What is the formula for germicide that is sufficient to kill blood-borne pathogens?

A.1 ounce

B.2 ounce

C.3 ounce

D.4 ounce

Photo of Betadine, a povidone iodine antiseptic
Photo of Betadine, a povidone-iodine antiseptic

The correct answer is A. 1 ounce

Blood-borne pathogens are those micro-organisms that are contracted by a person making contact with contaminated blood. Various viral and bacterial infections can be transmitted in this manner. For example, viruses such as HIV, hepatitis B, Ebola, and Marburg are transmitted via blood and body fluids.

Certain microbial species can cause food spoilage and human disease. It is therefore important that ways are found to eliminate these harmful microbes from surfaces and foods before they reach levels that are harmful.

A germicide is any substance that can destroy microbes and usually, only a small quantity of about 1 ounce is needed to kill blood-borne pathogens. People have developed many chemical agents that have germicidal properties. There are different types of germicides that operate at different levels.

Antiseptics are germicidal substances that can be used on living tissues. These substances may be bacteriostatic, stopping the microbes from growing further, or they may be bactericidal (killing the bacteria).

Antibiotics are substances that are taken internally to kill bacterial infections. The main problem with these substances is the development of resistance by the bacteria. Antibiotic resistance is now a major problem leading to the death of many people each year.


These substances can be classified into different levels. Low-level disinfectants kill most of the vegetative cells of bacteria but not those of Mycobacterium tuberculosis, which causes tuberculosis. These disinfectants are used in hospitals and other healthcare settings as sanitizers.

Intermediate-level disinfectants are more powerful and do actually kill M. tuberculosis. In addition, they do also destroy fungi and have the ability to disable viral particles. The EPA classifies these agents as tuberculocidal hospital disinfectants.

An example of a substance that acts at an intermediate-level is alcohol, which is a bactericide. It does not kill spores, but it does kill the tuberculosis agent.

The most effective concentrations of alcohol to use are from 60% to 90% in water. They do kill fungi and viruses in addition to killing bacteria. Alcohol destroys the enzymes of bacteria such as Escherichia coli, by denaturing them.

The high-level disinfectants are able to kill bacteria, including at the spore level. These substances are thus capable of sterilizing areas. Steam is an effective method of sterilizing equipment and has the advantage of being non-toxic.

It is done by placing equipment inside a machine known as an autoclave. However, this can cause corrosion of substances in some cases.

Ethylene oxide gas is an alternative to autoclaving, but it is potentially dangerous to use since this gas can irritate the eyes and lungs. This is why the autoclave is often the preferred method when possible.


Antiseptics, unlike disinfectants, can be used on living tissues to kill bacteria. Thus, these are substances that are used to help reduce the chances of infection and sepsis of wounds.

Povidone-iodine is a commonly used antiseptic which kills bacteria by denaturing the proteins on the bacterial cell membrane.

This agent is very effective against a wide range of potential pathogens and thus is a very commonly used substance in healthcare. In fact, this is a commonly used surgical scrub that also works well and is not usually irritating to the skin.


These are substances which are taken internally and are aimed at killing harmful bacteria inside the human body. There are many categories of antibiotics but the increasing development of antibiotic resistance is posing a challenge for medicine.

Many species of bacteria can cause sepsis in people; and in infants, Streptococcus pneumonia and certain species of Neisseria are particularly dangerous. Infections are often acquired in the hospital, which is also where many problems of bacterial resistance are usually first detected.

Bacteria found on the skin can enter into open wounds, causing infection. If these bacterial species enter the bloodstream it can cause a person to become dangerously ill.

The bacteria Staphylococcus aureus and Staphylococcus epidermidis commonly infect blood from wounds and can get into plasma when blood is collected.


Multi-drug resistant bacteria now accounts for many deaths from infection around the world. Hospital-acquired infections are particularly troublesome since many patients are already immune compromised and thus very susceptible to infection. Such patients can rapidly deteriorate if bacterial infections cannot be brought under control.

Methicillin-resistant S. aureus has been very problematic, particularly in hospital settings. This species of bacteria was already resistant to penicillin by 1940 and is certainly a species that rapidly evolves to resist antibiotics.

The concern is that even if new antibiotics are found and developed, that bacteria will simply develop resistance to them. What has been noticed is that resistance happens more quickly with antibiotics that only target one specific trait or feature of a bacterium.

It is more difficult for bacteria to develop resistance when an antibiotic works on more than one target area of the cell.

Antifungals and antiparasitics

Antifungals are germicides that kill fungal cells by one of four mechanisms. Fungicides can stop DNA synthesis or the manufacture of sterols in the cell membrane. They can also target cell membranes and cell walls of the fungus.

It is rare for people to have severe internal fungal infections unless they have a very weak immune system. People more commonly get fungus on the skin, which is fairly easy to treat with topical fungicidal creams.

In some parts of the world blood parasites are a major problem. Malaria and trypanosomiasis are both illnesses caused by a protozoan parasite that is transmitted to people by an insect.

These parasites are very difficult to eliminate and people may remain chronically ill even when treated with an antiparasitic medicine.


Viruses cannot be killed with antibiotics which is why it is often harder to get rid of a viral infection. These can be some of the deadliest blood-borne illnesses; for instance, viral hemorrhagic fevers such as Ebola and Marburg both kill many people.

The HIV virus is another illness which is difficult to treat since it changes its form often. This means that drugs are not effective for very long.

There are vaccines for other blood-borne viruses such as yellow fever and hepatitis B. In fact, people often get vaccinated if they are traveling to a country where these illnesses are prevalent.


  1. DJ Weber, WA Rutala (2006). Use of Germicides in the Home and the Healthcare Setting Is There a Relationship Between Germicide Use and Antibiotic Resistance? Infection Control & Hospital Epidemiology.
  2. Centers for Disease Control and Prevention (2016). Guideline for Disinfection and Sterilization in Healthcare Facilities. Retrieved from cdc.gov.
  3. ARM Coates, G Halls, Y Hu (2011). Novel classes of antibiotics or more of the same?British journal of pharmacology.
  4. G McDonnell, AD Russell (1999). Antiseptics and disinfectants: activity, action, and resistance. Clinical microbiology reviews.
  5. Editors of Encyclopedia Britannica (2018). Antimicrobial agent. Retrieved from Encyclopedia Britannica.


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