I am testing antimicrobial activity of oxacillin resistant staphylococcus aureus. I am looking for literature on the most recent protocol of MIC for ORSA / MRSA?
If you would like to consider an advanced method for determining MICs (and in general obtaining a better, dynamic understanding of the way antibiotics affect bacteria) see the Wikipedia article links below. The first is to the main article on isothermal microcalorimetry. The second is to a specific section of the article, in which you will find a discussion of this specific use, with citations to its use in detecting SA and MRSA and evaluating the effects of antibiotics on them.
https://en.wikipedia.org/wiki/Isothermal_microcalorimetry
https://en.wikipedia.org/wiki/Isothermal_microcalorimetry#Pharmacodynamics
It might also be important to consult the CLSI (http://www.clsi.org/) standards and guidelines.
In CLSI you can to obtain all the information about this (techniques, literature, normal values, etc.).
Thank you Carla Carneiro ma'am and José Antonio Álvarez Canales Sir....
I would like to know, is it necessary to use cefoxitin antibiotics to differentiate MRSA?
I usually use two antibiotics to screen for MRSA: cefoxitin and oxacillin. After that I always make a PCR to search for the mecA gene.
If SA is resistant, it will grow in the presence of a normally effective amount of either cefoxitin or oxacillin. While a genetic identification may be helpful, the basic definition of resistance in not whether a certain gene is present but whether there is growth in the presence of an amount of antibiotic that should eliminate growth. In our published study (attached), growth was slower in the presence of 4 mg/l of oxacillin than it was in the presence of 6 mg/l of cefoxitin. See Fig. 1B in the attached paper. Also, our iMC method illustrated that cefoxitin is bactericidal (causing a kill-back) rather than bacteriostatic (slowing the growth rate). As shown in Fig. 3B, increased amounts of cefoxitin delay detectable growth, but after it is detectable, the rate (slope of the accumulated heat vs. time data) is the same.
Cefoxitin is better than oxacillin because has a less false negative rate in results, using disk diffusion or micro dilution in broth.
Yes. Last time i had just used oxacillin and found 14 ORSA /MRSA but after following CLSI guideline i used both cefoxitin and oxacillin and found only 6 MRSA. I am wondering do i have to use both antibiotics for MIC. As I am not doing PCR for the gene detection. So, I want to know is it good to use only antibiotics to know MRSA or ORSA?
Is good, if you must to obtain a clinical result to reporting to physician. If you need to know is this information for researching, is convenient to complete data with PCR.
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