Anti microbial therapy Flashcards
Antimicrobial agent
a special group of chemotherapeutic agents used to treat diseases caused by microbes
chemotherapeutic agent
any chemical substance used in medical practice (drugs)
Spectrum of activity
the range of different microbes against which an antimicrobial agent acts
Broad spectrum
agents that are effective against a great number of microorganisms from a wide range of taxonomic groups, including both gram-positive and gram–negative bacteria
Narrow spectrum
agents that are effective against only a small number of microorganisms or a single taxonomic group
5 major modes of action that antibiotics have on bacterial cells
- inhibition of cell wall synthesis
- disruption of cell membrane function
- inhibition of protein sythesis
- inhibition of nucleic acid synthesis
- action as antimetabolites
Antibiotics that inhibit cell wall synthesis
penicillin (natural), penicillin (semisynthetic), cephalosporins, carbapenems, bacitracin
Natural penicillin
treats a wide variety of infections, mostly gram positive bacteria
has relatively few side affects but allergies
Semisynthetic Penicillin
treats infections that are resistant to natural penicillin
few side effects as well
Cephalosporins
treats a wide variety of infections when allergy or toxicity makes other agents unsuitable
relatively non toxic, but can lead to superinfections
carbapenems
mixed infections, nosocomial infections, infections of unknown etiology
allergic reations, superinfections, seizures, gastrointestinal disturbances
Bacitracin
treats skin infections
internal use is toxic to the kidneys
Antibiotics that disrupt cell membrane function
polymyxins and tyrocidins
Polymyxins
treats skin infections
internal use can be highly toxic
Tyrocidins
treats skin infections cause by gram positive cocci
internal use can be highly toxic
Antibiotics that inhibit protein synthesis
streptomycin, gentamicin and other aminoglycosides, tetracyclines, chloramphenicol, erthromycin
Streptomycin
treats tuberculosis
can damage kidneys and the inner ear
Gentamicin and other aminoglycosides
treats antibiotic resistant and hospital acquired infections
can cause varying degrees of kidney and inner ear damage
chloramphenicol
treats a broad spectrum of bacterial infections, brain abscesses, and penicillin resistant infections
can damage bone marrow and cause aplastic anemia
tetracyclines
treats a broad spectrum of bacterial infections and some fungal infections
can stain teeth, cause gastrointestinal symptoms, and can lead to super infections
Erythromycin
treats gram positive bacterial infections, some penicillin resistant infections, and legionnaires’ disease
Antibiotics that inhibit nucleic acid synthesis
rifampin and quinolones
Rifampin
treats tuberculosis and to eliminate meningocci from the naspharynx
can cause bright orange or red urine, saliva, tears, and skin; liver damage; and many disorders when used with other agents
Quinolones
Treats UTI’s, traveller’s diarreah, and effective against many drug resistant organisms
can cause nausea, headaches and other nervous system disturbances
Antibiotics that act as anitmetabolites
sulfonamides, isoniazid, ethambutol, and nitrofurantoin
Sulfonamides
treats some kinds of meningitis and suppresses intestinal flora before colon surgery
earlier forms caused kidney damage, however current ones do not
Isoniazids
treats tuberculosis
can cause pyridoxine deficiency
Ethambutol
Treats tuberculosis
may cause pyridoxine deficiency
Nitrofurantonin
treats UTI’s
can cause nausea and vomiting
Common side effects of antimicrobial agents on include
toxicity, allergy, and disruption of normal microflora
superinfection
invasion by replacement microflora
5 mechanisms of resistance in bacteria
- Alteration of targets
- Alteration of membrane permeability
- development of enzymes
- alteration of an enzyme
- alteration of a metabolic pathway
- Alteration of targets
mutation alters DNA such that the protein produced or targeted is modified. Antimicrobial agents can no longer bind to the target
- Alteration of Membrane Permability
this occurs when new genetic info changes the nature of proteins in the membrane. such alterations change membrane transport systems or pores in the membrane so that an antimicrobial agent can no longer cross the membrane
- Development of Enzymes
this common cause of resistance can destroy or inactivate antimicrobial agents. The most common enzyme of this type is called B-lactamase
B-lactamase
exist in various bacteria, and they are capable of breaking the B-lactam ring in penicillins and some cephalosporins
- Alteration of an enzyme
allows a formerly inhibited reaction to occur
- alteration of a metabolic pathway
bypasses a reaction inhibited by an antimicrobial agent that occurs in other sulfonamide-resistant bacteria
What happens when a person does not finish their prescription of antibiotics
if this occurs, a more serious infection can develop. By not finishing the antibiotic you leave the most resistant organisms alive, allowing them to multiply leading to an infection that will be difficulty or impossible to cure using the same antibiotic
Kirby - Bauer Method
a standard quantity of the causative organism is uniformly spread over an agar plate. Then several filter paper disks impregnated with specific concentrations of selected chemotherapeutic agents are placed on the agar surface. Finally, the culture with the antibiotic disks is incubated. Clear areas, called zones of inhibition appear on the agar around disks where the agents inhibit the organism. The size of a zone of inhibition is not necessarily a measure of the degree of inhibition because of differences in the diffusion rates of chemotherapeutic agents. One can measure the zones and look at a chart to see whether the drugs are sensitive, moderately sensitive, or resistant to the drug
Dilution method
a standardized microdilution plate with shallow wells that contain increasing dilutions (decreasing concentrations) of selected antibiotics in a broth is inocultaed with a test bacterium. The lowest concentration that prevents growth is known as the minimum inhibitory concentration (MIC) for a particular agent acting on a specific microorganism.
Minimum Bactericidal Concentration (MBC) test
Samples from tubes that show no growth but that might contain inhibited organisms can be used to inoculate broth that contains no chemotheraputic agent. in this test, the lowest concentration of the chemotheraputic agent that yields no growth following a second inocultaion, or subculturing, is the MBC
Characteristics of an ideal antimicrobial agent
- solubility in body fluids
- selective toxicity
- toxicity is not easily altered
- non-allergenic
- stability
- Resistance by microorganisms not easily acquired
- long shelf life
- reasonable cost
Why is it so hard to produce agents against fungi, viral, protozoan, and helminthic organisms?
Treatment of worm infections and viruses are especially difficult because what damages the parasite will also damage the host. Because fungi are eukaryotes and thus similar to human cells, antifungal treatment often causes toxic side effects.
Antifungal agents
clotrimazole, miconazole, amphotericin B, nystatin, griseofulvin, flucytosine
Antiviral agents
idoxuridine, ganciclovir, vidarabine, ribavirin, acyclovir, amantadine, AZT
Antiprotozoan agents
Quinine, chloroquine, primaquine, pyrimethamine, metronidazole
Antihelminthic Agents
niclosamide, piperazine, mebendazole, Ivermectin
