Questions & explanations
1. Compare the spectrum of activity of a natural penicillin (like penicillin G) with a semisynthetic penicillin (like ampicillin).
Penicillin G is a natural penicillin that works well against many Gram-positive bacteria (like streptococci). But it does not work against many Gram-negative bacteria (like E. coli). Ampicillin is a semisynthetic penicillin with a broader spectrum. It can kill both Gram-positive and some Gram-negative bacteria. This is because the chemical change allows ampicillin to get through the outer membrane of Gram-negative bacteria. So ampicillin can treat more types of infections, like urinary tract infections caused by E. coli. However, ampicillin is still not effective against bacteria that make penicillinase. Semisynthetic modifications have expanded the range of bacteria we can treat.
2. What is empiric therapy for febrile neutropenia?
Empiric therapy means starting antibiotics right away, before knowing the exact germ causing the fever. Febrile neutropenia is when a patient has a fever and very low white blood cells (neutrophils), which makes them prone to serious infections. Doctors use broad-spectrum antibiotics that cover many common bacteria, like Pseudomonas. The choice depends on how sick the patient is and their risk factors. Low-risk patients may get oral antibiotics, while high-risk patients need intravenous antibiotics in the hospital. Common regimens include cefepime, piperacillin-tazobactam, or carbapenems. The goal is to quickly treat infection and prevent complications.
3. What is a synthetic antibacterial?
A synthetic antibacterial is a drug that kills bacteria and is made entirely in a laboratory. It is not based on a natural product from a living thing. The first synthetic antibacterial was Prontosil, a red dye that turns into sulfanilamide in the body. Sulfonamides (sulfa drugs) are synthetic and stop bacteria from making folic acid, which they need to grow. Quinolones (like ciprofloxacin) are also synthetic; they stop bacteria from copying their DNA. Oxazolidinones (like linezolid) are newer synthetic drugs that stop bacteria from making proteins. These drugs are important because they can treat infections that resist natural antibiotics.
4. Why was methicillin developed from penicillin?
Methicillin was developed because many bacteria became resistant to penicillin. Penicillin works by breaking the cell wall of bacteria. But some bacteria make an enzyme called penicillinase that destroys penicillin. Scientists changed the chemical structure of penicillin to make methicillin. Methicillin is not destroyed by penicillinase, so it can kill resistant bacteria. This was a big advance in fighting infections. However, later bacteria became resistant to methicillin too, leading to MRSA (methicillin-resistant Staphylococcus aureus). Semisynthetic drugs like methicillin show how we can modify natural products to overcome resistance.
5. What are antimicrobial peptides (AMPs) and how do they kill bacteria?
Antimicrobial peptides (AMPs) are short proteins naturally made by many organisms, including humans, as part of the immune system. They have a positive charge that attracts them to the negatively charged bacterial membranes. Once bound, they insert into the membrane and form pores, causing the bacteria to leak and die. Some AMPs also target internal components like DNA or inhibit cell wall synthesis. AMPs are broad-spectrum and less likely to cause resistance because they attack the membrane. However, they can be toxic to human cells and are expensive to produce. Researchers are modifying AMPs to make them safer and more stable.
6. Why is there a need for new antibiotics despite having many existing ones?
Many existing antibiotics are becoming ineffective because bacteria are evolving resistance. For example, carbapenem-resistant Enterobacteriaceae (CRE) are resistant to most available drugs. The World Health Organization has listed priority pathogens that urgently need new treatments. Without new antibiotics, common infections like pneumonia or urinary tract infections could become untreatable. Also, some antibiotics have serious side effects, so safer alternatives are needed. New antibiotics are also needed to treat infections caused by multidrug-resistant bacteria in hospitals and in patients with weakened immune systems.
7. Give an example of a situation where a doctor would choose combination therapy over monotherapy.
A doctor would choose combination therapy for a serious infection like tuberculosis. Tuberculosis bacteria are very hard to kill and quickly become resistant to a single drug. Using two or more drugs together prevents resistance. Another example is treating infections in a hospital where bacteria are often resistant to many drugs. For instance, a patient with a severe bloodstream infection might get two different antibiotics to cover all possible bacteria. Combination therapy is also used for infections caused by bacteria that are already resistant to one drug. The goal is to make sure the infection is cured completely.
8. How does the efficiency of a Rankine cycle depend on temperature?
The efficiency of a Rankine cycle increases with higher boiler temperature and lower condenser temperature. Higher boiler temperature means more energy is available to do work. Lower condenser temperature allows more heat to be rejected at a lower temperature, increasing the temperature difference. However, material limits restrict maximum boiler temperature. Also, the condenser temperature is limited by the cooling medium (air or water). The efficiency is given by 1 - (condenser temperature)/(boiler temperature) in absolute units. So raising boiler temperature or lowering condenser temperature improves efficiency.
9. What is the mechanism of action of quinolone antibiotics?
Quinolone antibiotics, like ciprofloxacin, work by stopping bacteria from copying their DNA. They target two enzymes: DNA gyrase and topoisomerase IV. These enzymes help unwind and separate DNA strands during replication. When quinolones block them, the bacterial DNA gets tangled and cannot be copied. The bacteria cannot divide and eventually die. Quinolones are broad-spectrum, meaning they kill many types of bacteria. They are used for urinary tract infections, respiratory infections, and some skin infections. Because they attack DNA processes, they are very effective but can have side effects like tendon damage.
10. Give an example of an empiric antibiotic regimen for high-risk febrile neutropenia and explain why it is chosen.
Cefepime is a common empiric regimen for high-risk febrile neutropenia. Cefepime is a fourth-generation cephalosporin that covers many gram-negative bacteria, including Pseudomonas aeruginosa, and some gram-positive bacteria. It is chosen because it has good activity against the most dangerous germs in neutropenic patients. Another option is piperacillin-tazobactam, which adds coverage for anaerobes. Carbapenems like meropenem are used if the patient is very ill or has a history of resistant infections. These regimens are started immediately after blood cultures are taken, and later adjusted based on test results.
11. What are the main challenges in developing new antibiotics?
Developing new antibiotics is difficult because bacteria quickly become resistant to new drugs. The discovery of new antibiotic classes has slowed since the 1980s. Many large pharmaceutical companies have left the field because antibiotics are not very profitable; they are used for short courses and new ones are reserved to prevent resistance. Regulatory hurdles and high costs also discourage development. Additionally, screening natural products often finds known compounds, and designing new synthetic molecules is complex. There is a need for new approaches and economic incentives to encourage antibiotic research.
12. How does combination therapy help prevent antibiotic resistance?
Combination therapy helps prevent resistance because bacteria are less likely to survive two different attacks at once. If a bacterium has a mutation that makes it resistant to one drug, the second drug will still kill it. This means very few bacteria survive to pass on resistance genes. Using two drugs with different ways of killing bacteria is especially effective. For example, one drug may damage the cell wall while another stops protein making. This makes it almost impossible for bacteria to become resistant to both at the same time. Combination therapy is a key strategy to keep antibiotics working longer.