I'm currently doing PCR of TEM genes from environmental samples, and the results are that there aren't any TEM genes present. However, in the same sample, Aeromonas bacteria isolated by me on culture medium supplemented with antibiotics had antibiotic resistance genes.
No.
"All recent studies predict an ancient origin of resistance that long precedes the use of antibiotics in the clinic." - Perry J, Waglechner N, Wright G. The Prehistory of Antibiotic Resistance. Cold Spring Harb Perspect Med. 2016 Jun 1;6(6):a025197. doi: 10.1101/cshperspect.a025197
These genes are present already in the isolated bacteria in low frequency, below sensitivity of your PCR test, and growth on culture medium supplemented with antibiotics selected bacteria with resistance.
Hello,
We would first need to ensure that there is not a technical problem.
1) For the absence of gene amplification, did the PCR work? Are the primers good? Is there a positive control?
2) For growth in the presence of the antibiotic. Does the antibiotic work? sometimes storage conditions can affect it. Also, is the growth inhibitory concentration, by the antibiotic, reached in your culture medium.
Resistance genes are NOT going to arise de novo by plating cells on antibiotic plates. It is possible that you can get point mutations which confer resistance to some antibiotics, but for some other antibiotics there are not point mutations that will confer good resistance. However if there are other sources of the resistance genes in the sample (such as in environmental samples) there are many mechanisms but which they can be exchanged or transferred.
Michael J. Benedik Related question- Can antibiotic-resistant phenotype arise due to gene deletion/gene function loss? Is there any case? If so, such antibiotic can stimulate the mutation (purely in theory).
Watch this video and see evolution in action in real time. This is the best demonstration I've seen.
https://www.youtube.com/watch?v=yybsSqcB7mE&pp=ygUdYmFjdGVyaWFsIGV2b2x1dGlvbiByZWFsIHRpbWU%3D
Alex Ignatov I can not think of any example where a gene deletion would cause antibiotic resistance for normal antibiotics that are in use. By definition the target of an antibiotic would need to be an essential gene/component/pathway of the bacterium. So if you could delete that gene then by definition it would not be essential and not a good target for an antibiotic.
Theoretically you might have a situation where by deleting some transport function in the cell then the antibiotic can't enter the cell and so would not have any antimicrobial effect. But practically speaking that scenario would lead to a high rate of resistance to the antibiotic and so drug would be been rejected as not a suitable drug choice early in the process of its development.
Extending that discussion beyond antibiotics, you can find many scenarios where a gene deletion would confer resistance to bacteriophage infection or to bacteriocin action. These are well known and well studied. The "agent" (phage or bacteriocin) does provide a selection for the mutant but does not stimulate the mutation per se. There were seminal experiments done in the 1940s and 1950s that asked the question whether mutations arose at random but were found because of the selection or are the independent of the at random or were "programmed" by the selective agent. The finding was they arose at random. This is the classic Luria-Delbruck experiment of 1943 (phage resistance) and later the Lederberg and Lederberg experiment of 1952 (antibiotic resistance) which asked if an antibiotic resistance mutation arose because of the drug or was pre-existing in the population (they of course found the latter was true).
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