أسئلة ريتين الخامسة ميكرو دمياط (قبل التعديل)

Antimicrobials

• Definitions: Antimicrobials are naturally occurring or synthetically derived compounds that inhibit or destroy bacteria. Ideal antibiotics have selective toxicity, don't encourage bacterial resistance, are non-allergenic, and are well distributed in tissues.

• Classification: Antimicrobials are categorized by the type of microorganism they target (e.g., antiprotozoal, antifungal, antiviral, antihelminthic). Antibiotics are specifically for bacteria.

• Bactericidal vs. Bacteriostatic: Bactericidal antibiotics kill bacteria, while bacteriostatic antibiotics inhibit bacterial growth, eventually leading to cell death.

• Examples of Bactericidal Antibiotics: Aminoglycosides, Beta-lactams, Vancomycin, Quinolones, Rifampin, Metronidazole. (These are examples, not an exhaustive list).

• Examples of Bacteriostatic Antibiotics: Chloramphenicol, Clindamycin, Erythromycin, Sulfonamides, Trimethoprim, Tetracyclines. (These are examples, not an exhaustive list).

Mechanisms of Action of Antibiotics

• Cell Wall Synthesis Inhibitors: These antibiotics target the synthesis of peptidoglycan, a key component of bacterial cell walls. Examples include penicillins, cephalosporins, and vancomycin.

• Penicillins: Natural penicillins are effective against Gram-positive cocci (except Staphylococcus aureus). Penicillinase-Resistant Penicillins (like Methicillin) are used for Staphylococcus infections, while Extended-Spectrum Penicillins (like Amoxicillin) treat various Gram-negative bacteria. Some penicillins are effective against Pseudomonas aeruginosa. Bacteria produce enzymes called beta-lactamases that break down penicillins, but clavulanate and other agents prevent this.

• Cephalosporins: These antibiotics are similar to penicillins but have broader activity spectra. Different generations demonstrate different activity and resistance to beta-lactamases.

• Protein Synthesis Inhibitors: Some antibiotics target bacterial ribosomes, which are essential for protein synthesis. Examples include aminoglycosides, tetracyclines, macrolides, chloramphenicol, and streptogramins. Different antibiotics interact with different ribosomal parts.

Other Mechanisms

• Inhibitors of Nucleic Acid Synthesis: Some antibiotics inhibit bacterial DNA or RNA synthesis. Examples include quinolones (e.g., ciprofloxacin) and rifampicin. They target bacterial DNA gyrase or other enzymes.

• Alteration of Cell Membrane Function: Other antibiotics disrupt the integrity of the bacterial cell membrane (e.g., polymyxins, daptomycin).

• Inhibitors of Folate Synthesis: Certain antibiotics like cotrimoxazole interfere with bacterial folate synthesis, a crucial metabolic pathway.

Antimicrobial Combination

• Indications: Combination therapy can enhance antimicrobial activity, reduce toxicity, and prevent the development of antibiotic resistance.

• Disadvantages: Combination therapy can be more costly and can result in adverse patient reactions.

Probiotics

• Definition: Live, non-pathogenic bacteria or yeasts that offer health benefits.

• Mechanism: They prevent pathogens from adhering to the gut lining, improve immunity, and influence the gut microbiome.

• Advantages: Probiotics reduce diarrhea, improve immunity (especially in young children), potentially reduce antibiotic-associated diarrhea, and help patients with weakened or damaged immune systems.

• Complications: Some probiotic strains might cause complications in severely immunocompromised patients or those with indwelling catheters.

Bacterial Resistance to Antibiotics

• Failure of Antibiotic Treatment: Causes of treatment failure include viral co-infection, inaccurate/insufficient dosage, inappropriate treatment duration, etc.

• Antibiotic Misuse: Overuse, inadequate dosage, and misuse lead to the emergence of resistant strains.

• Antibiotic Resistance Mechanisms: These mechanisms include reduced antibiotic uptake, inactivation of the antibiotic, and mutation in the target site.

•  Reduced permeability (e.g., efflux pumps)

•  Inactivation by enzymes (e.g., β-lactamases)

•  Alteration of the target sites of the antibiotic

•  Metabolic bypass pathways

Clinical Case

• A 45-year-old female presented with fever, burning urination, frequency, and dysuria. Microbiology identified Gram-negative bacilli, and Nitrofurantoin was prescribed.