Different antibiotics on Gram positive and Gram negative bacteria

[garytse86]

Hi. I am doing an investigation on the effects of different antibiotics on Gram positive and Gram negative bacteria.

1) Can you say that antibiotics and bacteria form a chaotic system? Can a very small change in concentration of antiboitics, or a small variation in pH, change the diameter of killing zone greatly?

2) If I want to extend this investigation: not only testing effects of antibiotics on Gram positive and Gram negative bacteria, but also "mycoplasmas" which are neither Gram positive nor negative. Is this possible? (I do not actually have to carry this out but just need to propose what needs to be done). Before I used the Mann Whitney U Test to comparing two sets of data. But if I introduce mycoplasmas, which statistical tests are there to comparing three groups of data?

Thank you very much for your help in advance.

Gary

 

[iansmith]

1) Can you say that antibiotics and bacteria form a chaotic system? Can a very small change in concentration of antiboitics, or a small variation in pH, change the diameter of killing zone greatly?

It will depend on the antibiotics, the pH value of media and how much a small variation in pH is. for example, quinolone have a decrease activity below ph 5.0 and macrolides have a decrease acitivity just below pH 7.0. Also, the penetration by aminoglycosides inside the cell is greatly reduce at low pH.

For reference
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8404912&dopt=Abstract

2) If I want to extend this investigation: not only testing effects of antibiotics on Gram positive and Gram negative bacteria, but also "mycoplasmas" which are neither Gram positive nor negative. Is this possible? (I do not actually have to carry this out but just need to propose what needs to be done). Before I used the Mann Whitney U Test to comparing two sets of data. But if I introduce mycoplasmas, which statistical tests are there to comparing three groups of data?

first mycoplasma lack a certain feature that are present on both gram positive and negative. this will have an influence on the result depending on the mode of action of the antibiotics.

For the stat test, look at the following page to guide you
http://www.edu.rcsed.ac.uk/statisti...o help decide the statistical test to use.htm