Answer:

In the multiple tube fermentation technique, the formation of acid and gas is an important indicator for the presence of certain microorganisms, particularly in the field of microbiology and biochemical engineering. The acid and gas formation occurs as a result of the metabolic activities of microorganisms, such as bacteria or yeast, during the fermentation process.

Explanation:

Multiple tube fermentation technique:
The multiple tube fermentation technique is a commonly used method for detecting the presence and determining the characteristics of microorganisms in a sample. It involves inoculating the sample into multiple tubes containing specific growth media and observing the growth and metabolic activity of the microorganisms.

Formation of acid and gas:
During fermentation, microorganisms metabolize the available nutrients in the growth medium, which can result in the production of various metabolic byproducts. One of the commonly observed byproducts is the formation of acid, which can be detected by changes in the pH of the medium. Additionally, some microorganisms also produce gas as a byproduct of their metabolic activity.

Positive test:
If acid and gas are formed in the multiple tube fermentation technique, it indicates a positive test. This means that the microorganisms present in the sample are capable of fermenting the specific nutrients in the growth medium and producing acid and gas as metabolic byproducts. The formation of acid and gas is typically indicated by changes in the color of the growth medium, the presence of gas bubbles, or the production of gas in a Durham tube.

Continued test:
A positive test result indicates that the microorganisms of interest are present in the sample and are actively fermenting the nutrients in the growth medium. In this case, the test is continued by further analyzing the characteristics of the microorganisms, such as their identification, quantification, or their specific metabolic pathways.

Negative test:
If no acid or gas is formed in the multiple tube fermentation technique, it indicates a negative test. This means that the microorganisms of interest are either not present in the sample or are unable to metabolize the specific nutrients in the growth medium to produce acid and gas. A negative test result suggests that alternative methods may be required to detect and identify the microorganisms in the sample.

Discarded test:
If the test is discarded, it means that the results obtained from the multiple tube fermentation technique are inconclusive or unreliable. This could occur due to contamination of the growth medium, improper handling of the samples, or other experimental errors. In such cases, it is necessary to repeat the test or use alternative methods to obtain accurate and reliable results.