Antimicrobial Flashcards
Antimicrobials
Drugs that kill or inhibit the growth of microorganisms
Antibiotics
specifically describe a natural substance produced by one microorganism that suppresses the growth of another microorganism
What are antimicrobials classified according to?
- the type of microorganism it fights
- Whether it kills the microorganism or only prevents it from replicating & proliferating
-cidal
Drugs that kill the named microorganism
Bactericidal, fungicidal, virucidal
-static
Drugs that inhibit replication
Do not directly kill the microorganism
Bacteriostatic, fungistatic
What must time-dependent bacteriostatic and bactericidal drugs maintain?
Concentrations constantly above the minimum inhibitory concentration (MIC)
What are examples of time dependent bacteriostatic drugs?
Chloramphenicol Lincosamide/clindamycin Macrolides Sulfonamides Tetracyclines
What are examples of time-dependent bactericidal drugs?
Cephalosporins
Penicillin family
What are examples of concentration-dependent bactericidal drugs?
Aminoglycosides
Fluoroquinolones
What is the goal of antimicrobial therapy?
To kill or disable pathogens without killing the host
Successful administration of anti-microbials requires the following conditions..
- The microorganism must be susceptible to the antimicrobial drug
- The antimicrobial must be able to reach the site of infection in high enough concentrations to kill or inhibit the microorganism
- The animal must be able to tolerate the required high concentrations of the drug
What is the process of identification and drug susceptibility testing?
Culture and Sensitivity
What does culture and sensitivity determine?
The susceptibility of a bacterial strain to certain drugs
How does culture and sensitivity determine the susceptibility of a bacteria to certain drugs?
By determining how much drug it takes to inhibit or kill the bacteria
What happens when the culture and sensitivity is done?
The bacteria are exposed to increasing concentrations of drug to determine the lowest concentration that inhibits the growth of the cultured bacteria
What is the lowest drug concentration needed to inhibit bacterial growth called?
Minimum inhibitory concentration
What is the highest concentration of a drug that can be tolerated by the animal before significant toxicity signs or adverse effects?
Maximum tolerated dose (MTD)
What needs to happen for a drug to be used systemically to treat an infection?
The drug’s MIC needs to be lower than the concentration of the MTD
Resistant
The MIC is higher than the drug’s MTD
Susceptible
The MIC is lower than the MTD
Intermediate resistance or susceptibility
The drug concentrations achieved at the actual infection site may or may not be sufficient to inhibit bacterial growth
What must occur for an anitmicrobial to be effective?
It must be able to be absorbed from the administration site and distributed to the site of infection in sufficient quantity to produce concentrations in excess of the MIC
What is a higher concentration than MIC because the bacteria are not just being held in a static condition but are actually being killed by the drug directly?
Minimum bactericidal concentration (MBC)
What may play a role in overall development or emergence of resistant bacteria in humans?
The misuse of veterinary antibiotics in food animal medicine
How does bacterial resistance typically occur?
As a result of a genetic mutation in the DNA of bacteria
Vertical transmission of resistance
The passing of a resistant genetic trait to the daughter bacteria cells & all subsequent generations of the original bacterium
Horizontal transmission of resistance
Some bacteria make physical contact with another bacterium & transfer the plasmid-containing resistant DNA across the cell membrane
What happens when bacteria develops more than one resistant mechanism?
A multi-drug resistant bacterial strain
What limits bacterial proliferation and keeps the bacterial population below the number needed to produce clinical disease?
- The patient’s immune system
- The bacterial competition for limited available resources
- Other environmental or host factors
What is The elimination of weaker bacteria by low dose or inappropriate administration of antimicrobial drugs?
Selection pressure
What does selection pressure cause?
Resistant population of bacteria to emerge
Selection pressure does not create mutations or speed up the rate at which mutations occur, what does it do?
Helps resistant bacteria proliferate and emerge into a clinical disease that is resistant to treatment
If clients do not follow the instructions to treat their animal with antibiotics, can they facilitate the emergence of resistant bacterial populations?
Yes
Time-dependent drugs
Drugs that are required to remain at high concentrations at the infection site continuously
Does significantly increasing the peak drug concentration well above the MIC for time-dependent drugs increase the effectiveness of these drugs?
No, not by itself, unless the drug concentrations remain above the MIC continuously
For concentration-dependent drugs to be effective they must either…
-Achieve a peak drug concentration far exceeding the MIC
OR
-Maintain a high level of concentration for a longer period of time
What is the continued killing effect in the absence of drug concentration above the MIC and is a concentration-dependent effect?
Post antibiotic effect
What must happen to reduce the emergence of resistant populations of bacteria?
- The appropriate antimicrobial dose must be used
- Full duration of treatment must be completed
What is the presence of a drug, chemical or its metabolites in animal tissues or food products
Residue
Residue results from either…
-Administration of that drug or chemical to an animal
OR
-Contamination of food products during food processing
What must be withdrawn and treatment stopped a specific number of days before the animal can be slaughtered?
Food animal drugs
What does stopping food animal drugs a number of days before the animal can be slaughtered allow for?
enough time for the drug to be excreted from the body & tissue concentrations to drop below the required government-mandated limit
What two effects are caused by low levels of antimicrobials in ingested food?
An allergic reaction to the antimicrobial
Selection for resistant bacteria in the intestinal tract
Antimicrobials generally exert their effects at 5 sites in microorganisms. What are those 5 sites?
- The cell wall
- The cell membrane
- Ribosomes
- Critical enzymes
- Nucleic acids
How do antimicrobials inhibit or kill bacteria?
By interfering with formation of the bacterial cell wall during bacterial cell division
What is a common ingredient in topically applied first aid creams and is an example of an antibiotic that works by damaging the bacterial cell membrane?
Polymyxin B
What are examples of antibiotics that act by combining with ribosomes and disrupting protein synthesis, stopping cell division, and or killing the cell?
Lincosamieds
Macrolides
Tetracyclines
Aminoglycosides
What is an example of a group of antibiotics that work by interfering with critical enzymes needed by pathogenic bacteria to produce essential nutrients or substances they need to survive?
Sulfonamides
What are examples of newer antibiotics that disrupt DNA function by interfering with the enzymes needed for DNA to function, but do not disrupt the DNA sequence itself, and attack specific types of molecular structures found only in bacteria and not mammalian cells?
Fluoroquinolones
Enrofloxacin, Orbifloxacin
