What is the total magnification when using a 10x eyepiece and a 40x objective lens?

The isolation streak plate technique is specifically designed to separate individual bacterial cells on the surface of an agar plate. By streaking a loop or swab across the agar in a systematic pattern, the bacterial population is progressively diluted, allowing single cells to land apart from each other. These isolated cells then grow into distinct colonies, which can be used for identification, further testing, or pure culture development. This technique is fundamental in microbiology for obtaining pure cultures from mixed bacterial samples, ensuring accurate study of bacterial morphology, physiology, and biochemical characteristics.

A. Strong lactose fermentation: Strong lactose fermenters, such as Escherichia coli, produce dark colonies with a metallic green sheen on eosin methylene blue (EMB) agar. This occurs because the fermentation of lactose produces acid, which interacts with the dyes in the medium, causing the characteristic coloration.

B. Partial lactose fermentation: Partial or weak lactose fermenters, like Enterobacter aerogenes, produce pink or purple colonies on EMB agar. The moderate acid production from lactose fermentation leads to less intense color change compared to strong fermenters.

C. Non-lactose fermentation: Colorless and translucent colonies on EMB agar indicate that the bacteria are non-lactose fermenters, such as Salmonella or Shigella. These organisms do not metabolize lactose to produce acid, so there is no interaction with the dyes in the medium, resulting in colonies that retain their natural, uncolored appearance.

D. Hemolysis: Hemolysis refers to the breakdown of red blood cells, a phenomenon observed on blood agar, not EMB agar. The colorless colonies on EMB specifically reflect lactose fermentation capability, not hemolytic activity.