UA C&S question

[djquiggles]

I was just hoping some more experienced nurses could help me out. I got a patients results of a UA C&S and I was not 100% sure on how to interpret them. I understand the R, S and I aspect but am not clear on the numeric values associated with the antibiotics and to choose the most effective. The MD was notified and ordered macrobid but I am not clear with reading the sensitivity report.

Here are some of the choices from the report, I have included some of the higher values and lower values to aid in understanding. (the patient has no renal insufficiency or allergies)

E. Coli colony count >100,000

Susceptibility

Cipro

Macrobid 32

Levaquin

Bactrim

I am looking to find the reasons why the higher numeric value was chosen. I am apparently wrong....but was under the impression that the lower the numeric value the more effective a antibiotic was and the higher the value meant more of the antibiotic was required?

Help if you can please!

[tokebi]

The numbers indicate the size of "zone of inhibition." Culture is grown on a plate with little disks saturated with each antibiotic. If the microorganism is susceptible to a particular antibiotic, it would not grow around that disk. More susceptible the organism to the antibiotic, the greater the zone of inhibition would be. See the picture:

[klone, MSN, RN]

So the greater the susceptibility to the antibiotic, the larger the zone, and the greater the number will be? Very cool. Thank you for the microbiology lesson! :)

[NRSKarenRN, BSN, RN]

The numbers indicate the size of "zone of inhibition." Culture is grown on a plate with little disks saturated with each antibiotic. If the microorganism is susceptible to a particular antibiotic, it would not grow around that disk. More susceptible the organism to the antibiotic, the greater the zone of inhibition would be. See the picture:

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Thanks for the explanation. I learn something new every day @ Allnurses.

[tokebi]

I'm glad I got to contribute to the learning opportunities of Allnurses. But the credit entirely goes to my amazing micro teacher from years ago. Thank you all the teachers out there!

[Aretaeus]

The smaller the number the better, i.e. they less of that antibiotic you need to inhibit the bacteria. Ideally you want to chose the lowest possible number. In vivo anything above a 2 you should essentially consider it a resistant organism to that antiobiotic. These results are usually reported as the - minimal inhibitory concentration -> (MIC), almost exclusively so in the US, which is the lowest concentration of drug that inhibits the growth of the bug. The MIC is usually expressed in µg/mL and sometimes there is a qualitative interpretation, as in: susceptible (S), intermediate (I), resistant ® like you mentioned.

tokebi's information though true does not answer the original question, tokebi is right that in the old days and in some parts of the world you will still find susceptibility reported in "zone size", usually in mm, but the results in the example are in MIC, you can tell because no one measures a zone size of 0.12 mm. The MD in question actually chose the worst possible option. Sorry for the 3 year old bump but I was searching for "UA" and didn't find many threads on it but this one, after reading it I thought thread needed a little healing.

Susceptible Susceptible

Intermediate Intermediate

Resistant Resistant

[klone, MSN, RN]

Aretaeus, I don't think you're correct in your interpretation of the report in the OP. I will get back to that when I have more time. (two years later, and I now have WAY more understanding and knowledge of C&S reports and UTI tx than I did when I previously posted in this thread)