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Antibiotic Resistance Question - (Nov/29/2009 )

Hello all,

1) I examined an isolated colony of a bacterial species from my nose - and it turns out it is resistance to certain antibiotics while susceptible to others. Would I expect a second isolate from the same source (my nose) to share similarities in antibiotic sensitivity with my current isolate?

Attempt: i am thinking that the answer is no, since there are many different bacteria that are part of our normal flora on the skin - thus the second isolate may be of a different species which may have different resistance/susceptibility to different antibiotics. so i don't think location on the human body plays a factor in determining which organisms become resistant/susceptible - but i am not sure about this.

2) I ran a agarose gel electrophoresis of a plasmid of a Staph. captis species along with a control Staph. schleiferii species. I am asked: is it likely that any of the antibiotic resistances of Staph. captis and the control Staph. schleiferii would be encoded by genes located on a plasmid? How might you determine if this were truly the situation?

first step I think is involved is to see if Staph schleiferii and Staph. captis have any similar antibiotic resistances or susceptibilities. if they do, we check the agarose gel electrophoresis photo of the plasmids from the two different species, and check whether they have any same sized plasmids - if so, it might be possible that they possess the same plasmid - and if they also have resistance for the same antibiotics then this will further support that possibility .

i also thought we can do rapd pcr on one specific resistance gene and check if it is on the will show up on gel if not then nothing on gel saying i will be on the host chromosome genome

thank you!


1) There are many different species of bacteria up our nose but isolates with similar resistances are likely, especially if you have just been treated with the antibiotics. Having said that, many of these sorts of genes are contained on plasmids and can be transferred between bacteria only if they are compatible. If your second isolate was the same species or even genus, I would expect similar resistance, if another genus probably not.

Note that I am not a microbiologist and it is a number of years since I did this sort of thing... so take what I say with a grain of salt.

2)It is highly likely that antibiotic resistance is on a plasmid... most of them are! I would take the plasmids and a strain of antibiotic susceptible bacteria and transform the plasmids into the bacteria and plate on a number of different plates... I am sure you can figure the rest out (think about what you are testing for).

In terms of screening lots of plasmids for lots of genes, you could try plain PCR for the genes - some sort of genotyping reaction would do - amplify short specific sequences from each resistance gene with a negative result indicating that it isn't there. RAPDs wouldn't be much good for this, the primers are too short to be specific for any gene, you are likely to get different results with each plasmid, as most of them have quite different sequences.