Staphylococcus (Staph) is a common genus of bacteria, with Staphylococcus aureus causing most human infections. These bacteria frequently colonize the skin and nasal passages without causing harm, but they become a concern when they enter the body through cuts or abrasions. Staph is a leading cause of various skin infections, such as boils and impetigo, and can lead to more severe, systemic illnesses if the bacteria spread into the bloodstream. Alcohol is an effective germicide against Staphylococcus, but its success relies entirely on specific conditions, especially the concentration used.
Alcohol Concentration and Types Required to Kill Staph
Alcohol’s effectiveness as a disinfectant is highly dependent on its concentration, which must fall within a specific range to eliminate Staph. Solutions of alcohol between 60% and 90% are generally recognized as rapidly antimicrobial against bacteria like Staphylococcus aureus. Water in the solution is an important factor in the alcohol’s ability to kill the microbe.
The two main types of alcohol used for disinfection are Isopropyl alcohol (rubbing alcohol) and Ethanol, also called ethyl alcohol, which is the base for many hand sanitizers. While 70% concentration is a long-standing standard recommended for general disinfection, some research suggests that concentrations closer to 80% to 85% might offer enhanced efficacy against Staph species. Water acts as a catalyst, slowing evaporation and allowing the alcohol to fully penetrate the bacterial cell wall.
Conversely, higher concentrations, such as 99% alcohol, are actually less effective disinfectants than 70% solutions. When highly concentrated alcohol is applied, it immediately coagulates the proteins on the outer surface of the bacterial cell. This rapid coagulation creates a protective layer that prevents the alcohol from penetrating the deeper, interior parts of the cell, allowing the Staph bacteria to survive. The water content in a 70% solution ensures a slower, more complete denaturation process, leading to the destruction of the entire organism.
How Alcohol Destroys Bacteria
Alcohol kills Staphylococcus through a dual mechanism: physical disruption of the cell’s structure and chemical alteration of its internal components. The primary mode of action is the denaturation of proteins, the essential machinery of the bacterial cell. When the alcohol molecules penetrate the outer layers of the microbe, they cause these proteins to unfold and lose their functional shape.
This process disrupts the cellular functions necessary for the Staph organism to survive and replicate. The alcohol also acts as a solvent that dissolves the bacteria’s lipid membrane. This membrane’s disruption causes the structural integrity of the cell to fail.
The combination of denaturing internal proteins and dissolving the lipid membrane leads to a catastrophic rupture of the cell, known as lysis. This dual attack ensures the swift death of the Staphylococcus organism. This mechanism applies to vegetative bacteria (actively growing and reproducing), making alcohol a potent and rapid-acting germicide against Staph on surfaces and intact skin.
When to Use Alcohol and When to Use Alternatives
Alcohol is an effective choice for specific scenarios involving Staph, particularly hand hygiene and skin preparation. Alcohol-based hand sanitizers, which contain ethanol or isopropanol within the effective concentration range, are convenient and rapidly reduce Staph organisms on the hands when soap and water are not available. It is also the preferred agent for preparing the skin before a medical procedure, such as drawing blood or giving an injection.
Despite its germicidal strength against Staph, alcohol has limitations that make it unsuitable for all disinfection tasks. Alcohol is classified as a low-level disinfectant, meaning it is ineffective against bacterial spores, such as those produced by Clostridium difficile. Where spores are a concern, stronger alternatives like sodium hypochlorite (bleach) solutions or hydrogen peroxide are necessary.
Using alcohol on open wounds or deep cuts is generally discouraged by medical professionals. The alcohol not only causes immediate pain but can also damage the new, fragile tissue forming to heal the wound, which can delay the overall recovery process. Minor cuts and scrapes are best cleaned with mild soap and clean running water, which physically washes the bacteria away. For more significant wounds, sterile saline solution is the recommended cleansing agent because it is gentle on sensitive tissue while aiding in contaminant removal.