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OBJECTIVE

Apply the techniques of bacterial count using the pour plate and the spread platemethods.

Calculate the cell numbers in CFU/ml (colony forming units).INTRODUCTION

Aerobic organisms thrive at oxygen levels greater than 5 percent (fresh air is approximately 21

percent oxygen). They are the preferred microorganisms for composting because they provide

the most rapid and effective breakdown or organic materials. Anaerobes thrive when the compost

pile is oxygen deficient--referred to as an anaerobic condition.

Anaerobic microorganisms: Anaerobic microorganisms are undesirable in a compost pile

because they create unpleasant odors. Anaerobic processes can generate acids and alcohols that

are harmful to plants.

Aerobic microorganisms: Among all the microorganisms at work in a compost pile, the aerobic

bacteria are the most important initiators of decomposition and temperature increase in the

compost pile.

A pour plate is an alternative method for using agar plates to obtain isolatedcolonies. Pour platesare used when it is necessary to know the number oforganisms present per unit volume ofspecimen or other sample. When a specificaliquot is placed in the Petri dish, a count of thecolonies that grow afterincubation reveals their concentration in the original sample. Pour platesareused commonly in the bacteriologic examination of milk, or could also be used todeterminewhether sufficient bacterial numbers are present in urine samples tosignify the patient has aurinary tract infection. The number of bacteria insolution can be readily quantified by using thespread plate technique. In thistechnique, the sample is appropriately diluted and a small aliquottransferredto an agar plate. The bacteria are then distributed evenly over the surface by aspecialstreaking technique. After colonies are grown, they are counted and thenumber of bacteria in theoriginal sample calculated. Streaking in thistechnique is done using a bent glass rod. 0.1 mL ofbacterial suspension isplaced in the center of the plate using a sterile pipet. The glass rod issterilized by first dipping it into a 70% alcohol solution and then passing itquickly through theBunsen burner flame. The burning alcohol sterilizes the rodat a cooler temperature than holdingthe rod in the burner flame thus reducingthe chance of you burning your fingers. When all thealcohol has burned off andthe rod has air-cooled, streak the rod back and forth across the plateworkingup and down several times. Unlike streaking for isolation, you want to backtrackmanytimes in order to distribute the bacteria as evenly as possible. Turn theplate 90 degrees andrepeat the side to side, up and down streaking. Turn theplate 45 degrees and streak a third time.Do not sterilize the glass rod betweenplate turnings. Cover the plate and wait several minutesbefore turning itupside down for incubation. This will allow the broth to soak into the plate sothe bacteria won't drip onto the plate lid.

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RESULTS

DISCUSSION

CONCLUSION

REFERENCES