Antimicrobial therapy intro (lecture 2)

traditional lab tests

direct microscopic examination (gram stain and morphology)

Cultures

Rapid tests

antibody/antigen/nucleic acid detection

Two largest classes of bacterial pathogens

gram positive cocci

Gram negative rods

Gram positive cocci

staphylococcus, streptococcus, enteroccoccus

Gram negative rods

e.coli, enterobacter, klebsiella

Importance of pure monocultures

definitive diagnosis relies on specific monoculture of a suspected pathogen from blood or wound

Decision tree analysis

1) gram staining

2) evaluate the growth of organisms in selective media

3) assessing chemical characteristics (fermentation properties)

4) testing for the presence or absence of specific enzymes

Gram positive cocci typically infect

skin, soft tissue, heart, lung, bones, joints, hardware, indwelling lines

Gram negative rods typically infect

Lung, any intraabdominal, organ

Anaerobes typically infect

lung, oral cavity, intraabdominal organ

Atypicals infect

the lung

antibiotics are classified based on

class and spectrum and microorganisms it kills

Narrow spectrum

effective against relatively few bacteria, less likely to cause gross disruptions, considered best choice when available

Extended-spectrum

drugs that have activity in additional species no covered by most members of a class

Broad spectrum

effective against many or most bacteria, most commonly used in empiric treatment

Process for choosing correct antibiotic

1) initial clinical assessment

2) empiric therapy

3) microbiological testing

4) definitive therapy

5) pharmacokinetics and pharmacodynamics

6)resistance considerations

7) ongoing monitoring

Prophylactic therapy

treatment given to prevent an infection that has not yet developed

Bacteriostatic

reduced growth but does not necessarily kill

Bactericidal

kills bacteria

Minimul inhibitory concentration

determine lowest concentration of antibiotic that inhibits growth, want concentration of antibiotic in tissue to be above mic

Clinical break points

MIC of an antibiotic that’s effective in treating an infectious disease from a particular strain in 80% of cases

Susceptible

MIC is less than breakpoint for organism

Intermediate

MIC is at breakpoint

Resistant

MIC is greater than breakpoint

MIC is not comparable

between drugs

Minimal bactericidal concentration

lowest concentration of the drug that kill 99.9% of total initially viable cells

Antibiotic dosing is based on

pharmacokinetic and pharmacodynamics

Pharmacokinetic

ADME

adsorption, distribution, metabolism, excretion

Pharmacodynamics

How antibiotics interact with organisms to kill them

Definitive therapy

Known organism susceptibility; agents that are safe, effective, narrow in spectrum, cost effective

Post-antibiotic effect

persistent suppression of microbial growth after levels of antibiotic have fallen below MIC