Question

How does the antibiotic streptomycin work?

Short answer

Streptomycin is an antibiotic drug belonging to the class of aminoglycosides, used to treat various bacterial infections. It specifically targets bacterial cells by binding to the bacterial ribosome, a structure responsible for protein synthesis. The main action of streptomycin is inhibiting protein synthesis in bacterial cells by binding to the 30S ribosomal subunit, interfering with the initiation complex formation, inducing misreading of the genetic code, and leading to the premature release of incomplete protein chains. This results in non-functional proteins, inhibiting bacterial growth and eventually causing cell death. Resistance to streptomycin can occur, and it is often used in combination with other antibiotics to counteract this issue.

Step-by-step solution

Understand Streptomycin

Streptomycin is an antibiotic drug, belonging to a class of antibiotics called aminoglycosides. It is derived from the bacterium Streptomyces griseus and is commonly used to treat a variety of bacterial infections, including tuberculosis, plague, and certain types of bacterial meningitis.

Bacterial Targeting

Streptomycin specifically targets bacterial cells, leaving human cells largely unaffected. This selective targeting is achieved through the drug's ability to bind the bacterial ribosome, a cellular structure responsible for protein synthesis. Bacterial ribosomes have a slightly different structure compared to human ribosomes, which allows streptomycin to bind to bacterial ribosomes with high affinity and low affinity for human ribosomes.

Inhibition of Protein Synthesis

The main action of streptomycin is to inhibit protein synthesis in bacterial cells. It does this by binding to the 30S ribosomal subunit in the bacterial ribosome, leading to several effects: 1. It interferes with the initiation complex formation, an early step in protein synthesis. 2. It induces misreading of the genetic code by causing the ribosome to misinterpret the messenger RNA (mRNA) sequence. 3. It leads to the premature release of incomplete protein chains by disrupting the ribosome's ability to elongate the polypeptide chain. Collectively, these effects lead to the production of non-functional proteins, which ultimately inhibits the bacterial growth and eventually causes cell death.

Bacterial Resistance to Streptomycin

Over time, some bacteria can develop resistance to streptomycin. Resistance mechanisms include the production of enzymes that inactivate the drug or alterations in the 30S ribosomal subunit, which reduces the antibiotic's ability to bind and inhibit protein synthesis. To counter resistance, streptomycin is often used in combination with other antibiotics to ensure effective treatment of bacterial infections.

Key concepts

Aminoglycoside Antibiotics

Aminoglycosides are a class of antibiotics that have a crucial role in combating serious infections caused by certain types of bacteria. They are particularly known for their rapid bactericidal activity. Streptomycin, discovered from the bacterium Streptomyces griseus, is one such antibiotic and was the first one to be used against tuberculosis.

These antibiotics share a common chemical structure that is composed of amino sugars connected by glycosidic bonds to a central aminocyclitol ring. This structure allows such antibiotics to bind to the bacterial ribosome with specificity and disrupt protein synthesis. Aminoglycoside antibiotics are potent, but their use is sometimes limited by concerns over toxicities such as nephrotoxicity and ototoxicity, which affect the kidneys and ears, respectively. Despite these potential side effects, they play a significant role in treatment regimens for serious infections where alternative treatment options are limited.

Bacterial Ribosome Targeting

The power of streptomycin, as with other aminoglycosides, lies in its ability to target the bacterial ribosome. Ribosomes are essential molecular machines in all cells that assemble proteins according to genetic blueprints. However, bacterial ribosomes differ slightly in structure from human ribosomes, a difference streptomycin exploits to minimize human cellular damage while attacking bacteria.

Streptomycin binds to the 30S subunit of the bacterial ribosome, preventing it from correctly interpreting genetic codes from mRNA. This high degree of specificity for bacterial ribosomes is what makes streptomycin and other aminoglycosides so effective as antibiotics: by selectively halting bacterial protein production, they can stop an infection with relatively low risk to the patient's own cells.

Inhibition of Protein Synthesis

When it comes to treating bacterial infections, the inhibition of protein synthesis is a major mode of action for defeating the offending microbes. This process is critical because proteins are essential for many functions within the cell, including structure, function, and regulation of the body's tissues and organs.

Once streptomycin has bound to the bacterial ribosome, several adverse events unfold within the bacterial cell: the antibiotic distorts the ribosome's reading frame leading to incorrect amino acids being incorporated into the growing protein chains, which generates aberrant and nonfunctional proteins. Additionally, streptomycin can cause the premature termination and release of these malformed proteins. Without properly functioning proteins, bacteria are unable to maintain their cell walls, synthesize enzymes, or carry out other vital processes, ultimately leading to their demise.

Bacterial Resistance to Antibiotics

Unfortunately, the miracle of antibiotics is not without its Achilles' heel: bacterial resistance. Bacteria, through the forces of evolution, can adapt to the presence of antibiotics like streptomycin and find ways to survive. Some bacteria develop the ability to produce enzymes that chemically modify or degrade the antibiotic, rendering it ineffective. Others undergo genetic mutations that alter their ribosomal subunits, decreasing the affinity of the antibiotic for its target.

Combating resistance involves a multifaceted approach. Clinicians might prescribe streptomycin in combination with other antibiotics to enhance efficacy and reduce the chance of resistance. In the ongoing battle between antibiotic development and bacterial adaptation, medical research continues to seek innovative solutions, such as novel antibiotics or methods to circumvent resistance mechanisms, thereby ensuring the continued effectiveness of these life-saving drugs.