Chapter 10 - Antimicrobials Flashcards
Antimicrobials
Drugs that kill or inhibit the growth of microorganisms, or microbes, such as bacteria, protozoa, viruses, and fungi
Antibiotic
Often used interchangeably with antimicrobial - but specifically antibiotics describe a natural substance produced by one microorganism that suppresses growth of another microorganism
Spectrum of Activity
Antibiotics are classified according to the type of microorganism it fights
The suffix “ -cidal “ means ….
Drugs that kill the microorganism
The suffix “ -static “ means ….
Drugs that inhibit replication and proliferating of microorganisms but do not directly kill them
Pathogens
Disease-causing organisms
Bacteriostatic Drugs
Temporarily inhibit the growth of bacteria, once the drug is removed the organism can begin to multiply again
Because of their mode of action, do bacteriostatic drugs rely more on that than the animals immune system to fight systemic infections?
Bacteriostatic drugs depend far more on the animals functional immune system to ultimately defeat the organism
What is the goal of antimicrobial therapy?
To kill or disable pathogens without killing the host
What are the 3 things required for successful treatment with antimicrobial’s?
1) Microorganism must be susceptible to the drug
2) Drug must be able to reach the site of infection in high enough concentrations to kill or inhibit the microorganism
3) Animal must be able to tolerate the required high concentrations of the drug
What are some of the less essential (but still important) conditions to choosing an appropriate antimicrobial treatment?
- Client compliance (following dosing instructions)
- Ease of administration
- Convenient dosage interval
- Dose form
- Cost
Culture
Grow
Process of identification and drug susceptibility testing is referred to as what?
Culture and sensitivity
What does a culture and sensitivity test determine?
Susceptibility of of a bacterial strain to certain drugs by determining how much drug it takes to inhibit or kill the bacteria
The lowest drug concentration needed to inhibit bacterial growth is called what?
Drug Minimum Inhibitory Concentration (MIC)
The highest concentration of drug that can be tolerated by the animal before significant toxicity signs or adverse effects occur is referred to as what?
Maximum Tolerated Dose (MTD) drug concentration
Resistant
If a drug’s MIC is more than the MTD, the microorganism is resistant to the drug
Susceptible
If a drug’s MIC is less than the MTD, the microorganism is susceptible to the drug
Means the drug’s MIC is close to the MTD.
Intermediate Resistance or Susceptibility
Breakpoints
Mark a drugs MIC that differentiates between when a bacterial strain is considered susceptible, intermediate susceptible or resistant to that particular drug
True or False
Unless the antimicrobials can reach the infection site at the needed concentrations to inhibit the bacteria, the antimicrobial will be ineffective
TRUE
Minimum Bactericidal Concentration (MBC)
- Used to describe the ability of a drug to actually kill, versus inhibit the growth of a bacterial species.
- MBC concentration is typically higher than the MIC because they are not being held in a static condition, they are being killed
Resistance
Bacterial and other microorganisms have developed the ability to survive in the presence of antimicrobial drugs designed to kill them
What is the monitoring system the CDC has in place to track changes in bacterial susceptibility and resistance in the US?
National Antimicrobial Resistance Monitoring System (NARMS)
What other groups does NARMS work with besides the CDC to collect its data to track bacterial susceptibility and resistances?
- State and local health departments
- FDA (Food and Drug Administration)
- USDA ( US Department of Agriculture)
How does bacterial resistance occur?
Typically resistance occurs as the result of a genetic mutation in the Deoxyribonucleic Acid (DNA) of bacteria
Vertical Transmission of Resistance
Passing of this resistant genetic trait to the daughter cells and all subsequent generations of the original bacterium
Plasmid
- Extrachromosomal self-replicating structure found in bacterial cells that carries genes for a variety of functions
- Can be transferred from one cell to another by conjugation and by transduction
Horizontal Transmission or Resistance
Occurs when some bacteria make physical contact with another bacterium and transfer plasmid-containing resistant DNA across a cell membrane
Besides Vertical and Horizontal transmission list 2 other ways cells can transfer DNA
1) Pick up DNA with resistant genes left in the environment after death and lysis of another bacterial cell
2) Receive resistant DNA by a bacterial virus (bacteriophage) that transfers DNA from one bacterium to another
True of False
If a low dose of antibiotic is administered, only the weakest bacteria are going to be inhibited, while all the more resistant bacteria to the drug will survive
TRUE
Selection Pressure
Does not create mutations or speed up the rate at which mutations occur, it only helps resistant bacterial proliferate and emerge into a clinical disease that is resistant to treatment
Bacteriostatic drugs that are required to remain at high concentrations at the infection site continuously to be effective in eliminating bacterial infections
Time Dependent Drugs
Bactericidal agents must either achieve a peak drug concentration far exceeding the MIC or maintain a high level of concentration for a longer period of time to be maximally effective
Concentration Dependent Drugs
Post-Antibiotic Effect
Continued killing effect in the absence of drug concentrations above the MIC (concentration dependent effect)
Residue
Presence of a drug, chemical, or its metabolites in animal tissues or food products (caused by administration directly to animal or contamination during food processing)
What are the two effects that exposure to low levels of antimicrobials from ingested food can cause?
