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April 4, 2019 – Chances are if you have a dog, at some point in their life they’ve been on antibiotics (this applies to people, too!). But what are antibiotics and how do they work? Let’s talk antibiotic science and what we’re seeing in our Golden Retriever Lifetime Study hero dogs.

While cancer is a major focus of the Golden Retriever Lifetime Study, we’re also interested in learning about other diseases affecting golden retrievers. Since the average age of our heroes is only 6, cancer has been a rare diagnosis so far (thankfully).

One problem we have noted, even in our youngest dogs, is a variety of infectious diseases, including bacterial infections. For example, 25% of the Golden Retriever Lifetime Study cohort have had at least one skin infection requiring treatment. Other commonly recorded infections include ear infections and urinary tract infections, with some dogs logging multiple infections each year.

Since 1928, when Dr. Alexander Fleming first observed a bit of mold growing on a petri dish was capable of inhibiting bacterial growth, antibiotics have become a powerful and life-saving tool to treat infections.

Antibiotics work in one of two ways: they either directly kill bacteria (bactericidal) or they inhibit bacterial growth (bacteriostatic), making it easier for the body’s immune system to kill the organism. Antibiotic choice depends on the location of the infection and the offending bacteria. It’s important to remember all antibiotics work in tandem with the immune system to destroy and eliminate invading organisms. Another important feature of antibiotics is they target features unique to bacteria, minimizing any collateral damage to the patient.

Antibiotics can attack many different parts of a bacterium. Antibiotics that interfere with the cell wall, or outer surface, of bacteria include the well-known penicillin family. Cell wall damage leads to the death of the bacteria. Other familiar antibiotics in this category include the cephalosporins and vancomycin.

Another prime target for antibiotics is bacterial DNA. Since DNA is the blueprint for all cell functions, antibiotics that interfere with these molecules tend to be bactericidal. Antibiotics in this category include metronidazole and fluoroquinolones such as enrofloxacin and ciprofloxacin.

Some antibiotics target the other important genetic material found in cells: RNA. You might remember from high school biology that RNA performs a number of functions in the cell, including acting as the template for protein synthesis. Proteins are required for almost all functions of cells, including bacteria. Commonly used antibiotics that inhibit RNA include the bactericidal drugs gentamycin and amikacin.

Other antibiotics target RNA but fall into the category of bacteriostatic drugs. These include several older but well-known antibiotics such as tetracycline and chloramphenicol.

Some antibiotics don’t fit neatly into any of the above categories. For example, the sulfonamides, the first antibiotics to be used in animals and people, work by inhibiting folic acid. Many of us recognize folic acid as an important B vitamin and it’s also needed by bacteria for protein and DNA/RNA synthesis. Sulfonamide antibiotics alone tend to be bacteriostatic. However, when combined with other folic acid inhibitors they become bactericidal. Trimethoprim-sulfonamide is a common example of this type of antibiotic.

Although antibiotic is the term we use most frequently when we think of treating infections, antimicrobial is a broader term encompassing not only antibiotics but also disinfectants, preservatives and antiseptics. Antimicrobials include topical agents such as bacitracin, polymyxin and silver sulfadiazine. Disinfectants and antiseptics also have antimicrobial actions.

Next month, we’ll explore another side of antibiotics – why they fail and how antibiotic resistance develops. The emergence of antibiotic resistance is a crucial public health threat and the best weapon we have is education.