Lecture 4: Control of Microbial Growth PDF

Control of Microbial Growth Prof. Dr. Wael Nabil Hozzein  Why? To prevent the spread of human disease, it is necessary to control the growth and abundance of microbes in or on various items For researchers or laboratory personnel working with pathogens, the risks associa...

Control of Microbial Growth Prof. Dr. Wael Nabil Hozzein  Why? To prevent the spread of human disease, it is necessary to control the growth and abundance of microbes in or on various items For researchers or laboratory personnel working with pathogens, the risks associated with specific pathogens determine the levels of control required. Laboratory Biological Safety Levels  Laboratory Biological Safety Levels - BSL-1: Laboratory workers use standard aseptic technique and may work at an open laboratory bench or table, wearing a laboratory coat, goggles, and gloves, as needed. Other than a sink for handwashing and doors to separate the laboratory from the rest of the building, no additional modifications are needed. - BSL-2 laboratories require additional precautions including restricted access; a face shield in some circumstances; and the use of biological safety cabinets. BSL-2 laboratories are equipped with self-closing doors, an eyewash station, and an autoclave for sterilizing materials before use or disposal.  Laboratory Biological Safety Levels - BSL-3 laboratories require restricted access. Laboratory workers are under medical surveillance, possibly receiving vaccinations for the microbes with which they work. Laboratory personnel in BSL-3 laboratories must also wear a respirator and work with microbes in a biological safety cabinet at all times. BSL-3 laboratories require a hands-free sink, an eyewash station near the exit, and two sets of self-closing and locking doors at the entrance. These laboratories are equipped with directional airflow, meaning that clean air is pulled through the laboratory from clean areas to potentially contaminated areas.  Laboratory Biological Safety Levels - Laboratory workers in BSL-4 facilities must also change their clothing on entering the laboratory, shower on exiting, and decontaminate all material on exiting. While working in the laboratory, they must either wear a full- body protective suit with a designated air supply or conduct all work within a biological safety cabinet with a high-efficiency particulate air (HEPA)-filtered air supply and a double HEPA-filtered exhaust. If wearing a suit, the air pressure within the suit must be higher than that outside the suit, so that if a leak in the suit occurs, laboratory air that may be contaminated cannot be drawn into the suit. The laboratory itself must be located in a separate building and have its own air supply. Methods for controlling microbial growth Antimicrobial Drugs  Sources of antimicrobials A synthetic antimicrobial is a drug that is developed from a chemical not found in nature The discovery of penicillin, the first natural antibiotic A semisynthetic antimicrobial is a chemically modified derivative of a natural antibiotic  Bacteriostatic Versus Bactericidal Bacteriostatic drugs cause a reversible inhibition of growth, with bacterial growth restarting after elimination of the drug Bactericidal drugs kill their target bacteria  Spectrum of Activity A narrow-spectrum antimicrobial targets only specific bacterial pathogens, some narrow-spectrum drugs only target gram-positive bacteria A broad-spectrum antimicrobial targets a wide variety of bacterial pathogens, including both gram- positive and gram-negative species Testing the effectiveness of antimicrobials The Kirby-Bauer disk diffusion test: Antibacterial activity is observed as a clear circular zone of inhibition around the drug- impregnated disk  Dilution Tests Antibacterial dilution tests can be used to determine a particular drug’s minimal inhibitory concentration (MIC), the lowest concentration of drug that inhibits visible bacterial growth, and minimal bactericidal concentration (MBC), the lowest drug concentration that kills ≥99.9% of the starting inoculum The Etest can be used to determine the MIC of an antibiotic. In this Etest, vancomycin is shown to have a MIC of 1.5 μg/mL against Staphylococcus aureus.