Antibiotics Flashcards
Mechanisms of action
- inhibition of bacterial cell wall
- inhibition of nucleic acid synthesis
- inhibition of protein synthesis
- inhibition of cell membrane
- inhibition of folic acid synthesis
Inhibition of Cell Wall Synthesis
- Bacteriostatic
- Penicillin and Cephalosporins- block cross-linking between peptidoglycans
- Vancomycin- Blocks peptidoglycan elongation
- Cycloserine- Prevents the cell from making NAG and NAM
Penicillin
- Penicillium Chrysogenum
- A diverse group: 1st, 2nd, and 3rd generations
- Natural: Penicillin G and V
- Semisynthetic: Ampicillin and Carbenicillin
- Structure: - Thiazolidine ring - Beta-Lactam Ring- Variable side chain (R group)
Cephalosporin
- Cephalosporin Acremonium (mold)
- Widely Administered today
- Diverse Group: (natural and semisynthetic): 1st, 2nd, 3rd, and 4th generations
- Structure: similar to Penicillin except it has a different main group and it has 2 sites for R groups
The structure of cephalosporin:
The different R groups allow for versatility and improved effectiveness
Inhibition of Protein Synthesis
Chloramphenicol-
Aminoglycosides-
Tetracycline-
Erythromycin-
Chloramphenicol:
- binds to 50s ribosomal subunits
- prevents peptide bond formation
- inhibits protein synthesis
- broad-spectrum
- treats typhoid fever and brain abscesses
- rarely used now due to side effects: aplastic anemia
Aminoglycosides:
- binds to 30s ribosomal subunits
- causes misreading of mRNA
- inhibits protein synthesis
- from Streptomyces ssp.
- Streptomyces synthesizes many different types of antibiotics, such as; erythromycin, chloramphenicol, and tetracycline.
Tetracycline:
- blocks attachment of tRNA
- inhibits protein synthesis
- broad-spectrum and low cost
- commonly used to treat STD’s
- minor side effects: gastrointestinal disruption
Erythromycin:
- inhibits protein synthesis
- broad-spectrum
- commonly used as prophylactic drug prior to surgery
- side effects: low toxicity
Injury to the plasma membrane:
- polymyxin B (gram negative)
- topical (triple antibiotic ointment)
- combined with bacitracin and neomycin (broad spectrum) in OTC preparation
- neosporin
Inhibitors of Nucleic Acid Synthesis
Rifamycin:
- inhibits RNA synthesis
- Antituberculosis
Quinolones and fluoroquinolones:
- UTI’s
- inhibits DNA gyrase (enzyme that helps wind up DNA once it’s been replicated)
- Ciprofloxacin
Folic Acid Synthesis
Sulfonamides (sulfa drug) and trimethoprim
- competitive inhibition of enzymes
- analogs
- prevents the metabolism of DNA, RNA, and amino acids
- -this works because mammals get folic acid from their diet and bacteria mush make their own
Antivirals
- increasing types of drugs becoming available, however; it is difficult to maintain selective toxicity
- effective drugs- target replication cycle: entry, nucleic acid synthesis, and assembly/release.
- INTERFERON= genetically engineered antiviral protein from a human gene
Antiviral medications and what they treat:
- blocking viral entry: tamiflu- blocks the action of neuraminidases of influenza virus
- blocking viral replication: Zidovudine (AZT)- blocks reverse transcription of HIV
- inhibiting viral cleavage: Protease inhibitors- block HIV protease
Other types of antimicrobials:
Antifungal- ketoconizole treats valley fever
Antiprotozoal- metronidazole treats giardia
Antimalarial- quinine treats malaria
Anthelmintic- mebendazole treats tapeworms and roundworms
Mechanisms of Antibiotic Resistance
- Rapid ejection of the drug
- Alteration of drug’s target site
- Prevention of penetration of drug
- Enzymatic destruction of drug
Antimicrobial Resistance means:
a relative or complete lack of effect of antimicrobial against a previously susceptible microbe
Antibiotic Resistance means:
Intermicrobial transfer of plasmids containing resistance genes (R factors) occurs by conjugation, transformation, and transduction
What factors promote antimicrobial resistance?
- Exposure to sub-optimal levels of antimicrobial
- inappropriate use
- exposure to microbes carrying resistance genes
Inappropriate Antimicrobial Use:
- prescriptions not being taken correctly
- antibiotics for viral infections
- antibiotics sold OTC without medical supervision
- spread of resistant microbes (C. difficile) in hosptials
- inadequate surveillance or defective susceptibility assays (giving drugs that are not effective)
- poverty or war (penicillin)
- use of antibiotics in food
Antibiotics in Food
Antibiotics are used in animal feeds and sprayed on plants to prevent infection and to promote growth.
- tetracycline in the soil
Multi drug-resistant Salmonella Typhi has been found in 4 states in 18 people who ate beef fed antibiotics
Antibiotic Drug and Host Interaction
- Toxicity to organs
- Allergic reactions
- suppress/ alter microflora
- effective drugs
What can tetracycline treatments do to the teeth?
it can cause teeth discoloration
Disrupting the normal flora in the intestines can result in:
superinfections
Finding an effective drug for treatments:
- Identifying infectious agent (culture)
- Perform sensitivity testing (on Mueller Hinton Agar)
- Often the Minimum Inhibitory Concentration (MIC) is determinined
Consequences of Antimicrobial Resistance
infections resistant to available antibiotics and increases cost of treatment
