Antibiotic Production Practice Questions

Correct answer: Secondary metabolites

Antibiotics are secondary metabolites because they are produced during the stationary phase (idiophase) of microbial growth. Unlike primary metabolites, they are not essential for the growth, development, or reproduction of the organism.

Correct answer: Streptomyces species

Streptomyces, a genus of Actinobacteria, is responsible for producing over two-thirds of the world's clinically useful antibiotics, including streptomycin and tetracycline. Their complex secondary metabolism is highly specialized for producing bioactive compounds.

Correct answer: Idiophase

The idiophase is the period following the rapid growth phase where the concentration of secondary metabolites, such as antibiotics, increases. This phase occurs when essential nutrients are depleted or growth rates slow down.

Correct answer: To provide the side chain for the antibiotic molecule

In the production of Penicillin G, phenylacetic acid is added as a precursor to provide the specific benzyl side chain. Without the addition of specific precursors, the mold Penicillium chrysogenum would produce a mixture of different penicillins.

Correct answer: Solvent extraction

Downstream processing of antibiotics typically involves solvent extraction, where the antibiotic is moved from the aqueous fermentation broth into an organic solvent. This is followed by further purification steps like chromatography and crystallization.

Correct answer: Corn steep liquor

Corn steep liquor, a byproduct of the corn milling industry, was found to dramatically increase penicillin yields. It provided a rich source of nitrogen, vitamins, and minerals that favored the production of secondary metabolites.

Correct answer: Amoxicillin

Amoxicillin is a semi-synthetic antibiotic derived by chemically modifying the 6-aminopenicillanic acid (6-APA) nucleus obtained from natural fermentation. Semi-synthetic drugs are designed to be more stable or have a broader spectrum of activity than their natural counterparts.

Correct answer: Stirred-tank bioreactor

The stirred-tank bioreactor is preferred for antibiotic production because it provides efficient oxygen transfer, pH control, and uniform nutrient distribution. Most antibiotic-producing microbes, like Streptomyces and Penicillium, are obligate aerobes.

Correct answer: The product inhibits its own biosynthesis

Feedback inhibition is a regulatory mechanism where the final product (the antibiotic) inhibits the activity of enzymes earlier in the biosynthetic pathway. Industrial microbiologists use mutant strains that are less sensitive to this inhibition to achieve higher yields.

Correct answer: Streptomyces griseus

Streptomyces griseus is the specific species used industrially to produce Streptomycin. It was the first antibiotic found to be effective against tuberculosis.

Correct answer: Glucose

High concentrations of glucose can repress the genes responsible for secondary metabolism, a phenomenon known as glucose catabolite repression. To avoid this, industrial processes often use 'fed-batch' systems or slower-metabolizing sugars like lactose.

Correct answer: Cephalosporin

Cephalosporins are produced by the fungus Cephalosporium (now Acremonium). Most other common antibiotics like tetracyclines and macrolides are produced by various species of the bacterial genus Streptomyces.

Correct answer: Feeding an analog of a precursor to a mutant strain to create a new antibiotic

In mutational biosynthesis, a mutant strain that cannot produce a natural precursor is fed an altered version of that precursor. This results in the production of a novel 'hybrid' antibiotic that may have better clinical properties.

Correct answer: Testing thousands of microbial extracts for antimicrobial activity

High-throughput screening uses automated robotics and microtiter plates to rapidly test large libraries of chemical compounds or microbial extracts for their ability to inhibit the growth of pathogens. This accelerates the drug discovery process.

Correct answer: Microbial growth and antibiotic stability are highly pH-dependent

Changes in pH can alter enzyme activity and the solubility of nutrients. Furthermore, many antibiotics are chemically unstable and can be degraded if the fermentation broth becomes too acidic or too alkaline.

Correct answer: Using genetic engineering or selection to increase the yield of a product

Strain improvement involves using techniques like mutagenesis (UV/chemicals) or recombinant DNA technology to create 'overproducing' strains. This significantly reduces the cost of production by increasing the amount of antibiotic produced per liter of broth.

Correct answer: Amphotericin B

Amphotericin B is a polyene antifungal produced by Streptomyces nodosus. While Streptomyces is famous for antibacterials, it also produces many other types of bioactive compounds, including antifungals and immunosuppressants.

Correct answer: It produces the antibiotic in a highly pure, solid form

Crystallization is one of the final steps in downstream processing. By adjusting temperature or solvent concentration, the antibiotic is forced to form pure crystals, which are then harvested, dried, and packaged for medical use.

Correct answer: The step-wise scaling up of microbial volume from a vial to the main fermenter

Inoculum development involves growing the culture in increasingly larger volumes (from shake flasks to seed tanks) to ensure a healthy, active population of microbes is ready to begin the main production phase in the large fermenter.