How Do Drugs Work - Antibiotics - Part 1- Bacteria

Hello Everyone,

Before we talk about antibiotics, we need to know a little about the clinical bacteria that cause illness.

There are bacteria which normally occur on the outside of the body on our skin and in our nose and mouths. There are also bacteria that normally live inside our intestinal tract. Usually, those bacteria do not cause any problems for us. There are portions of the body that are sterile and do not contain any bacteria such as blood or spinal fluid.

So, a common organism that lives on the skin and is always present can cause significant problems if it gains entrance to an area that is usually sterile.

Knowing the type of bacteria that is causing an infection is usually one of the first things a physician needs to know. You are probably saying, "The last time I had an infection, the doctor prescribed an antibiotic right away. There in no way she could know what type of bacteria it was." True....kind of. There are many types of infection that are caused by the same types of bacteria. For example, pneumonia is usually caused by one of three types of bacteria. In addition, if the pneumonia was aquired out in the community or inside a healthcare facility will also give a clue as to the type of bacteria that cause the infection. Based on that knowledge, the physician can narrow the bacterial field and prescribe an antibiotic based on the suspected bacteria. Prescribing or administering an antibiotic based on common pathogens is called "EMPIRIC THERAPY".

However, knowing the type of bacteria is key. So, how are those bacteria classified?

Clinical bacteria are grouped into five categories based on gram stain appearance under the light microscope. Two groups have a general rounded shape (The COCCI) and stain either red or blue. Two groups have a general rod-like shape (The BACILLI) and stain either red or blue.

The organisms that stain blue or that can uptake the stain are called GRAM POSITIVE.

The organisms that stain red are called GRAM NEGATIVE.

There are some antibiotics that are affective against both Gram positive and Gram Negative organisms. Those are called BROAD SPECTRUM ANTIBIOTICS.

There are some that are effective against primarily Gram positive organisms as well as some that are effective against primarily gram negative bacteria.

Therefore, knowing if an organism is gram positive or gram negative is considered by many to be the single most important chacteristic of clinical bacteria.

Gram negative organisms have thinner cell walls and the cell wall composition is different from that of gram positive organisms. This difference also accounts for some general distinctions in susceptibility to antibiotic drugs.

In addition to the Gram Stain characteristic, knowing if the bacteria do or do not require oxygen to replicate is important. Some bacteria can grow only in the absence of oxygen and they are known as ANAEROBES. If they require oxygen, they are know as AEROBES. If the are flexible and grow in both conditions they are called FACULTATIVE ANAEROBES. Anaerobes account for 5 - 10% of all clinical infections. There are antibiotics that are effective against anaerobes.

Well, this is just a start and I will continue with my next post.

To be continued....

Dr. Paul