Bacteriology 14: Principles of treatment of bacterial infections Flashcards
What is the general principles of treatment of bacterial infections?
Correctly diagnose presence of a bacterial infections!
**Determine what is the underlying host **
(tissue) compromise and address this
“stressor” (= predisposing factor) in
your treatment plan, for example:
treat sarcoptic mange
treat urolithiasis
Determine the likely causative agent or agents
-If it is bacteria that are predictable susceptible to an antibiotic, or infection commonly responds to routine antibiotics
- may not need to positively identify bacteria or do a
susceptibility test (= empirical therapy)
-If it is bacteria that are not predictably sensitive, then need to collect a sample and submit for culture and susceptibility testing
Administer appropriate antibiotic
-Judicious use of antibiotics
Include appropriate ancillary treatments
-Debride/lavage any necrotic tissues*
-Drain any abscesses*
-Promote innate defense mechanisms
ex.: bronchodilators, nebulization, fluid therapy
Antibiotic nomenclature?
Antimicrobials against little life
-bacteria, viruses, fungi, protozoa
Antibacterials LARGEST class
-“Natural” and synthetic/semisynthetic
Antibiotics
-substance made by a microorganism that acts upon another microorganism
Antibiotics are always __________, but an _____________ is NOT always an Antibiotic!
ANTIBACTERIAL
ANTIBACTERIAL
Are we making more or less antibiotics in comparison to history?
LESS
Why is it stressful that we are not getting new antibiotics?
Due to there be an increase of antibiotic resistance
What are the 4 basic mechanisms of resistance?
Prevent entry of drug
Pump drug out of the bacteria
Inactive drug (modification/degradation)
Change target site for the drug
What kind of resistance do we have?
Intrinsic and Acquired resistance
How does Intrinsic resistance work?
BActer’a natural ability to resist effects
All bacteria of a certain type posses this ability
-Aminoglycosides for anaerobes
-Metronidazole for aerobes
-Sulfonamides, trimethoprim, tetracyclines,
chloramphenicol for Pseudomonas aeuruginosa
- A normal *P. auruginosa will look “ multi- drug resistant”
Acquired Resistance works by?
The bacteria gains the ability to resist a drug, where it was previously susceptible
Tends to be found in some strains/subtypes of a bacterial species
Multiple mechanisms by which bacteria can acquire resistance
-Mutation
-Acquisition of resistance genes
What are the mechanisms of Acquired resistance?
Mutation of genes that code for physiological processes
-mycobacterium tuberculosis & rifamin - rpoB
Acquisition of foreign genes that encode resistance
-Horizontal gene exchage which are then passed on vertically
- MRSA- mecA
Antimicrobial Susceptibility testing in small animals?
Antimicrobial accounted for 51% of prescriptions
52% of animals diagnosed with a new disease were prescribed antimicrobials
Culture and susceptibility testing in SA emergency & Critical Care patients
given too often ~many times they do NOT have infection
Is susceptibility tests invivo or invitro test?
INVITRO
When are susceptibility tests indicated?
Young or critical ill patients
-decreased immune defenses
Site of infection (should be) sterile
-specially when it is difficult to treat
-or have a significant impact on the health of a patient
Bacterial pathogens whose susceptibility canNOT be reliably predicted or if rapid development of resistance is anticipated
-ex. E.coli, S. aureus, Klebsiella spp., and enterobacter spp
Failure of presumptive or confirmed bacterial infection to respond to therapy
Is there times we should NOT do susceptibility testing?
YES
Predictably susceptible
-beta-hemolytic streo.
High level of efficacy of empirical therapy
-treatment of uncomplicated cystitis in dogs
If have multiple bacteria isolated from abscesses or wounds
Testing of non-pathogenic normal flora is meaningless
-if isolated, it is because the was suboptimal sample collection
Testing the susceptibility of (many) strict anaerobes
-difficult and most anaerobes are predicatbly sensitive to a range of antimicrobials, penicillin, metro, and clindamycin
How do we preform these tests preformed?
Agar Disk Diffusion
-kirby bauer modification
Broth Dilution tests
-broth microdilution most common
Gradient Dilution tests
ALL should be interpreted by clinical and laboratory standards
Agar Disc diffusion commonly used?
YES
Broth microdilution directly measure what?
MIC (Minimum inhibitory concentration)
Two-fold dilutions of antimicrobials are inoculated in a 96 well plate
-the concentrations represent serum concentrations of the antimicrobial in the patient when the drug is administered at recommended dosages
The MIC is the lowest concentration of the
antimicrobial agent that completely inhibits growth of the organism (determined visually)
What are the advantages of dilution susceptibility systems?
MIC of the bacteria for the antimicrobial can be
determined
May be used to optimize antimicrobial therapy by
application of pharmacokinetic and pharmacodynamic
principles
- You usually need a pharmacologist to help you do
this
What are the limitations of both systems?
Interpretive criteria to establish susceptibility breakpoints are available for only a small number of antimicrobial drugs IN ANIMALS!
In vitro susceptibility testing can be used to reasonably predict in vivo _________ of a
particular antimicrobial BUT ONLY if the ____________ of these tests are understood & applied
Efficacy
Limitations
Are the MIC values derived from susceptibility tests are ___________ _____________ _____, rather they are ____________ to “susceptible”, “resistant” or “intermediate” based on ____________ __________
Rarely directly used
Translated
Breakpoint values
Breakpoints are established based on?
Obtainable SERUM concentrations of the drug & based on PK/PD data
What does it mean when your organism IS susceptible to a drug?
Treatment with this drug using standard label or recommended doses has high probability of a cure
What does it mean when your organism is resistant to a drug?
Treatment with this drug is associated with treatment failure regardless of the dose administered or location of the infection
Function of either:
-A specific resistance mechanisms of the bacterial
strain
-Low concentrations of drug in a host species
