Antimicrobials describe a broad group of drugs that are used to kill pathogens (germs that are foreign and potentially harmful to an individual) or impair their ability to reproduce. Within this category are several subgroups of antimicrobials.

Antibiotics are drugs that have a specific action against bacteria. These are the most commonly used antimicrobial agents. Antibiotics do not work against viruses and should not be used to treat viral infections. Penicillin was the first antibiotic ever developed.

Antifungal agents are drugs that specifically attack fungal or yeast infections.

Antiviral agents are drugs that work to interfere with the viruses ability to replicate itself (make copies of itself). The effectiveness of antivirals depend upon the type of virus. Antivirals are not effective for all viruses, and most infections due to a virus will resolve without treatment. An example of a virus is influenza. Although antibiotics are not effective against viral infections, patients may develop bacterial infections after being ill with a virus (e.g. they may develop pneumonia). This bacterial complication may be treated with antibiotics.

Antimicrobial Stewardship:  The CCTC participates with an antimicrobial stewarship team that that includes the Critical Care Consultant, an Infectious Disease physician (who specializes in antimicrobial therapy), an Infectious Diseases Pharmacist and a CCTC Pharmacist.  This team reviews the cultures of all patients in CCTC to identify the best treatment.  This program helps to reduce inappropriate antimicrobial usage and ensure the best agent is used when treatment is needed.


Antibiotics are not all equal. Antibiotics that are effective against one type of bacteria may not work against another. To select the best antibiotic, samples of infected drainage or fluid are collected from the patient and sent to the lab for "culture". A sample of the fluid is rubbed over a special culture plate (Image 1). This plate provides an environment that encourages the pathogen to grow. After a day or more, the culture is examined under a microscope to identify the shape and characteristics of any bacteria. This allows the physician to choose antibiotics that will work against a particular category of bacteria. The final report can take several days to complete. It will identify the specific type and number of bacteria present. The lab will not describe a culture as "negative" (no growth of pathogens) until the culture has been monitored for several days. This is why it can take several days for a culture report to come back.

Once the type of bacteria is identified, the lab technologist can report the type of antibiotics that work best against the specific bacteria. This is called a drug "sensitivity report". If the bacteria is sensitive to a specific antibiotic, the antibiotic will be effective in destroying the bacteria. If the bacteria is resistant to an antibiotic, it needs to be switched to a more effective agent. It usually takes at least 24 hours before we have a preliminary report. When a patient is critically ill from a suspected infection, antibiotics that work against the largest number of bacteria are started first.

Antibiotics that have the "broadest" action are called Broad Spectrum Antibiotics. Broad spectrum antibiotics are very valuable when we do not know the cause of the infection, especially when patients are very ill. Unfortunately, they may also be more toxic to some of the body's organs (e.g., the kidney) and are more expensive. They may also kill our "good bacteria", allowing other bacteria to take over. As soon as we know the actual cause of the infection, the antibiotics are "fine tuned" by changing the antibiotic to one that is more bacteria specific. We are careful to avoid over-use of antibiotics due to the risk that bacteria might become resistant to our antibiotics.

When patients are admitted with a serious infection, one of the hospital Infectious Disease Physicians will see the patient daily and participate in the treatment plan.

Image 1: Bacteria growing on a culture plate.




Last Updated: October 23, 2014



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Last Updated October 23, 2014 | © 2007, LHSC, London Ontario Canada