Concentration of disinfectant vs growth of bacteria

[petra_riddell]

Hi,

At school we are doing a fair test and i'm just wondering why higher concentrations of disinfectant means no bacteria or less bacteria grows around the filter paper with the disinfectant in it? What makes disinfectant kill bacteria?

Thanks,
Petra

[SciB]

Hi Petra. That's actually a very good question because killing bacteria, especially the bad ones that cause human disease, is really important. The term 'disinfectant' refers to anything that kills, disables or removes an infectious agent, usually from the surface of inanimate objects. That means there are a lot of different kinds of disinfectant and they don't all work the same way.

Clorox bleach is one of the commonest and best disinfectants because it can kill almost anything. Chemically it is a solution of sodium hypochlorite, a compound that can release chlorine, a highly toxic oxidizer. When chlorine comes in contact with the proteins and lipids in the bacterium it reacts with them and makes them inactive. Without its proteins the bacterium dies.

Hydrogen peroxide is another oxidizer that kills bacteria, viruses and some fungi.

Rubbing alcohol, chemically known as isopropanol, is commonly used to swab your skin before drawing blood or giving an injection to disinfect the area. Ethanol can also be used. Alcohols damage the proteins and lipids of the bacterial cell and kill it.

When i was a kid and got a scrape on my knee, my mom put iodine on it to prevent infections. it stung because the iodine was dissolved in alcohol. nowadays there are modified iodine formulations like povidone that work just as well and are not so toxic to your own cells.

These are some of the main types of disinfectant. You see that most of them work by reacting with the bacterial proteins, lipids or nucleic acids and disabling or killing the microbe. Disinfectants are used to remove bacteria from surfaces. You would not want to cleanse your body with Clorox because it is also harmful to your cells. Killing bacteria that are infecting your body requires a special type of chemical called an antibiotic that is specifically harmful to bacteria but not to your body's cells.

I hope this answers your question. If you have more questions there are many online sites that can teach you about bacteria and how to control and use them. Remember, the majority of bacteria are harmless to humans and in fact the human body has a whole population of good bacteria that can help prevent infection by the bad ones and provide useful nutrients within our digestive system. These bacteria form what is called the 'microbiome' in your body. If you google this term you will find a whole lot of amazing information about this currently hot area of research. Your microbiome can affect your health in many ways from reducing obesity to making you feel happier. Read about it--it's really fascinating!

Have a wonderful summer and keep asking those questions!

Sybee

[petra_riddell]

Thanks heaps! This answered my question really well! The stuff about 'microbiome' looks really interesting too, I'll defiantly look into it.