November 14th - WAITING CULTURE AND SENSATIVITY TESTS

My Wednesday started early, 1:30 a.m. to be exact. The report that we received on Tuesday from A&M worked a number on me.  

As I had mentioned, the sample was sent via overnight on Monday for Tuesday a.m. delivery.  Hopefully they plated the the sample and started the bacteria culture and sensitivity tests. 

What is the culture? 
A urine sample is kept under conditions that allow bacteria and other organisms to grow. If few organisms grow, the test is negative. If organisms grow in numbers large enough to indicate an infection, the culture is positive. The type of organisms causing the infection are identified with a microscope or by chemical tests. 

Sensitivity, what is this? 
The bacteria are allowed to incubate for a day or two, and then the plate is examined to see whether the bacterial growth is inhibited (or not) by the antibiotics on each disk.

• SENSITIVE: In this case, a clear, circular "halo" (technically known as a "plaque," or zone of inhibition) will appear around the antibiotic disk, indicating an absence of bacteria. The antibiotic has inhibited their growth and/or killed them, meaning that this particular antibiotic should be effective against the infectionn.
• INTERMEDIATE: A somewhat cloudy plaque indicates that not all the bacteria in the area around the disk have been killed. This means that there are some members of the bacterial population that are sensitive to this particular antibiotic, but others that are genetically immune to its effects. If an antibiotic to which the bacteria show "intermediate" sensitivity is used, it is likely that the sensitive members of the bacterial population will be killed, and the resistant ones will survive, resulting in the selection of a population resistant to that particular antibiotic.
• RESISTANT: In this case, the filter paper will have no discernible plaque around it, meaning that the bacteria are growing normally, even in the presence of the antibiotic. An antibiotic producing no plaque will most likely be ineffective against the bacteria. 

The Petri dish in the image above (shamelessly borrowed from the University of Wisconsin at Madison online Textbook of Bacteriology, which includes a more detailed explanation of the appearance of the halos used in bacterial identification), shows bacteria being strongly and moderately inhibited by most of the antibiotics (impregnated on circles of filter paper), but unaffected by the antibiotics on the disks located at 5 o'clock and 9 o'clock on the dish. 

In three to seven days after the sample is taken, the vet will receive the results from the lab, including the species of bacteria and the range of antibiotics to which the bacteria are sensitive (S), resistant (R) and intermediate (I). Again, "sensitive" means that the bacteria were inhibited or killed by that particular antibiotic, and this is what you want to hear. 

Continuance on Darby:  I saw Darby getting more and more uncomfortable, and really debated on putting her on an antibiotic prior to the culture and sensitivity test being complete.  She has been on at least 3 this year and obviously none were effective.  Dr. Allen suggested Baytril.  Because I want the tests to be efficient and correct, I decided to put her on an antibiotic that could possibly help her feel better.  We may need to change it but at least she is one one now. I couldn't have her continue with this for more than 48 hours, keep in mind we had a pretty big sign last Thursday when we put her on the Piroxicam.  So from Thursday to Thursday would have been 7 days, and adding another 2-5 days is a big deal. 

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