Identification of The Unknown Bacterium

Aim

Conclusion

Based on bacteria cell wall structures, they can be

classified into two main groups; Gram positive and Gram

negative.

Gram positive bacteria have a thick multi-layered

peptidoglycan component of the cell wall on the other hand;

gram negative bacteria have a single layer of peptidoglycan

component surrounded by an outer membrane containing

lipopolysaccharide. Bacteria exhibits various shapes and

sizes such as ;coccus(spherical),different cocci

arrangements (cluster ),bacillus(rod shape),a refractive

endospore within bacterium, peritrichous flagella.

Methodology

References

Results

To identify the unknown bacteria a combination of

selective and differential media, gram staining and

selected biochemical tests were conducted (LSC-10036

Microbiology labs 2014-2015).

Oxidase Test (OX)

Bacteria can be classified into aerobic and anaerobic. A

deep violet compound results from the oxidation of

tetramethyl-p-phenylenediamine dichydrochlorine by

aerobic bacteria. This indicates a positive result.

Catalase Test (CAT)

Some bacteria are able to produce catalase. Addition of

3%v/v hydrogen peroxide to a bacterial slope culture,

results an immediate bubbles production and indicates

catalase positive bacteria. LV Test

Gram positive bacteria can be differentiated based on their

ability to break down lecithovitellin. Around a ‘halo ‘like

opalescence produced by the positive bacteria colonies; egg

yolk due medium turbidity disappears.

1. Greenwood, D., Barer, M., Slack, R., (2012). Medical

microbiology. . 18th ed. China: Churchill Livingstone

Elsevier.

2. 2. Public Health England and National Health Service

(2014). UK Standards for Microbiology Investigations.

Catalase Test. London : National Health Service.

3. Singleton, P., Saintsbury, D. (1978). Dictionary of

Microbiology. Bath: John Wiley & Sons.

Bacterial Motility Test (MOT)

Some bacteria can exhibits surface flagellar motors.

Bacterial surface flagella enable chemotaxis, the

movement towards nutrients and away from toxins. Motile

bacteria show a positive result.

Carbohydrate Fermentation Test

Bacterial sugar fermentation results in acids and /or gas

production.

Glucose (GLU)- Change of colour from purple to yellow

indicates an acid production and therefore a positive

result.

Lactose (LAC) - The presence of brownish/orange colour

indicates very little acid production and therefore a positive

result.

Sucrose (SUC) - The presence of deep purple colour

indicates a negative result.

Mannitol (MAN)– Bubble production inside the Durham

tube indicates a gas formation and therefore a positive

result.

Gram Staining

Bacteria can be classified into; Gram positive and Gram

negative. Gram positive remains purple colour whereas

Gram negative bacteria change colour to pink. Staining

bacteria allows to microscopically determining bacterial

shape and size.

The results obtained from various biochemical tests were

compared with different bacterial properties given in

appendix Table 11 (LSC-10036 Microbiology labs 2014-

2015), part of which is presented below:

Eight out of nine properties were compatible with the

qualities of Bacillus cereus. Only catalase test was

unmatched and indicated that the unknown bacteria is

unable to produce catalase. On the contrary, in the appendix

table 11, it was stated that B. cereus has an ability to

produce enzyme in form of immediate enzyme-substrate

bubbles. According to Public Health England, the Oxidise

test should be conducted on colonies that are cultivated from

18 to 24hr. Organisms lose their catalase activity with age

and therefore a false negative result could be obtained

(Public Health England and National Health Service, 2014).

Introduction

The objective of this project was to identify unknown

bacteria from the set of nine different bacteria. The

purpose was to conduct various biochemical tests in order

to obtain biological properties underpinning bacterial

identification.