<s>[INST] context: TETRACYCLINES These are a class of antibiotics having a nucleus of four cyclic rings. Mechanism of action The tetracyclines a :- c primarily bacteriostatic; inhibit protein synthe:"i&; by binding to 305 ribosomes in susceptible organism. Subsequent to such binding, attachmer. : o f aminoacyl-t-RNA to the mRNA-ribosomc complex is interferred with. A ntimicrobial spectrum When originally introduced, tetracyclines inhibited practically all tvpes of pathogenic microorganisms except fungi and viruses; hence the name &;broad-spectrum antibiotic&;. However, promiscous and often indiscriminate use has gradually narrowed the field of their usefulness. 1. Cocci: All gram-positive and gram-negative cocci were originally sensitive, but now many Strep. pyogenes, Staph. aureus and enterococci have become resistant. Responsiveness of Strep. pneumoniae has decreased somewhat. Tetracyclines (especially minocycline) are now active against few N. gonorrhoeae and N. meningitidis. 2. Most gram-positive bacilli, e.g. Clostridia and other anaerobes, Listeria, Corynebacteria, Propionibacterium acnes, B. anthracis are inhibited but not Mycobacteria, except some atypical ones. 3. Sensitive gram-negative bacilli are-H. ducreyi, Calymmatobacterium granulomatis, V. cholerae, Yersinia pestis, Y. enterocolitica, Campylobacter, Helicobacter pylori, Brucella, Pasteurella multocida, F. tularensis and many anaerobes; some H. influenzae have become insensitive. Enterobacteriaceae are now largely resistant. Notable bacilli that are not inhibited are Pseudomonas aeruginosa, Proteus, Klebsiella, Salmonella typhi and many Bact. fragilis. MIC against anaerobes is relatively higher. 4. Spirochetes, including T. pallidum and Borrelia are quite sensitive. 5. All rickettsiae (typhus, etc.) and chlamydiae are highly sensitive. 6. Mycoplasma and Actinomyces are moderately sensitive. 7. Entamoeba histolytica and Plasmodia are inhibited at high concentrations. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:710,711,712 [/INST] question: Drug effective against pseudomonas is: | options: A: Penicillin G B: Gentamicin C: Tetracycline D: Chloramphenicol | answer: C </s>