This membrane of bacteria, they cannot protect themselves

This lesson will discuss how alcohol can be used as a disinfectant and antiseptic but not a sterilant.

We’ll also talk about what it kills and doesn’t kill and why ethyl alcohol and isopropyl alcohol are the two most commonly used alcohol-based disinfectants.

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The Pros and Cons of Alcohol

Alcohol: as one famous man once said, it’s the cause of, and solution to, all of life’s problems. That man was none other than Homer Simpson, of course. I can sit here and make an entire lesson out of quotes and jokes about alcohol. However, in this lesson, I’ll try to focus in on the effects alcohol has on microbes. Never mind the effects it has on you, such as headaches, loss of consciousness, severe liver damage and premature death.

Those aren’t all that important.

Types of Alcohol

The first important thing we need to talk about is the different types of alcohol available for use. Now, don’t get excited; this doesn’t mean we’ll be going on a trip to the liquor store any time soon.We’ll be talking about the types of alcohol that are used as a disinfectant or an antiseptic.

Those aren’t the same thing, by the way. Disinfection implies the death of most microbes on an inanimate object, while antisepsis implies the death of most microbes on living tissue, such as your skin.The difference is slight but still important. You can liken disinfection to a bacterium passing out on a floor, which is an inanimate object, while antisepsis implies that a bacterium passes out on a living friend after having too much from the tap after work.Anyways, these bacteria and other microbes can drink several different types of alcohol, including:

  • Ethyl alcohol: a type of alcohol commonly known as ethanol or grain alcohol
  • Isopropyl alcohol: an alcohol that is sometimes referred to as rubbing alcohol
  • Methyl alcohol: an alcohol that is also called methanol or wood alcohol

Mechanisms of Action

Methyl alcohol is very rarely used compared to rubbing alcohol or ethanol in medicine because it’s quite weak compared to the latter two when it comes down to disinfection and antisepsis. It’s like a light beer compared to whiskey or vodka.

Hence, we will just focus in on rubbing alcohol and ethanol as we move on in this lesson.The way by which these two alcohols destroy bacteria, viruses and fungi is through something known as protein denaturation. In basic terms, it’s a process whereupon a protein loses its higher-order structure. You can imagine that a protein is like a piece of metal.

That piece of metal can be formed into many different things. For example, it can be made into a paperclip. The shape of the paperclip is like that metal’s higher-order structure. If you were to physically unwrap and uncoil that paperclip into a straight piece of metal, you would have metaphorically denatured it.When you uncoil that paper clip, it is still a piece of metal, but it has lost its function.

It can no longer hold paper together. Likewise, when a protein is denatured by an alcohol, it’s still a protein, but it cannot perform the function it once could. Well, if the bacteria, viruses, and fungi cannot rely on their proteins to do their job, they simply die.Another way by which alcohol can kill is by damaging the outer membrane of bacterial cell membrane. It’s like damaging your skin. If you lost all of your skin, you would die, since you would be unable to protect yourself from the dangers of the environment around you.

Likewise, if you damage or dissolve the cell membrane of bacteria, they cannot protect themselves either and end up dying in the process.The good thing is that alcohol can kill many viruses, such as the influenza virus, which causes the flu, or the rhinovirus, which is responsible for the common cold. It can also kill plenty of dangerous bacteria, such as E. coli, and fungi, such as Cryptococcus neoformans. However, alcohol cannot destroy bacterial spores, which are very hardy forms of bacteria.Therefore, because alcohol cannot kill every microorganism on a surface, it is not considered to be a sterilant. Meaning, we shouldn’t be using alcohol on something like a surgical instrument, because a fatal infection during surgery may occur if a bacterial spore lodges into your body due to a dirty instrument.

Ideal Concentrations

Leaving that tidbit aside, we can focus in on one last important part of this lesson. I’m almost certain you know that people who aren’t nephalists, meaning people who don’t drink alcohol at all, have a preference for a type of spirit, wine, or beer; some like their drink really strong while others prefer theirs light and smooth.If we were to choose a preference for the type of alcohol we’d want to use to kill our microbes, we would definitely go with the strong stuff.That’s because alcohol, at concentration of between 60% and 90%, is most effective in its antimicrobial activity. Anything less than 50%, such as your typical alcoholic drink, is just too dilute to do the job well.

And if the alcohol is over 90%, it cannot enter the cell well enough to denature proteins inside of the microbe.

Lesson Summary

So, recall that the three main types of alcohol are known as:

  • Ethyl alcohol: a type of alcohol commonly known as ethanol or grain alcohol
  • Isopropyl alcohol: an alcohol that is sometimes referred to as rubbing alcohol
  • Methyl alcohol: an alcohol that is also called methanol or wood alcohol

Methyl alcohol is considered to be too weak to be used as a disinfectant. Hence, we stick to using the former two instead.

The way that these two alcohols destroy bacteria, viruses and fungi is through something known as protein denaturation. In basic terms, it’s a process whereupon a protein loses its higher-order structure.And don’t forget that the ideal concentration of alcohol for microbicidal activity is 60-90%.

Learning Outcomes

After finishing the lesson, you should recognize that the three main types of cleansing alcohols (ethyl, isopropyl and methyl) can be used as disinfectants or antiseptics.

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