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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.g., penicillin), vaccines, and vitamins are produced through mixed acid fermentation . 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. coli can ferment lactose, forming gas, whereas some of its close gram-negative relatives cannot. The ability to ferment the sugar alcohol sorbitol is used to identify the pathogenic enterohemorrhagic O157:H7 strain of E. coli because, unlike other E. coli strains, it is unable to ferment sorbitol. Last, mannitol fermentation differentiates the mannitol-fermenting Staphylococcus aureus from other non–mannitol-fermenting staphylococci.
| Common Fermentation Pathways | |||
|---|---|---|---|
| Pathway | End Products | Example Microbes | Commercial Products |
| Acetone-butanol-ethanol | Acetone, butanol, ethanol, CO 2 | Clostridium acetobutylicum | Commercial solvents, gasoline alternative |
| Alcohol | Ethanol, CO 2 | Candida, Saccharomyces | Beer, bread |
| Butanediol | Formic and lactic acid; ethanol; acetoin; 2,3 butanediol; CO 2 ; hydrogen gas | Klebsiella, Enterobacter | Chardonnay wine |
| Butyric acid | Butyric acid, CO 2 , hydrogen gas | Clostridium butyricum | Butter |
| Lactic acid | Lactic acid | Streptococcus, Lactobacillus | Sauerkraut, yogurt, cheese |
| Mixed acid | Acetic, formic, lactic, and succinic acids; ethanol, CO 2 , hydrogen gas | Escherichia, Shigella | Vinegar, cosmetics, pharmaceuticals |
| Propionic acid | Acetic acid, propionic acid, CO 2 | Propionibacterium, Bifidobacterium | Swiss cheese |
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. One of the earliest and most popular test panels is the Analytical Profile Index (API) panel invented in the 1970s. Once some basic laboratory characterization of a given strain has been performed, such as determining the strain’s Gram morphology, an appropriate test strip that contains 10 to 20 different biochemical tests for differentiating strains within that microbial group can be used. Currently, the various API strips can be used to quickly and easily identify more than 600 species of bacteria, both aerobic and anaerobic, and approximately 100 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 ( [link] ). Microbiologists can then compare the sample’s profile to the database to identify the specific microbe.
Many of Hannah’s symptoms are consistent with several different infections, including influenza and pneumonia. However, her sluggish reflexes along with her 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. Bacterial meningitis may be caused by several different bacteria, but the bacterium Neisseria meningitidis , a gram-negative, bean-shaped diplococcus, is a common cause and leads to death within 1 to 2 days in 5% to 10% of patients.
Given the potential seriousness of Hannah’s conditions, her physician advised her parents to take her to the hospital in the Gambian capital of Banjul and there have her tested and treated for possible meningitis. After a 3-hour drive to the hospital, Hannah was immediately admitted. Physicians took a blood sample and performed a lumbar puncture to test her CSF. They also immediately started her on a course of the antibiotic ceftriaxone, the drug of choice for treatment of meningitis caused by N. meningitidis , without waiting for laboratory test results.
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The microbe responsible for ethanol fermentation for the purpose of producing alcoholic beverages is ________.
yeast ( Saccharomyces cerevisiae )
________ results in the production of a mixture of fermentation products, including lactic acid, ethanol and/or acetic acid, and CO 2 .
Heterolactic fermentation
Fermenting organisms make ATP through the process of ________.
glycolysis
Match the fermentation pathway with the correct commercial product it is used to produce:
| ___acetone-butanol-ethanol fermentation | a. bread |
| ___alcohol fermentation | b. pharmaceuticals |
| ___lactic acid fermentation | c. Swiss cheese |
| ___mixed acid fermentation | d. yogurt |
| ___propionic acid fermentation | e. industrial solvents |
e; 2. a; 3. d; 4. b; 5. c
Why are some microbes, including Streptococcus spp., unable to perform aerobic respiration, even in the presence of oxygen?
How can fermentation be used to differentiate various types of microbes?
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