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