Chemotherapeutic and Chemical Agents Microbiology 156

Antibiotics Drugs that interfere with bacterial cell metabolism They produce a bacteriocidal or bacteriostatic effect on prokaryote cells

Origin of Antibiotics These are agents that have been synthesized by bacteria or fungi against other organisms Example – Penicillin was isolated from the mold Penicillium notatum. It was first observed by Alexander Fleming and later purified by Howard Florey.

Antibiotics inhibit the growth of other microorganisms

Mode of Action Interfere with the synthesis of the cell wall( peptidoglycans) Disruption of the cell membrane Inhibition of folic acid Interference with protein synthesis Interference with nucleic acid synthesis Ribosomal interference

Two Pioneers in Chemotherapeutic agents

Penicillin – The first Effects the synthesis of the peptidoglycans cell wall Makes the bacteria vulnerable to the phagocytes in the immune system

Chemical structure of antibiotics based upon the original penicillin

Antibiotics from Actinomycetes Actinomycetes are soil bacteria They produce compounds that inhibit other microorganisms Competition for food and space in the soil environment Selman Waksman, Rutgers University, NJ

Streptomycin

Inhibition of bacterial growth by soil bacteria

Pharmacology Synthetic drugs are designed based upon the structure of molecules produced in nature by bacteria They are then tested for their antimicrobial activity – in vitro and in vivo

KirbyBauer The determination of antibiotic sensitivity or resistance Sensitivity – The organisms growth is inhibited by the presence of the antibiotic Resistance – The organism has a means of interfering with the mode of action of the antibiotic

Kirby Bauer Plate bacteria on Mueller Hinton Agar Plate Distribute bacteria evenly over the surface of the agar Place discs impregnated with antibiotic on the agar at indicated spots. Incubate

Determination of antibiotic resistance or sensitivity

Chemical agents Incubate the plates for 24 hours Measure the diameter of the plate to determine efficacy of the chemical agents

Determination of resistance or sensitivity Measure the diameter of the ring around the disc Compare the measurement in mm with the table in your lab manual, page 284. Table 44.2 Record your results in Table on page 287.

Control of Microbial Growth- Growth Curve

Heat- Destruction of bacterial cells Autoclave – heat under pressure C at 15 psi for 15 minutes Boiling For more than 30 minutes

Chemical agents Agent Mechanism of Action Use PeroxygensOxidationsUse in wounds and abrasions AlcoholsProtein denaturationSkin disinfection Organic acidsDisrupt proteins- low pH Used to control moleds DetergentsDisrupts cell membranes Disinfection Halogens derivative Iodine Chlorine Inhibits protein action in bacteria Surface area disinfection

Chemical Agents- Agar Plate sensitivity assay Plate the bacteria by spreading it evenly across the Mueller- Hinton agar. Dip sterile filter discs into chemotherapeutic agents. Carefully place the discs in indicated spots on the agar plate

Chemical agents Torr solution Chlorox solution Mouth wash Lysol solution Other

Determination of activity Measure the zone of inhibition around the disc to determine if the antiseptic or disinfectant had sufficient activity to inhibit the growth of the bacteria in your study

Chemical Agent Activity Assay OrganismAntisepticDisinfectant E. coli SA Other