Disinfection and Sterilization,For the course of Medical Microbiology for MBBS foreign students, Class 2006/2011, SYSUSeptember 18, 2007Mengfeng Li （黎孟枫）, M.D. Department of Microbiology, Zhongshan School of Medicine, SYSU, Guangzhou, China limfmail.sysu.edu.cn,Medical Microbiology,Early needs and success for disinfection (Early 1800s) a historic story,By mid-1800s, almost half of post-operative patients died of sepsis (then called “hospital disease”). A common report by surgeons was: operation successful but patient died.A hypothesis: exposing moist body tissue to oxygen sepsis; best prevention: keeping air away from wounds by means of plasters, collodion or resins.Having tried methods to encourage clean healing with no success, surgeon Joseph Lister discarded the concept of direct infection by bad air but postulated that sepsis might be caused by a pollen-like dust, although he did not know yet the “dust” was living microbes. When Louis Pasteur suggested the presence of living organisms in the air, Lister made the connection with wound sepsis: the microbes in the air were likely causing the sepsis and should be destroyed before they entered the wound.Lister had previously heard that carbolic acid was used to treat sewage, and that fields treated with the affluent were freed of a parasite causing disease in cattle. He then began to clean wounds and dress them with carbolic acid,Joseph Lister operated with carbolic acid (石炭酸）spray,The milestone: case of James Greenlees,-Aug. 12, 1865, James Greenlees, 11-year-old -Struck by a horse-drown cart -Compound fractures -Taken to Royal Infirmary -Under the care of Joseph Lister,Why disinfection and sterilization?,Contagious diseases Hospital infection (e.g., OR, ID ward) or other opportunistic infection Lab contamination Etc. Microbes: usually easy to grow in environment; but also can be inhibited or killed by certain environmental (physical or chemical) factors/conditions.,Terminology,Disinfection 消毒 Sterilization 灭菌 Bacteriostasis 抑菌 Antisepsis 防腐 Asepsis 无菌,Disinfection（消毒）,Process of reducing or eliminating living pathogenic microorganisms in or on materials, so they are no longer a health hazard.For example: use of alcohol before drug injection.,Sterilization（灭菌）,Process of destroying all microbial forms. A sterile object is one free of all microbial forms, including bacterial spores.More thorough than disinfection,Bacteriostasis（抑菌）,Process of inhibiting the growth of microorganisms, in vivo (mostly) or in vitro. For example: bacteriostatic antibiotics,Antisepsis （防腐）,Process of inhibiting or preventing growth of microbes, mostly in vitro and not bactericidal or sporicidal (杀芽胞的 )For example: use of chemical agents on skin, other living tissues or food/beverage.,Asepsis（无菌）,A state where no living microorganism exists. For example: OR (Operating Room),Controlling Microorganisms with Physical Conditions,High Temperature (heat) Radiation Ultrasound Filtration Low Temperature Desiccation（干燥）,High Temperature Dry heat and Moist heat protein denaturation and clotting; DNA strand breakdown,.,Dry heat：protein oxidationIncineration（焚烧） most thorough (500) disposals and corpesFlaming (burner)（烧灼） test tube opening, transferring loopHot air sterilization/Baking（干烤） 160-170, 2h Glassware, china, syringes, needles, etcInfrared heat: similar to baking,Moist heat：denaturing proteins and melt lipids Autoclaving（高压蒸汽灭菌） Most commonly used and effective 121 (103.4kPa), 15-20min killing both vegetative organisms and endospores Boiling 100 (105 with 2% Na2CO2) , 15-20min cidal for vegetative cells but not necessarily sporesRegular Steam (Arnold Sterilizer) 100 , 15-20min cidal for vegetative cells but not necessarily spores,Pasteurization（巴氏消毒法） to kill pathogens in readily perishable objects (milk, wine) flash method (瞬间法): 71.6, 15s holding method (持续法): 62.9, 30 minFractional sterilization（间歇蒸气灭菌法） alternating exposure and cooling time for a consecutive period:Steam heating (100, 30 min) 30 for endospores to germinate 100, 30 min to kill germinated endospores 30-37 overnight for remaining endospores to germinate 100, 60 min to kill last remaining germinated endospores for sugar- or milk-containing culture media,Moist Heat vs Dry Heat,Moist heat Dry heatPenetrating potency higher lowerTemp for protein clotting lower higher Extra heat released yes nofrom condensation,Sterilizing potency: Moist heat Dry heat,Radiation,Ultraviolet (UV) radiation mechanism: blockage of DNA replication by forming thymidine dimmers microbicidal activity of UV depends on: length of exposure wavelength: 200-300 nm, with the best effect of 265-266nm bulb life (4000hr) very poor penetrating power for air or surface disinfection(OR, ID ward, labs) causing eye damage, burnsand mutation in skin cells,Ionizing Radiation（电离辐射） X-rays, gamma rays and high-speed electrons generating more energy and penetrating power than UV to sterilize pharmaceuticals, disposable medical supplies (e.g., syringes, gloves, catheters, sutures) and foodsMicrowave penetrating non-metal materials (glass, plastics, china),