microbiology: practical competence...

Julia Hughes

HNC/D Animal Studies

Module: Microbiology

~ ~

Microbiology: Practical Competence

Introduction Infectious diseases in animals are caused by the invasion of tissues by bacteria,

especially the epithelium, by microorganisms. This invasion have many effects which

can be detrimental to the animals health, let alone be passed on to other animals

through physical contact, aerosol, contamination of water or by being transmitted

through a parasite such as the common flea.

Prevention by vaccination, good hygiene, quarantine or culling is the best way of

reducing and eliminating bacterial infections however it may be necessary to treat the

infection with antibiotic and antibacterial drugs. These drugs help alleviate the

symptoms together with the use of anti-inflammatory or analgesic drugs, rest and

good nutrition.

Viruses and bacteria are prokaryotes, simple structures that lacking well-defined

nuclei and membrane-bound organelles and their own metabolism (see figure 1

below). They are all obligate parasites on plants or animal cells, hijacking the cells

metabolism in order to produce more of the virus that continue to reproduce until the

cell ruptures.

FSU: 2009

Julia Hughes



~ ~

There are several different ways to test for bacteria in a laboratory format. Some

culture types of which include:-

Steak

Spread

Pour

Slope

Stab

Broth

Membrane

The growth rate will vary according to condition in temperature. A rise of 10% will

double the growth rate and E-coli doubles every 20 minutes at body temperature.

Culture Tests with Micrococcus Luteus

Micrococcus Luteus is gram positive, generally a non-pathogenic bacteria (but may be

opportunistic in immunosuppressed individuals) and mainly considered a

contaminant. It primarily habitats the normal flora of the mammalian skin, human

mouth, mucosae, oropharynx and upper respiratory tract but can also be found in dust,

air, water and soil.

Results of Laboratory Testing Several experiments were performed using this bacteria as follows. In these

experiments a nutrient agar or a meat extract, have been used.

Preparation of a Petri Dish

1. The nutrient agar is warmed up and kept in a warm water bath, preferably at

body temperature to keep the culture from solidifying.

2. An empty sterile Petri Dish was opened slightly and quickly had the nutrient

agar poured into it in order to cover the bottom and fill the dish to

approximately one third.

3. The dish is labeled with initials, date and contents of Nutrient Agar.

4. The nutrient is then left to set and can be used for experimenting.

Contamination of a Petri Dish

1. The lid of a pre-prepared Petri Dish was removed and left open to the room air

for 10 minutes.

2. The lid was then replaced and the dish was stored at room temperature

overnight.

On examination the following day, it was found that within the 10 minute exposure to

air, the nutrient agar had become contaminated. This result confirms the fact that

there is air-borne but non-harmful bacteria in normal air that is breathed every day.

Julia Hughes



~ ~

A Streak Test

1. Prepare the area first by cleaning down the surfaces with 100% alcohol

solution.

2. Put a Bunsen burner on full flame to pull up the air around it and kill off any

bacteria within the vicinity.

3. Sterilise a loop in a high flame.

4. Take the lid off a slope agar with the bacteria Micrococcus Luteus, flame the

top of the bottle and then quench the heat of the loop first in the agar.

5. Scrap a tiny amount of bacteria from the slope, put the lid back on and sweep

the sample lightly three times across the top, three times down the side and

then three times along the bottom of the agar in the Petri dish, keeping the lid

as low down as possible to avoid any unnecessary contamination.

6. Reposition the lid of the Petri dish.

7. Reflame the loop to kill off any remaining bacteria.

8. The Petri dish is then turned upside down for labeling with initials, date and

sample name of M Luteus Streak and placed in a warm area of 37oC

overnight.

The result of this test showed viable cells of bacteria growing in all three of the

streaked areas (see photograph).

A Lawn Test


solution.




4. Take the lid off a slope agar with the bacteria Micrococcus Luteus, flame the

top of the bottle and then quench the heat of the loop first in the agar.

5. Scrap a tiny amount of bacteria from the slope, put the lid back on and drop

the sample gently onto the agar in the Petri dish. Reflame the loop to kill off

any remaining bacteria.

6. Take a swab out of its packet and spread the bacteria evenly all over the agar,

keeping the lid as low down as possible to avoid any unnecessary

contamination.




sample name of M Luteus Lawn and placed in a warm area of 37oC overnight.

The result of this test showed viable cells of bacteria growing all over the agar (see

photograph).

Julia Hughes



~ ~

An Antibiotic Test


solution.



3. Put some alcohol in a beaker.


5. Take the lid off a slope agar with the bacteria Micrococcus Luteus and quench

the heat of the loop first in the agar.

6. Scrap a tiny amount of bacteria from the slope, put the lid back on and drop

the sample gently onto the agar in the Petri dish. Reflame the loop to kill off

any remaining bacteria.

7. Take a swab out of its packet and spread the bacteria evenly all over the agar,

keeping the lid as low down as possible to avoid any unnecessary

contamination.



10. Put some tweezers in the beaker with the alcohol.

11. Pick up an antibiotic disc with the tweezers and lay it on the agar lawn.


sample name of M Luteus Antibiotic and placed in a warm area of 37oC

overnight.

The result of this test was inclusive but should have shown which of the antibiotic

discs had the greater affect of ensure that the bacteria did not grow. Where the

antibiotic had no effect whatsoever, large growths of bacteria would have grown

around and under that particular disc.

Another test was performed and the results are shown in the photographs attached.

Working from the top disc results show as follows:-

“FC” - Fusidic Acid – some intermittent clearing of bacteria

“OX” – Oxacillin – no bacteria cleared

“NO” – Novobiocin – bacteria very noticeable around the disc

“PG” – Penicillin G – no change with bacteria growth steady

“S” – Streptomycin – virtually total clearance of bacteria

“T” – Tetracycline – localize intense clearing of bacteria

“C” – Chloramphenicol – a wide clearing of bacteria

“E” – Erythromycin - a large clearing of bacteria

These results shows that while Fusidic Acid, Tetracycline and Chloramphenicol have

an effect on Micrococcus Luteus, Streptomycin and Erythromycin are the most

efficient in their anti-bacterial qualities.

Julia Hughes



~ ~

References

FSU, 2009, http://micro.magnet.fsu.edu/cells/bacteriacell.html, Molecular

Expressions, Bacterial Cell Structure

microbiology: practical competence...

Documents