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Culture and Sensitivity, Bacterial Cyclosporine Blood Levels 1333

Culture and Sensitivity, Bacterial
VetBooks.ir Definition Drug Effects

relates with the ability of the compound
Bacterial culture techniques grow (in vitro), growth inhibition around the disk cor- Previous or ongoing antimicrobial administra-
isolate, and characterize potential bacterial to inhibit growth, but true MIC cannot tion may result in false-negative results.
pathogens from biological specimens. Bacterial be determined.
sensitivity (i.e., susceptibility) techniques aid ○ E-test: Commercially available plastic Lab Artifacts
in determination of potential antimicrobial test strips impregnated with gradually • Contamination (during collection by use of
effectiveness against isolated bacterial species. decreasing concentration of antimi- nonsterile containers, prolonged storage at
crobial compounds can be placed on room temperature, or delays in shipment)
Synonyms a plate of growth media streaked with may result in overgrowth.
Culture and susceptibility, C/S bacterial isolate. The strip allows semi- • Delays in culture may result in absent growth.
quantitative determination of the ability • Contaminant organisms may inhibit growth
Physiology of the antimicrobial to inhibit bacterial of more fastidious organisms.
For routine bacterial culture, the biological growth.
specimen is streaked onto a blood and Mac- ○ Automated susceptibility testing systems: Specimen Collection and Handling
Conkey agar culture media and incubated Various commercial systems used in large Fresh tissue or fluid in sterile container;
for 24-48 hours. Resultant bacterial colonies laboratories provide automated susceptibil- culture swab is acceptable for both aerobic and
are isolated and identified. For antimicrobial ity data, usually with an MIC provided. anaerobic culture. Blood specimens should be
susceptibility testing, each bacterial type is ○ Genotypic methods: though not standard, collected in blood specimen vials containing
exposed to various antimicrobials at a variety genotypic methods such as PCR can be growth media. Tubes containing microbial
of concentrations to assess the ability of each used to detect DNA sequences character- preservative are available for urine cultures
to inhibit bacterial growth. istic of antimicrobial resistance. where a delay in plating is anticipated. Consult
laboratory for any specific questions on ideal
Reference Interval Causes of Abnormally High Levels collection and transport conditions.
• Bacterial isolates are identified by genus and/ Infection or contamination by bacteria produces
or species. growth. Relative Cost: $$
• There are multiple ways to determine and
report antibacterial susceptibility. These Next Diagnostic Steps to Consider Pearls
include: if Levels are High • Not all bacteria are easily detected using
○ Broth dilution method: the isolate is Multiple factors beyond sensitivity results must routine bacteria culture techniques. Fastidious
cultured in serial dilutions of antimicrobial be considered when selecting antimicrobials. organisms may need special growth media,
compounds. The lowest concentration of These include likely in vivo response in a given incubation and atmospheric conditions.
antimicrobial that inhibits bacterial growth environment (e.g., purulent material inactivates • Microbial susceptibility is seldom provided
is the Minimum Inhibitory Concentra- some antimicrobial compounds), bioavailability for anaerobic isolates.
tion (MIC). A predetermined range of the drug in target tissue (e.g., beta-lactams • Special media may be appropriate for sample
of acceptable MIC for each pathogen achieve high concentrations in the urinary submission. For example, special blood Laboratory Tests
can be used to classify the organism as bladder), specific host factors (e.g., nephrotoxic culture media contain beads that bind and
susceptible, intermediate, or resistant to a drugs should be avoided in animals with renal inhibit antimicrobial drugs, improving the
given antimicrobial compound. The lower compromise), potential drug interactions or chance of bacterial growth in animals that
the MIC concentration, the more likely toxicities, route of administration, available have received antibiotic treatment.
the pathogen is to be responsive to a given formulations, costs, potential drug toxicities, • MIC in vitro may not predict resolution of
antimicrobial compound. and others. an infection in vivo.
○ Kirby Bauer disk diffusion: a plate of • In some instances, use of a drug with a “high
growth media is evenly streaked with the Causes of Abnormally Low Levels MIC” may be appropriate.
bacterial isolate. Commercially prepared Inhibition of growth by antimicrobial drugs or • For infections resistant to many antimicrobial
disks impregnated with standard con- other molecules, overgrowth of other bacteria compounds, consultation with a specialist is
centrations of antimicrobial compounds (pathogenic or contaminants), poorly represen- recommended.
are spaced around the plate, which is tative specimen or mishandling of specimen,
then incubated. The size of the ring of absence of infection AUTHOR: Erin N. Burton, DVM, MS
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP

Cyclosporine Blood Levels

Definition Physiology both trough and peak samples. Cyclosporine
Cyclosporine is a potent immunosuppressant Cyclosporine is used to treat a variety is metabolized in the liver, so patients with
drug that impairs T-lymphocyte activation and of autoimmune disorders (dermatologic, liver disease may require dose adjustments. At
the downstream immune responses of several hematologic), as well as perianal fistulas. least 50% of cyclosporine in blood is within
inflammatory cells; blood levels are measured Variable pharmacokinetics requires routine erythrocytes.
as a marker for reaching a therapeutic target. monitoring of blood levels, often including
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