Microbicides & Disinfection

Global Campaign for Microbicides    Alliance for Microbicide Development    International Partnership for Microbicides   

 Prince Leopold Institute of Tropical Medicine    Reprotect; products to protect reproductive health   

Companies involved with Microbicidal Development    Indevus Pharmaceuticals  (HIV microbicidal products) 

Sterilization is the killing or removal of all microorganisms, including spores. One can sterilize by --incineration, --filtration, --heat (Pasteurization is the heating of liquids to a temperature that inactivates important pathogens, but below that needed for sterilization), --gas, --radiation, --chemical

Disinfection is the killing of many, but not all microorganisms. Disinfectants are generally chemicals used on inanimate objects. However, antiseptics are disinfectants used on body surfaces. Type of disinfectants include:

• phenol was the original agent used to disinfect. So the effectivness of all other agents are based on phenol. (i.e., ratio of the [phenol] to the [agent] required to cause the same amount of killing under the same standard conditions. Phenol is a protein denaturant. Two types of phenols are hexachlorophene and chlorhexidine which alters membrane permeability.

• alcohols are protein denaturants. Ethanol is 70% alchohol and isopropyl is 95%. Activity of alchohol is more active in the presence of water (70% alcohol is more effective than 95% alcohol).

• halogens oxidize. 2 types are 1) iodine and 2) chlorine (5% solution of sodium hypochlorite)

• surfactants are hydrophobic and hydrophilic groups that solubilize

Antimicrobials exhibit selective or greater toxicity to parasites and have many modes of activity. The Minimum inhibitory concentration (MIC) refers to the tube showing the least amount of agent with no growth after dilutions of the agent in tubes with a constant amount of bacterial isolate. How does one test for antimicrobicity? One way is Disc diffusion where you seed a bacterial isolate over an agar plate and place discs containing antimicrobial agents on the agar. A zone of inhibition develops if the organisms is susceptible to the agent.

Antimicrobial resistance is due to resistant strains found in a small proportion of a population which are selected out. Resistance is mediated primarily by large scale use of antibiotics.

What makes a good sterilization agent or disinfectant? Well the best agent is one which leaves the least number of organisms. The number of survivors (N) is inversely proportional to the concentration of the agent and to the time (T) of application of the agent.

Some of the various methodologies used to sterilize or disinfect include the following:

• flame

• filtration: pore size should be less than 22um for bacteria

• moist-heat autoclaving which is exposure to steam at 121C under pressure of 15 lb/square inch for 15 minutes

• flash autoclaving is steam at 134c for 3 minutes

• boiling does not kill spores

• dry heat for 180 c for 2 hours

• ethylene oxide autoclaving is used for plastics and other heat sensitive materials. It uses gas alkylate proteins and nucleic acids

• radiation which can include UV and X-ray

• chemicals