Ch. 9 - Inhibiting Growth of Pathogens in Vivo Using Antimicrobial Agents Flashcards
Chemotherapy
The use of any chemicals (drug) to treat any disease/condition
Antimicrobial agents
The use of any chemical (drug) to treat an infectious disease either by inhibiting or killing the pathogen
Antibiotics
Substance produced by a microorganism that kills or inhibits the growth of other microorganisms
Semisynthetic antibiotic
Antibiotics chemically modified to kill a wider variety of pathogens or reduce side effects
Alexander Fleming
Discovered penicillin
-noticed that the farther away the bacteria were from the mould (which was creating penicillin), the better they grew
Staphylococcus aureus
Gram ( + )
Found in our microbiota, often found in our nose
=> staph infections
MRSA is most common
MRSA
Resistant to beta-lactams antibiotics.
- methicillin, oxacillin, penicillin, and amoxicillin.
Most MRSA infections are skin infections that often appear as a bump, a boil, or area that is red, tender and swollen, and is sometimes confused with a spider bite.
Bactericidal drugs
Agents that kill microbes
Bacteriostatic drugs
Agents that inhibit/slow the growth of microbes, but never actually kills it
How do antimicrobial agents work? (5)
- Inhibition of cell wall synthesis (Bactericidal)
- Damage to cell membrane (Bactericidal)
- Inhibition of nucleic acid synthesis (Bactericidal)
- Inhibition of protein synthesis (Bactericidal or Bacteriostatic)
- Inhibition of enzyme activity (Bacteriostatic)
Sulfonamide drugs
Competitive inhibitors, Bacteriostatic
Inhibit production of follic acid in bacteria that need p-aminobenzoic (PABA) to synthesis it
Without follic acid, bacteria cant produce certain essential proteins, so they die
Penicillin
Bactericidal,
Acts on mostly gram ( + )
Interferes with the synthesis and cross linking of peptidoglycan
Inhibits cell wall synthesis => destroy bacteria
narrow spectrum antibiotic
Use when we know specifically if we have gram ( - ) or ( + ) bacteria
ex: colistin
Broad spectrum antibiotics
Use when we arent sure if the bacteria is gram pos or neg
ex: ampicillin
Multi drug therapy
2+ drugs used simultaneously
ex: Tx tuberculosis
Synergism (drug related)
2 anitmicrobial agents are used together to produce a degree of pathogen killing greater than what just one of the drugs alone could do
Antagonism (drug related)
The 2 drugs work against each other. The extent of pathogen killing is less than what each drug could have reached alone
Categories of antibacterial agents
- Cephalosporins (bactericial)
- interefere with cell wall synthesis
- Tetracycline (bacteriostatic)
- inhibit protei synthesis
- Aminoglycosides (bactericidal)
- inhibit protein synthesis
- Macrolides (low does bacteriostatic; high dose bactericidal)
- inhibit protein synthesis
- Fluoroquinolones (bactericidal)
- inhibit DNA synthesis
3 ways that anti-fungal agents work
- bind with cell membrane steroids
- interfere with sterol synthesis
- block mitosis or nucleic acid synthesis
Why do antifungal and antiprotozoal tend to be more toxic to humans?
They are also eukaryotic, so it is hard to finda gents that will specifically target the microbes compared to those in our body
2 ways antiprotozoal agents work
- Interfere with RNA/DNA synthesis
2. Interfere with protozoal metabolism
How do antivirals work?
Inhibiting viral replication
Superbug
Microbes (mainly bacteria) that have become resistant to one or more microbial agents
Intrinsic resistance
Naturally resistant ebcause they lack the specific target site for the drug or the drug is unable to cross cell membrane, therefore cannot reach its site of action
Acquired resistance
Bacteria were once susceptible, but they become resistant
Mechanisms of acquired resistance
- chromosomal mutation => change shape of drug binding site
effect: drug cant bind - chromosomal mutation => change in cell membrane permeability
effect: drug cant pass through membrane - Acquisition of a gene that enables bacterium to produce an enzyme that destroys or inactivates the drug
ex: penicillinase acquired during conjugation and chews up penicillin - Acquisition of a gene that enables the bacteria to produce MDR pump
effect: drug is pumped out of the cell before it can damage/kill the cell
B-lactamases
Produced by some bacteria to derstoy the B-lactam ring of penicillin.
no ring= no drug function
3 strategies against drug resistance
- educate health professionally and patients
- patients stop demanding antibiotics and professionals stop prescribing them when not needed
- Not used in a prophylactic way
Empiric therapy
When drug therpay is started before the lab results are available.
- time constraint
- educated guess
- consideration of medical Hx, site of infection, pt age..
4 reasons why antimicrobial agents shouldn’t be used indiscriminately
- selecting for resistant organisms
- Allergies
- Toxicity
- Flora => superinfection
