Decontamination
Laboratory acquired infections can be transmitted either through direct methods (e.g. needle stick with a contaminated needle) or indirectly through the environment (e.g. aerosols, contaminated work surfaces). Environmental transmission is dependent upon three factors: a sufficiently virulent organism, a high enough concentration to give an infectious dose, and a mechanism by which the pathogen gets from the environment into the host.
Decontamination renders an item (floor, bench top, device etc.) safe to handle by reducing the level of microbial contamination such that transmission is unlikely to occur (reduces the number of organisms below the threshold infectious dose). Decontamination in a microbiology laboratory is usually accomplished by steam sterilization or autoclaving. Other kinds of decontamination can be as simple as using soap and water for hand washing.
The purpose of decontamination is to reduce the microbial numbers to break the transmission cycle and one effective way to do this is through cleaning. Sterilization, disinfection and antisepsis are all forms of decontamination.
Sterile means that an item is completely free of ALL LIVING microorganisms and viruses. The process of sterilization can be accomplished by heat, ethylene oxide gas, hydrogen peroxide gas, plasma, ozone and radiation. These methods are effective enough to kill even high numbers of bacterial endospores.
Disinfection is not as effective as sterilization. Some organisms such as bacterial endospores may remain. Disinfection can also be affected by the number of organisms present, the amount of organic material (blood, feces, soil) present, the type of inanimate object to be disinfected, and the temperature. The effectiveness of chemical germicides is determined by how well each kills vegetative bacteria, viruses, fungi, Mycobacterium tuberculosis and spores.
Antisepsis is the term used to describe the reduction of microorganisms from living tissue. Typically bacterial endospores are not destroyed in this process.
The following table taken from the BMBL demonstrates the order of resistance to germicidal chemicals.
DESCENDING ORDER OF RESISTANCE TO GERMICIDAL CHEMICALS
BACTERIAL SPORES
Bacillus subtilis, Clostridium sporogenes
⇓
MYCOBACTERIA
Mycobacterium tuberculosis var. bovis, Nontuberculous mycobacteria
⇓
NONLIPID OR SMALL VIRUSES
Poliovirus, Coxackievirus, Rhinovirus
⇓
FUNGI
Trichophyton spp., Cryptococcus spp., Candida spp.
⇓
VEGETATIVE BACTERIA
Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella choleraesuis, Enterococci
⇓
LIPID OR MEDIUM-SIZE VIRUSES
Herpes simplex virus, Cytomegalovirus, Respiratory syncytial virus, HBV,
HCV, HIV, Hantavirus, Ebola virus
Here are three links to tables from The Center for Food Security and Public Health, Iowa State University that summarize what is currently known about disinfectants and their use.
Characteristics of Certain Disinfectants
Antimicrobial Spectrum Disinfectants
Special Note: Prions are characterized by resistance to conventional inactivation procedures including irradiation, boiling, dry heat and chemicals. The safest way to destroy infectivity is to incinerate the contaminated items including animal carcasses and tissues. If the item is not disposable, then the combination of sodium hypochlorite or NaOH combined with the moist heat of steam sterilization is effective.