One important heterolactic fermenter is Leuconostoc mesenteroides , which is used for souring vegetables like cucumbers and cabbage, producing pickles and sauerkraut, respectively. Lactic acid bacteria are also important medically. The production of low pH environments within the body inhibits the establishment and growth of pathogens in these areas.
For example, the vaginal microbiota is composed largely of lactic acid bacteria, but when these bacteria are reduced, yeast can proliferate, causing a yeast infection. Additionally, lactic acid bacteria are important in maintaining the health of the gastrointestinal tract and, as such, are the primary component of probiotics. Another familiar fermentation process is alcohol fermentation , which produces ethanol.
The ethanol fermentation reaction is shown in Figure 1. In the first reaction, the enzyme pyruvate decarboxylase removes a carboxyl group from pyruvate, releasing CO 2 gas while producing the two-carbon molecule acetaldehyde. The ethanol fermentation of pyruvate by the yeast Saccharomyces cerevisiae is used in the production of alcoholic beverages and also makes bread products rise due to CO 2 production.
Outside of the food industry, ethanol fermentation of plant products is important in biofuel production. Figure 1. The chemical reactions of alcohol fermentation are shown here. Ethanol fermentation is important in the production of alcoholic beverages and bread.
Without these pathways, glycolysis would not occur and no ATP would be harvested from the breakdown of glucose. Many of these different types of fermentation pathways are also used in food production and each results in the production of different organic acids, contributing to the unique flavor of a particular fermented food product.
The propionic acid produced during propionic acid fermentation contributes to the distinctive flavor of Swiss cheese, for example. Several fermentation products are important commercially outside of the food industry.
For example, chemical solvents such as acetone and butanol are produced during acetone-butanol-ethanol fermentation. Complex organic pharmaceutical compounds used in antibiotics e.
Fermentation products are used in the laboratory to differentiate various bacteria for diagnostic purposes. For example, enteric bacteria are known for their ability to perform mixed acid fermentation, reducing the pH, which can be detected using a pH indicator. Similarly, the bacterial production of acetoin during butanediol fermentation can also be detected.
Gas production from fermentation can also be seen in an inverted Durham tube that traps produced gas in a broth culture. Microbes can also be differentiated according to the substrates they can ferment. For example, E. The ability to ferment the sugar alcohol sorbitol is used to identify the pathogenic enterohemorrhagic OH7 strain of E.
Last, mannitol fermentation differentiates the mannitol-fermenting Staphylococcus aureus from other non—mannitol-fermenting staphylococci. Identification of a microbial isolate is essential for the proper diagnosis and appropriate treatment of patients. Scientists have developed techniques that identify bacteria according to their biochemical characteristics.
Typically, they either examine the use of specific carbon sources as substrates for fermentation or other metabolic reactions, or they identify fermentation products or specific enzymes present in reactions. In the past, microbiologists have used individual test tubes and plates to conduct biochemical testing.
However, scientists, especially those in clinical laboratories, now more frequently use plastic, disposable, multitest panels that contain a number of miniature reaction tubes, each typically including a specific substrate and pH indicator. After inoculation of the test panel with a small sample of the microbe in question and incubation, scientists can compare the results to a database that includes the expected results for specific biochemical reactions for known microbes, thus enabling rapid identification of a sample microbe.
These test panels have allowed scientists to reduce costs while improving efficiency and reproducibility by performing a larger number of tests simultaneously. Many commercial, miniaturized biochemical test panels cover a number of clinically important groups of bacteria and yeasts. Currently, the various API strips can be used to quickly and easily identify more than species of bacteria, both aerobic and anaerobic, and approximately different types of yeasts.
Based on the colors of the reactions when metabolic end products are present, due to the presence of pH indicators, a metabolic profile is created from the results Figure 2.
Figure 2. The API 20NE test strip is used to identify specific strains of gram-negative bacteria outside the Enterobacteriaceae. However, his sluggish reflexes along with his light sensitivity and stiff neck suggest some possible involvement of the central nervous system, perhaps indicating meningitis. Meningitis is an infection of the cerebrospinal fluid CSF around the brain and spinal cord that causes inflammation of the meninges, the protective layers covering the brain.
Meningitis can be caused by viruses, bacteria, or fungi. Although all forms of meningitis are serious, bacterial meningitis is particularly serious. After a 3-hour drive to the hospital, Alex was immediately admitted. Physicians took a blood sample and performed a lumbar puncture to test his CSF. They also immediately started him on a course of the antibiotic ceftriaxone, the drug of choice for treatment of meningitis caused by N. Skip to main content. Microbial Metabolism.
Such fermentation patterns can be used to identify and classify bacteria. During the s, the French microbiologist Louis Pasteur studied fermenting bacteria. He demonstrated that fermenting bacteria could contaminate wine and beer during manufacturing, turning the alcohol produced by yeast into acetic acid vinegar. Pasteur also showed that heating the beer and wine to kill the bacteria preserved the flavor of these beverages. The process of heating, now called pasteurization in his honor, is still used to kill bacteria in some alcoholic beverages, as well as milk.
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