Microbicides and sterilization

Websites of Interest:

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

Introduction/Definitions:

Sterilization is the killing or removal of all microorganisms, including spores. One can sterilize by the following methods: 1) incineration, 2) filtration, 3) heat such as boiling does not kill spores, dry heat for 180 c for 2 hours. 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 (Pasteurization is the heating of liquids to a temperature that inactivates important pathogens, but below that needed for sterilization), 4) gas, ethylene oxide autoclaving is used for plastics and other heat sensitive materials. It uses gas alkylate proteins and nucleic acids 5) radiation, which can include UV and X-ray andchemical. 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.

Disinfection is the killing of many, but not all microorganisms. Disinfectants are generally chemicals used on inanimate objects.

Antiseptics are disinfectants used on body surfaces.

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.

Dessication: Vegetative cells exposed to normal room air graually become dehydrated or desiccated. Delicate pathogens such as Streptococcus pneumoniae, the spiochete of syphilis or Neiseria gonorrhae can die after a few hours of air drying, but mahy others are not killed and some are even preserved. Endospores of Bacillus and Clostridium are viable for thousands of years under extremely drug conditions. Staphylococci and streptococci in dred secretions and the tubercle bacillus srrounded by sputum can remain viable in air and dust for lenghty periods. Many viruses (expecially nonenveloped) and fungal spores can also withstand long periods of desiccation. Desiccation can actually be a way to preserve foods because it reatly reduces the amount of water avilable to support microbial growth.

Lyophilization: is the combination of freezing and drying. It is a common method of presrving microorganisms and other cells in a viable state for many eyars. Pure cultures are frozen instantenously and exposed to a vacuum that rapidly removes the water. This method avoids the formation of ice-cyrsatls that would damage the cells.

Products for Disinfection

Detergents: target the cytoplasmic membrane of bacteria. These agents physically bind to lip layer of the cytoplasmic membrane which opens up the cytoplasmi membrane and allows damaging chemicals to enter the cell and important ions to exit the cell.

Alcohols are protein denaturants. A concentraiton of 50% and higher dissolve membrane lipids, isrupt cell sulrface tensiona nd compromise membrane integrity. Teh rte of evaporation decreases effectivneness and inhalaiton of vapors can affect the nervous system.

–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). A concentraiton of 60-80% alchol is deemed most efective due to the fact that proteins require water in order for denaturation to cocur. A concentration of 70% ethyl alchol requires a10 minutes to kills Staphylococcus aureus, 2 min to kills E coli and 10 minutes to kill poliovius.

Detergents: are polar molecules that act as surfactants. Anionic detergents have limited microbial power but cationic detergents such as quaternary ammonium compounds (“quats”) are effective. The positively cahrged end of the molecule binds the negatively charged bacterial surface proteins and the long, uncharged hydrocarbon chains allows the detergent to disrupt the cytoplasmic mebrane. Detergents are effective against virsues, algae, fungi and gram positive bacterial. They are used to clearn restaurant equipement, surfaces and restrooms. Some quats were banned in consumer products in 2017.

Hydorgen Peroxide. A 3% hydrogen peroxide can kills SA in 12.5 seconds, gonorrheae in 0.3 sec and herpes in 12.6 seconds.

Halogens oxidize. 2 types are 1) iodine and 2) chlorine (5% solution of sodium hypochlorite) 4) surfactants are hydrophobic and hydrophilic groups that solubilize.

–Chlorine (Bleach): Chlorine can kill TB in 50 seconds, entamoeba cysts in 150 minutes and Hepatitis A virus in 10 minutes. In solution, these compounds combine with water and release hypcholorous acid (HOCl) which denatures enzymes and suspend metabolic reactions. Chlorine is used to disinfect drinking water, sweage and waste water. Hypochlorites are used in health care to treat wounds, disinfect bedding and instruments, sanitize food equipement and in restaurants, pool and spas. Chloramines are alternatives to pure chlorines in treating drinking water.

—-Chlorhexidine: is a complex organic base containing chlorine and two phenolic rings. It targets bacterial membranes where slective permeability is lost, bacterail cell walls, and proteins resulting in denaturation. Its effects on virsues and fungi are variable. It is often used in hand scrubs, prepping skin for surgery, as an obstetric antiseptic and as a mucous membrane irrigant.

–Iodine: can kill endospores slowly and all other microbes. A 2% iodine and 2.4% sodium iodine (aquoues iodine) is used as a topical antiseptice. A 5% iodine and 10% potassium iodine is used as a dissinfectant for plastica nd rubber instruments as well as cutting blades. Iodine can be extremely irritating to the skin and is toxic when absorbed. Many iodophos were banned in consumer productsin 2017.

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 hexachloropheneand chlorhexidine which alters membrane permeability.

ultraviolet (UV) radiation: ranges in wavelenght of about 100 to 400 nm. It is most lethal from 240-280 nm with a peak at 250 nm. Because UV radiation passes reapidly through air, slightly through liquids and only poorly through solids, the object to be disinfected must be directly exposed to it for full effect.

UV is a pwerful method for destroying fungal cells and spores, bacterial vegetative cells, protozoa and viruses. Bacterial spores are about 10 times more resistant to radiation than are vegetative cells but they can be killed by increasing the time of exposure.

Germicidal lamps cn cut down on the concentraiton of airborne microbes by up to 99%.