi present in air sampled from different environments.
SITE DOMINANT BACTERIA DOMINANT FUNGI
cultural(PCA)
microscopic(OIO)
cultural(PDA)
microscopic(HPO)
Lab Circular, white, flat, entire margination
G(-), cocci cottony, circular, white
filamentous
Street White colony (spreader), opaque
G(-), long rods, in chains
Green mold, cottony, compact
conidia borne on a vesicle, septate, possibly Aspergillus
Rooftop circular, entire margin, flat, yellow-pigmented colony
G(+), circular shape
a) cottony, filamentous form and margin, white
club-shaped conidiophore, septate, possibly Aspergillus
RESULTS
COMPUTATIONS
cfu / ft3 air
Given:
sampling time = 20min
capacity of limiting orifice = 10 L / min
volume of impingement liquid after sampling = 50mL
Number of liters per sample = [sampling time (in minutes)] x [capacity of limiting orifice]
= 20min x 10 L / min
= 200 L
Cubic feet of air sample = liters of sample / 28
= 200 L / 28
= 7. 1429 ft3
FOR BACTERIA
CFU per cubic feet of air =
N= CFU/ml of impingement
Vi = 50ml
Va = 7. 1429 ft3
= 1.18
= 1.24
= 9
Laboratory
Street
Rooftop
FOR FUNGI
𝐶𝐹𝑈𝑐𝑢𝑏𝑖𝑐 𝑓𝑒𝑒𝑡 𝑜𝑓 𝑎𝑖𝑟
=¿100(50𝑚𝑙 )7.1429 ft 3
¿<700
𝐶𝐹𝑈=¿100𝐸𝑆𝑃𝐶
REFERENCES
Compendium of Methods for the Microbiological Examination of Foods (Frances Pouch Downes, Keith Ito) American Public Health Association, Apr 1, 2001
Food Quality Magazine: Air Sampling 101. Judie Buddemeyer. June/July 2005 issue. http://www.foodquality.com/details/article/878155/Air_Sampling_101.html?tzcheck=1
Pepper, I.L., Gerba, C.P. and Gentry, T.J. 2014. Environmental Microbiology. 3rd edition. Londom: Elsevier Inc.