Paul Ehrlich worked on developing a synthetic chemical effective against infection-causing cells only
Scientists discovered penicillin in a mold sample
1935
The sulfonamides were introduced
Mechanisms of Action
Interfere with biosynthesis of the bacterial cell wall
Prevent the cells of the invading organism from using substances essential to their growth and development
Interfere with steps involved in protein synthesis
Interfere with DNA synthesis
Alter the permeability of the cell membrane to allow essential cellular components to leak out
Mechanism of Anti-infective Agents
Mechanism of Anti infective Agents
Anti-infective Activity
Anti-infectives vary in their effectiveness against invading organisms
Some are selective: they are effective only for a small number of organisms
Bactericidal: kill the cell
Bacteriostatic: prevent reproduction of the cell
Narrow Spectrum vs Broad Spectrum
Narrow spectrum of activity
Effective against only a few microorganisms with a very specific metabolic pathway or enzyme
Broad spectrum of activity
Useful in treating a wide variety of infections
Human Immune Response
Goal of anti-infective therapy is reduction of the population of the invading organism
Drugs that eliminate all traces of any invading pathogen might be toxic to the host as well
Immune response is a complex process involving chemical mediators, leukocytes, lymphocytes, antibodies, and locally released enzymes and chemicals
Problems With Treating Infections in Immunosuppressed Patients
Anti-infective drugs cannot totally eliminate the pathogen without causing severe toxicity in the host
These patients do not have the immune response in place to deal with even a few invading organisms
Resistance
Anti-infectives act on a specific enzyme system or biological process; many microorganisms that do not act on a specific system are not affected by the particular drug
This is considered natural or intrinsic resistance to that drug
Acquired Resistance
Microorganisms that were once sensitive to the particular drug have begun to develop acquired resistance
This results in serious clinical problems
Ways Resistance Develops
Producing an enzyme that deactivates the antimicrobial drug
Changing cellular permeability to prevent the drug from entering the cell
Altering transport systems to exclude the drug from active transport into the cell
Altering binding sites on the membranes or ribosomes, which then no longer accept the drug
Producing a chemical that acts as an antagonist to the drug
Preventing Resistance
Limit the use of antimicrobial agents to the treatment of specific pathogens sensitive to the drug being used
Make sure doses are high enough, and the duration of drug therapy long enough
Be cautious about the indiscriminate use of anti-infectives
Identification of the Pathogen
Identification of the infecting pathogen is done by culture
A culture of a tissue sample from the infected area is done
A swab of infected tissue is allowed to grow on an agar plate
Staining techniques and microscopic examination identify the bacterium
Stool can be examined for ova and parasites
Sensitivity of Pathogen
Shows which drugs are capable of controlling the particular microorganism
Important to be done for microorganisms that have known resistant strains
Along with a culture, identifies the pathogen and appropriate drug for treatment
