Effects of Antibiotics on Bacterial Count

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Bacterial Count as Diagnostic Tool

Laboratory diagnostics provide essential information for physicians, particularly when determining a plan of treatment. When bacteria are involved in a disease or illness, the actual count of the bacteria per cubic millimeter can help the physician decide what dosage of antibiotic to prescribe. A urinalysis, which demonstrates the amount of bacteria present, usually quantified by streaking an agar plate with a calibrated loop. This gives an accurate representation of the number of bacteria that are present. The effects of antibiotics on bacterial count will be a reduced count.

Other specimens, such as those collected on a swab, will be affected by prior treatment with antibiotics. Whle the colony count will still grow on agar, the amount of growth may be impaired, due to the presence of the drug.

Since antibiotics begin working within a few hours, identifying the actual number of bacteria may be difficult. It is preferred to collect specimens prior to treatment with antibiotics, in order to gain accurate information.

Types of Antibiotics

There are many different types of antibiotics. Broad spectrum antibiotics work on a variety of organisms. Narrow spectrum antibiotics work on only a few. Some antibiotics are bactericidal, meaning they kill the bacteria. Others are bacteriostatic and prevent the multiplication of bacteria. Regardless of the type of antibiotic used, once a treatment begins it is important to complete the entire prescribed dose. Failure to do so may allow a particular bacteria to develop a resistance to the antibiotic being used.

How Antibiotics Work

Bacteria have cell walls that give integrity to the microorganism. The strength of the cell wall helps maintain structure under increased pressure, so the bacterial cell does not burst. The cell wall is made up of peptidoglycan, which forms a mesh-like structure. Some antibiotics, such as penicillin, inhibit the structure of peptidoglycan mesh and cause the bacteria to break apart. Other antibiotics, such as vancomycin, bind with the cell wall and prevent cross linking.

The type of antibiotic chosen for treatment comes from a sensitivity test. The sensitivity test determines the inhibitory factor of a variety of antibiotics against the bacteria that has grown. The test involves placing small disks with a concentration of antibiotic on an agar plate that is growing the bacteria. In areas where the bacterial growth has been inhibited, the antibiotic is effective and is likely to work against the infection. The effects of antibiotics on bacterial count are altered when a patient has already been treated with an antibiotic.

Caution Concerning the Use of Antibiotics

Many times, after beginning a treatment with antibiotics, people begin to feel better and discontinue taking the pills. It is important to complete the treatment, even if pain and symptoms have subsided. Bacteria can easily mutate, and discontinuing antibiotic treatment without completing the full dosage makes it possible for bacteria to become resistant to antibiotics. This is becoming more and more of a problem, and many physicians are choosing to avoid treating with antibiotics, if at all possible, to avoid the growing resistance to antibiotics.