Control of Microbial Growth

Study Notes

Preventing human disease spread requires controlling microbial growth and abundance.
Laboratory personnel working with pathogens require different levels of control based on pathogen risk.

BSL-1: Standard aseptic technique, open benches, laboratory coat, goggles, and gloves as needed. No major modifications.
BSL-2: Restricted access, face shields in some circumstances, biological safety cabinets, self-closing doors, eyewash stations, and autoclaves for sterilization.
BSL-3: Restricted access, medical surveillance (vaccinations). Staff wear respirators and work in biological safety cabinets. Hands-free sinks, eyewash near exit, and double self-closing and locking doors. Directional airflow.
BSL-4: Full-body protective suits with designated air supply or work within biological safety cabinets with HEPA-filtered exhaust. Air pressure in the suit is higher than outside. Separate building and its own air supply. Decontamination procedures on entry/exit.

Disinfection: Reduces or destroys microbial load on inanimate items using heat or chemicals.
Sanitization: Reduces microbial load to safe public health levels on inanimate items.
Sterilization: Completely eliminates all vegetative cells, endospores, and viruses on inanimate items. Methods include steam (autoclave), chemicals, and radiation.
Antisepsis: Reduces microbial load on skin or tissues using chemicals.
Degerming: Reduces microbial load on skin or tissues through scrubbing and mild chemicals.

Synthetic antimicrobials: Developed from chemicals not found in nature.
Semisynthetic antimicrobials: Chemically modified derivatives of natural antimicrobials (e.g., penicillin).
Bacteriostatic drugs: Cause reversible inhibition of bacterial growth (growth restarts upon drug removal).
Bactericidal drugs: Kill target bacteria.

Narrow-spectrum antimicrobials: target specific bacterial pathogens (some target only gram-positive bacteria).
Broad-spectrum antimicrobials: target a wide variety of bacterial pathogens (both gram-positive and gram-negative).

Kirby-Bauer disk diffusion test: Observe clear circular zones of inhibition around drug-impregnated disks. Measures antibacterial activity.
Dilution tests: Used to determine a drug's minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The MIC is the lowest concentration that inhibits visible growth, and the MBC is the lowest concentration that kills ≥99.9% of the initial inoculum. Dilution tests are done using test tubes or plates.
Etest: A rapid method of determining the MIC of an antibiotic.