The nature of bel-1 attC stabilizes its genetic environment and contributes to antibiotic resistance spreading
The rapid emergence of antibiotic resistance is a worldwide crisis, endangering the efficacy of antibiotic treatment. Multidrug resistance in Gram negatives is now recognized as an issue of worldwide interest. Those bacteria possess various resistance mechanisms compromising the efficacy of several classes of antibiotics such as beta-lactams.
In this study, we investigated the blaBEL-1 gene which encodes an extended-spectrum β-lactamase, BEL-1, that is present at the second position of the variable region of class 1 integrons identified inPseudomonas aeruginosa. Class 1 integrons are genetic elements that can acquire and rearrange gene cassettes, including genes carrying antibiotic/disinfectant resistance genes, therefore participating in the evolution toward multidrug resistance. The bel-1 cassettes are associated with aacA4 and aadA5 gene cassettes, coding for an aminoglycoside-modifying enzyme, and also with the smr cassette, encoding resistance to antiseptics.
Fig. 1. Schematic representation of integrons containing theblaBEL-1 gene found in clinical strainP. aeruginosa51170. Arrows, orientation of gene transcription; black and gray circles,attCandattI1sites, respectively.
Integrons are bracketed by two segments at their 5’ and 3’ ends. The 5’ includes intI1, a gene encoding a site-specific recombinase of the DNA integrase family, with attI being the cassette integration site and the promoter Pc driving the expression of the cassettes. The gene cassettes are independent units each consisting of a gene bracketed by copies of a recombination site named attC. attC sites are involved in site-specific recombination catalyzed by the integrase IntI1 leading to cassette integration or excision.
We investigated here the putative mobility of the bel-1 gene cassette and the role of several antibiotic molecules in the putative induction of its mobility. Interestingly, we found after 10 days ofP. aeruginosaculture with sub-inhibitory concentrations of antibiotics, that the bel-1 cassette remained at the second position in the integron, highlighting its stability inP. aeruginosa.
Therefore, the effect of IntI1 integrase overproduction was investigated. The cointegration frequencies depend on the recombination efficiency of theattCsite available for recombination in the donor integron. We showed that thebel-1 attCsite was likely inefficient for recombination with theattI1site or anattCsite in a receiving integron In3. Thesmr2 attCsite was thus more efficient for recombination than thebel-1 attCsite itself.
The excision/mobilization experiments showed that theattCsite of thebel-1gene cassette was inefficient and that this gene cassette was not mobilizable independently. This might likely be explained by the sequence of thebel-1 attCsite itself, which does not correspond to the ones better recognized by the Int1 integrase. Here the extrahelical bases constituting thebel-1 attCbottom strand are distantly related to those well recognized by Int1. We also showed that thesmr2 attCsite is enhanced over thebel-1 attCsite, as it is involved in almost all recombination events when both gene cassettes are present on a plasmid.smr2always remained associated with thebel-1gene cassette.
Overall, our work provides some insights into the organization ofblaBEL-1-containing integrons. It is likely that those later evolved from a common ancestor carrying an early association between thebel-1andsmr2gene cassettes. It is also possible thatsmr2was responsible forbel-1gene cassette recruitment and for the comobilization ofbel-1–smr2into class 1 integrons. AlthoughblaBEL-1-containing integrons are subject to gene cassette rearrangements, we propose that the nature ofbel-1 attCstabilizes its genetic environment, probably by impairing recombination events that could lead to its loss and thus maintaining antibiotic resistance.
Nacim Bouheraoua1,Laurent Poirel2-5,Patrice Nordmann2-5
1Quinze-Vingts National Ophthalmology Hospital, Sorbonne Université, Paris, France
2Medical and Molecular Microbiology Unit, Department of Medicine, Faculty of Science, University of Fribourg, Fribourg, Switzerland
3INSERM European Unit (IAME, France), University of Fribourg, Fribourg, Switzerland
4瑞士国家新兴Antib参考中心iotic Resistance (NARA), University of Fribourg, Fribourg, Switzerland
5Institute for Microbiology, University of Lausanne and University Hospital Centre, Lausanne, Switzerland
Publication
Integrase-Mediated Recombination of the bel-1 Gene Cassette Encoding the Extended-Spectrum β-Lactamase BEL-1.
Bouheraoua N, Poirel L, Bourreau B, Bonnin R, Laroche L, Naas T, Nordmann P
Antimicrob Agents Chemother. 2018 Apr 26
Related Articles:
|
Carbapenem-resistant Enterobacteriaceae: fighting mutantsAntibiotic resistance occurs when bacteria causing an infection survive after being exposed to a drug that, under normal conditions, would kill it or inhibit its growth. As a result, this… |
|
Rapid monitoring of the impact of polymicrobial infections…The development of bacterial infections is a major challenge as pathogenic bacteria spread through healthcare facilities where patients may come in contact with complex bacterial communities heavily colonizing on hospital… |
|
New antimicrobial strategies against multidrug-resistant…Due to current antibiotic resistance worldwide, there is an urgent need to find new alternative antibacterial approaches capable of dealing with multidrug-resistant pathogens. In fact, the World Health Organization has… |
|
Antibiotic tolerance in bacteria: how to regain…Bacteria use a plethora of mechanisms to evade killing by antibiotics. Resistance is the best documented mechanism. Here, genetic changes in the bacterial DNA result in antibiotic insensitivity. As a… |
|
BioID screen for bacterial virulence proteins: new tools for…The discovery of penicillin in the 1920s revolutionized our ability to treat bacterial infection. However despite the introduction of antibiotics, infectious bacterial pathogens remain an immense challenge for the healthcare… |
|
Campylobacter antimicrobial resistance in dogs and humansCampylobacteriosis has been the most frequently reported zoonotic disease in humans in Europe since 2005, and the annual number of notified campylobacteriosis cases has increased in many European countries in… |
Leave a Reply
You must belogged into post a comment.