In statistics there is a bell shaped curve.  Split the bell vertically and one has the high point considered 100.  From that point, going either direction, the levels reduce in equal proportion to the distance from the center.  Here is a graphic representation of the concept.  The greatest proportion of the population exists in the center of the graph with the outliers, the exceptions, being at the ends.  Consider this and apply bacteria to the picture.  The weakest bacteria occupy the lowest portion of the bell curve, most of the bacteria occupy the center and the most hardy, resistance bacteria occupy the top end of the curve.  Let’s say someone comes in with a urinary infection.  The doctor can approach this in a few manners.  One could be to provide a general coverage antibiotic and hope that the bacteria present would be susceptible, another would be to provide a general cover antibiotic and at the same time do a urine culture, then change the antibiotic later according to the culture’s results.  The last method would be to do the culture and only provide antibiotic upon the results.  I could describe the means the culture provides the information, but will save that for some post in the future.  At 48 hours past incubating the bacteria, the lab checks the results and sends the doctor a report listing the antibiotics for which the bacteria is susceptible as well as the bacteria which are thumbing their nose at the treatment.  The doctor then looks at the allergy and other clinical information of the patient and prescribes the antibiotic.  Know that this is the reason there is not an instant answer to what bug is there when the lab is done.

Back to the bell curve for a moment.  When the antibiotic is taken, the bacteria in the lower portion of the bell curve are quickly removed as they are the weak ones.  It takes a little time to move up the bell curve and kill the bacteria occupying most of the bell curve’s area.  At this point, the patient is feeling much better and may start to behave like my grandmother.  There was an upper cupboard which was covered on the bottom shelf with partial bottles of various antibiotics under the idea that “if I feel that coming on again, I can take it.”  Sound familiar?  Remember that the upper portion of the bell curve is still there.  This is the section representing the most antibiotic, hardiest bacteria.  If these are not removed, guess the characteristic of the subsequent bacterial infection.  Yes, the bulk of the bacteria now are of the hardier variety.  The bell curve still applies meaning of the hardier variety, there are still some more resistant and strong than their parents.  Keep cycling this concept and you come up with antibiotic resistant bacteria.  It’s no more complicated than that.  (Now I’m wearing my nurse hat)  When instructed to take all of the antibiotic regardless of feeling better, this is the reason.  We, in the medical community, want to ensure the most resistant bacteria of any given infection are killed so they may not have stronger babies – because any remaining bacteria will be of the stronger variety.  That will also save us nurses from having phone calls like:

Mrs UTI: I have an infection and was wondering if it would be all right to take the Cipro I have left here.  It’s still in date.

Me: How do you know there’s an infection?

Mrs. UTI: my urine is cloudy.

Me: Well, you need to have that tested so that the antibiotic given may match the bug there so the infection is actually treated.  Remember that if the bug is not susceptible to the antibiotic, it can stick out its tongue at the treatment and keep on going.

Mrs. UTI:  OK.  I will go in.

It’s for your health as well as the population’s general health that we say to take all of the treatment.  Thank you.  Class dismissed.