CHAPTER7 MICROBIAL CONTROL

Microbial contamination

• Sepsis refers to microbial contamination. Also a term for blood infection/septicemia • Asepsis is the absence of significant contamination. • Aseptic surgery techniques prevent microbial contamination of wounds.

Terminology • Bacteriostatic: inhibits bacterial growth • Bactericidal: something capable of killing bacteria • Antiseptic: an agent that is used to inhibit/kill bacterial growth on skin and mucus membranes • Disinfectant: an agent that is used to inhibit/kill bacterial growth on inanimate objects

1

Terminology • Sterilization: Removal of all microbial life • Commercial Sterilization: Killing C. botulinum endospores • Degerming: Removal of microbes from a limited area • Sanitization: Lower microbial counts to safe public health standards • Biocide/Germicide: Kills microbes

History behind microbial control • Joseph Lister was the first to introduce the use of carbolic acid to reduce bacterial infections in hospitals (1860s) • Ignatz Semmelweis regarded as the “Father of Infection Control”, physicians used chlorinated lime to cleanse hands (1850s)

2

What factors influence the success of microbial control? • Is the organism an endospore former? • What type of organism are you targeting? • What type of environment are you treating?

Bacteria die at a constant logarithmic rate

Figure 7.1a

Effectiveness of treatment • Number of microbes • Environment (organic matter, temperature, biofilms) • Time of exposure • Microbial characteristic Figure 7.1b

3

Are all bacteria equally sensitive?

What parts of a bacterial cell are sensitive to physical treatments and chemicals? • Plasma membrane • DNA and proteins

Physical Methods of Microbial Control • Heat – Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min. – Thermal death time (TDT): Time to kill all cells in a culture – Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature

4

Physical Methods • Heat – Dry: kills by oxidation (incineration, flaming, hot air) – Moist: promotes coagulation of proteins • Boiling (100oC) • Autoclave(121oC, 15lbs/sq inch) • Pasteurization reduces spoilage organisms and pathogens • Equivalent treatments – Classic: 63°C for 30 min – High-temperature short-time/HTST: 72°C for 15 sec – Ultra-high-temperature/UHT: 140°C for