A fellow student one that is not as careful as you finds the

A fellow student, one that is not as careful as you, finds the following: They have produced 2 plates of media, and inoculated each plate with three different bacterial samples. Unfortunately, they have labeled none of their plates. The plates have the following appearances: Plate 1 The media is a dark red (burgundy) color, 3 different bacteria were inoculated onto the plate and bacteria are growing in all 3 of the sections of the plate. Section A: you observe growth of bacteria with a translucent/clear region around all colonies. Section B: you observe growth with no change in the color of the media around all colonies. Section C: you observe growth with a greenish color around all colonies. Plate 2: The media is a pale purple color, 3 different bacteria were inoculated onto the plate, and organisms are growing in 2 of the sections of the plate. Section A: you observe no growth of bacteria at all. Section B: you observe bacterial growth with pink colonies. Section C: you observe bacterial growth with colorless/white colonies. Using the diagrams on the next page, COMPLETELY interpret these results-this means I want to know what enzymes are active. First tell me what media are represented for each plate, what the media\'s properties are (selective, differential, any pH indicators), whether the media is selective and/or differential. Second fully interpret the type organisms that are present in each of the three sections of each plate, including enzymes, and whether the bacteria is Gram positive or Gram negative.

Solution

Answer:

Plate 1: The dark red colour media is Eosine-methylene blue (EMB) agar due to the presence of methylene blue and eosine dye. It is a selective and differencial culture medium. It is used for selective growth of gram negative bacteria and differentiate the growth of lactose fermenting and lactose non-fermenting coliforms. The details is given below:

Lactose fermenter

E. coli

Explaination: In the presence of an acidic environment (low pH) after the fermentation of lactose, EMB forms a complex that precipitates out onto the coliform colonies, producing dark centers and greenish sheen around the colonies. This reaction is characterstics of Escherichia Coli. In addition, other weaker fermentation of lactose results in colonies with a pinkish-purple color with no change around the colonies as their is low change of pH of growth medium. However, in absence of an acidic environment the dye is not absorbed. Thus, the colonies of lactose non-fermentors will be colorless.

Plate 2: The pale purple colour media is MacConkey agar due to the presence of crystal violet dye. It is a selective and differencial culture medium used for selective growth of gram negative bacteria and differentiate the growth of lactose fermenting and lactose non-fermenting coliforms. The details is given below:

Explaination: MacConkey agar is detect the growth of coliforms and enteric pathogens based on their ability to ferment lactose. Lactose fermenting coliform such as Escherichia Coli, produce pink colonies on this medium when ferment on differential ingradient of the medium i.e. lactose. And enteric bacteria that do not ferment lactose (enteric pathogens) produce colourless/white colonies. The dye in the culture medium, crystal violet act as selective ingradient to inhibit the growth of Gram-positive bacteria.

Sections	Colony appeared	Bacteria	Gram staining	Enzyme produced
A	Translucent/clear around all colonies	Lactose non-fermenter	Gram negative bacteria	no enzyme
B	No change of colour around the colonies	Poor lactose fermentor i.e. Enterobacter aerogens	Gram negative bacteria	Permease and Beta-galactosidase
C	Greenish colour around the colonies	Lactose fermenter E. coli	Gram negative bacteria	Permease and Beta-galactosidase