1) Allergic reaction (hypersensitivity) to the antimicrobial
2) Selection for resistant bacteria in the intestinal tract
Gut Flora
Composition of bacteria and protozoa in the intestinal tract
List the 5 sites antimicrobials exert their effects on microorganisms
1) Cell Wall
2) Cell Membrane
3) Ribosomes
4) Critical Enzymes or Metabolites
5) Nucleic Acid
True or False
Antimicrobials that interfere with bacterial cell wall formation only work while the wall is forming during bacterial cell division
TRUE
If these drugs are used once the cell wall is constructed then the microorganism is not readily affected by the antimicrobial drugs
Bacteriostatic Drugs
Biological or chemical agent that stops bacteria from reproducing
What are the 2 drug classes of antimicrobials that act by disruption of new cell wall formation?
1) Penicillin
2) Cephalosporins
When antimicrobials attack and damage the cell membrane what occurs?
Membrane becomes leaky, allowing either the antimicrobial drug molecules to more readily enter the bacterial or allowing vital cytoplasmic components to escape
True or False
Antimicrobials that act by damaging the cell wall can only work when the cell membrane is dividing
FALSE
These antimicrobials can exert their effect on both dividing or static (non-dividing) bacteria
This is a common ingredient in topically applied first aid creams and it works by damaging the cell membrane
Polymyxin B
List 2 of the antimicrobials that act by blocking production of essential proteins (which causes the cell to stop dividing or die)
1) Lincosamides
2) Macrolides
3) Tetracyclines
4) Aminoglycosides
What antimicrobials work by interfering with critical enzymes needed by pathogenic bacterial to produce essential nutrients or substances they need to survive?
Sulfonamide Antibiotics
What antimicrobials interfere with the production of bacterial nucleic acids (RNA + DNA) altering the ability of the cell to divide or produce critical proteins needed by the cell?
Fluoroquinolones (Enrofloxacin)
Because of a particular ring-like structure in their chemical composition, Penicillin’s are also referred to as what?
Beta-lactum or B-lactam Antibiotics
Besides Penicillins, what is the other group of antibiotics that also has a B-lactam ring?
Cephalosporin Antibiotics
List the broad spectrum aminopenicillins used in vet med
Ampicillin
Amoxicillin
List the Penicillinase-resistant or B-lactamase-resistant Penicillins
Cloxacillin
Dicloxacillin
Oxacillin
Methicillin
List the extended-spectrum penicillins
Ticarcillin
Carbenicillin
Piperacillin
Penicillins are generally effective against many gram- ________ bacteria and a lesser number of gram- ________ bacteria
Gram-positive
Gram-negative
True or False
Penicillins are bacteriostatic
FALSE
Penicillins are bactericidal - so they are only effective against an actively dividing colony of bacterial
What does MRSA stand for?
Methicillin-Resistant Staphylococcus Aureus
Bacteriostatic antimicrobials should not be used simultaneously with with ____________ antibiotics
B-lactam antibiotics (because B-lactam abx need the bacterial colony to be actively replicating)
What are the 3 areas penicillins will typically not reach therapeutic concentrations because of the cellular barriers between the tissue and blood supply
Globe of the eye
Brain
Prostate Gland
Why are penicillins commonly used to treat bacterial cystitis caused by bacterial infection?
Most penicillins are excreted by the kidney intact without being metabolized and are actively transported (secreted) by the renal tubules into the forming urine
Aerobic bacteria
Require oxygen
Anaerobic bacteria
Do not require oxygen
Empiric treatment/therapy
Selection of a particular antimicrobial drug before the results of a culture are returned
Porins
Special capsule openings (like pores)