Revise Antibiotics for Cambridge 9700 (10.2)

Inhibition of Cell Wall Synthesis: This is a common target as eukaryotes lack a peptidoglycan cell wall. Antibiotics like penicillin and vancomycin interfere with the synthesis of peptidoglycan, weakening the cell wall and causing the bacterium to lyse (burst) due to osmotic pressure.

Inhibition of Protein Synthesis: Bacteria have 70S ribosomes, while eukaryotes have 80S ribosomes. Antibiotics like tetracyclines, streptomycin, and erythromycin can specifically bind to bacterial 70S ribosomes and disrupt protein synthesis, halting bacterial growth and replication.

Inhibition of Nucleic Acid Synthesis: Some antibiotics interfere with enzymes essential for DNA replication or transcription in bacteria, such as DNA gyrase. Quinolones (e.g., ciprofloxacin) are an example.

Disruption of Cell Membrane Function: Antibiotics like polymyxins can disrupt the structure of the bacterial cell membrane, increasing its permeability and causing leakage of essential cellular contents. This mechanism is less common as eukaryotic cell membranes are similar, leading to lower selective toxicity.

Inhibition of Metabolic Pathways: Some antibiotics, like sulfonamides, block essential metabolic pathways in bacteria that are absent in humans. For example, they inhibit the synthesis of folic acid, which bacteria must produce themselves, while humans obtain it from their diet.

Genetic Variation: Random mutations in bacterial DNA create genetic diversity. Some mutations may alter the target of an antibiotic or create a new enzyme.

Selective Pressure: The presence of an antibiotic kills susceptible bacteria.

Survival and Reproduction: Bacteria with the resistance mutation survive the antibiotic treatment.

Inheritance: The surviving resistant bacteria reproduce, passing the resistance gene to their offspring (vertical gene transmission). Over time, the frequency of the resistance allele increases, and the population becomes predominantly resistant.

Conjugation: The most common method. Bacteria connect via a pilus and transfer a copy of a plasmid (a small, circular piece of DNA) containing one or more resistance genes.

Transformation: Bacteria take up 'naked' DNA fragments from their environment, which may have been released from dead bacteria. If this DNA contains a resistance gene, it can be incorporated into the recipient's genome.

Transduction: A bacteriophage (a virus that infects bacteria) accidentally packages bacterial DNA (including resistance genes) from one bacterium and transfers it to another during infection.

Enzymatic Degradation: Bacteria produce enzymes that inactivate the antibiotic. A key example is β-lactamase, which breaks the β-lactam ring in penicillin and related antibiotics, rendering them useless.

Altered Target Site: Mutations change the shape of the antibiotic's target (e.g., ribosomes or enzymes), so the antibiotic can no longer bind effectively.

Efflux Pumps: Bacteria develop protein pumps in their cell membrane that actively pump the antibiotic out of the cell before it can reach its target and accumulate to toxic levels.

Reduced Permeability: Changes in the bacterial cell wall or membrane (e.g., altering porin channels) can reduce the entry of antibiotics into the cell.

What is MRSA?: A 'superbug' strain of Staphylococcus aureus that is resistant to methicillin and many other common beta-lactam antibiotics. It is a major cause of hospital-acquired infections.

Increased Morbidity and Mortality: Resistant infections lead to longer illnesses, increased hospital stays, and higher death rates.

Higher Healthcare Costs: Treating resistant infections requires more expensive, often more toxic, 'last-resort' antibiotics and intensive care.

Threat to Modern Medicine: Procedures like surgery, organ transplants, and chemotherapy become much riskier without effective antibiotics to prevent or treat associated bacterial infections.

Prudent Use of Antibiotics: Only use antibiotics when prescribed by a doctor, and always complete the full course to ensure all bacteria are eliminated. Do not use antibiotics for viral infections like the common cold, as they have no effect.

Improved Hygiene and Infection Control: Good hygiene practices, especially in hospitals (e.g., handwashing), can prevent the spread of resistant bacteria like MRSA.

Narrow-Spectrum Antibiotics: Use narrow-spectrum antibiotics that target the specific pathogen whenever possible, rather than broad-spectrum antibiotics that kill a wide range of bacteria and can promote resistance.

Regulation: Reduce the use of antibiotics in agriculture and animal husbandry, where they are often used for growth promotion rather than treating disease.

Research and Development: Invest in the development of new antibiotics, alternative treatments (like phage therapy), and rapid diagnostic tools to identify bacterial infections quickly.