UV light, Disinfectants, Antibiotics

• UV light is used to control microbial growth

• Adjacent thymine molecules DNA cross link to form thymine dimer

• This leads to mutations during the replication of DNA

• #3 – growth , UV light cannot penetrate plastic.

• Disinfectants – antimicrobial agents used on objects – floors. Lysol

• Antiseptics – antimicrobial agents used on living tissue – mouthwash. Listerine

• They inactivate enzymes

• Zone of inhibition – in general larger the zone of inhibition more effective is the antimicrobial agent

• Gram negatives are more resistant than gram positives.

• Substances cannot penetrate the outermembrane.

Antibiotics

• Made by microbes

• Purified by the pharmaceutical companies

• Penicillin

• Mold – Penicillium notatum

• Inhibits the formation of peptidoglycan

• G- - resistant

• G+ - sensitive

• Penicillin – selectively toxic to bacteria. In general, it is not toxic to the host (humans)

• Humans have no peptidoglycan

• Chloramphenicol – Streptomyces• Inhibits protein synthesis on the 70S

ribosomes• High concentrations and prolonged use

can cause aplastic anemia• Streptomyces• Tetracycline, Streptomycin, erythromycin• Erythromycin – cannot penetrate the outer

membrane

• Gentamicin – Micromonospora

• Inhibits protein synthesis on the 70S ribosomes.

• Sulfanilamide – synthetic drug

• Inhibits folic acid synthesis